Patent Grant
8351842
1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a filtering circuit, and more particularly to a filtering circuit which can suppress a jammer in a wireless communication system.
2. Description of the Related Art
In a multi-channel wireless communication environment, we have not only the signal in a desired channel, but also jammers in other channels. All of the jammers should be suppressed so strongly that the signal to noise ration (SNR) of the desired signal can be improved to a level necessary for successful wireless communication.
A channel selection filter with the frequency characteristic to pass only the signal in the desired channel is needed to suppress jammers. The bandwidth of the filter corresponds to that of the channel bandwidth.
A short-range communication system has a narrow channel bandwidth of less than 1 MHz, while some other communication systems have much wider channel bandwidths, for example, 20 MHz for Wi-Fi and more than 4 GHz for ultra-wideband (UWB).
Generally, in an integrated circuit (IC), the die area of an analog filter is inversely proportional to the frequency bandwidth. This means that the analog channel selection filter in a short-range communication system would typically occupy more than half of the entire wireless IC. A digital filter is used for channel selection in most of the commercial wireless IC's for a short-range communication system since a digital filter can be implemented with much smaller area than an analog filter.
In the case of using a digital filter for channel selection, analog signals including the desired signal and jammer signals must be converted to digital signals before suppressing jammers. Given that a wireless IC should provide successful communication under jammers 40 dB larger than the desired signal, an analog-to-digital converter (ADC) should have a 40 dB wider dynamic range than it should have without the presence of jammers. Therefore, the ADC is required to have higher resolution, leading to larger power consumption.
The block diagram shown in
This architecture has two signal paths between a mixer circuit and an ADC.
In the first path, the jammers are extracted from the input signal by suppressing a desired signal. The input signal to the first path is converted to a digital signal using an ADC with a low resolution. Subsequently, only the desired signal is suppressed using a digital band stop filter. Finally, the digital signal that contains only the jammers is converted back to an analog signal.
In the second path, the input signal is delayed such that that jammers in the output of the second path are synchronous with jammers in the output signal of the first path.
The output signal from the first path consists of only jammers while the output signal from the second path consists of the desired signal and jammers. The jammers can be suppressed by subtracting the output signal in the first path from the output signal from the second path.
Since this architecture shown in
However, the architecture shown in
The delay circuit in the second path consists of sample and hold circuits connected in series as shown in
The number of sample and hold circuits, Nc, is equal to the total delay time required for the delay circuit, Td, divided by the sampling time of the sample and hold circuit, Ts, as in the following equation 1:
Nc=Td/Ts Equation 1
Td is set to a value equal to the delay time seen by the jammers going through the first path. This delay is nearly equal to the reciprocal of the bandstopwidth of the digital band stop filter in the first path, which corresponds with the bandwidth of the desired channel.
Ts is typically set to one-quarter of the reciprocal of the entire bandwidth of all the signals including the desired signal and jammers.
This architecture usually needs more than 100 sample and hold circuits in a narrow band communication system.
Since a delay circuit introduces noise, such as thermal noise and switching noise, this architecture makes the SNR significantly worse.
Exemplary embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an exemplary embodiment of the present invention may not overcome any of the problems described above.
The present invention provides a filtering circuit occupying a small integrated circuit die area and having a high SNR.
An aspect of the present invention provides a filtering circuit.
The filtering circuit may include a jammer generator, which includes a detector to acquire information about the period and phase of a jammer signal in a composite input sine-wave signal, which includes the jammer signal and a desired signal, to the jammer generator, and a pseudo sine-wave generator to output a pseudo sine-wave signal whose period and phase correspond with those of the jammer signal acquired at the detector; and an adder which outputs a difference between an input and an output signal of the jammer generator as the desired signal.
Another aspect of the present invention provides a variable gain amplifier whose output signal is input to the jammer generator.
Yet another aspect of the present invention provides a gain controlling circuit which includes a circuit for acquiring information of the amplitude of the jammer signal in the composite input signal and adjusts the gain of the variable gain amplifier so that the amplitude of the jammer signal in the output of the variable gain amplifier corresponds with that of the output of the jammer generator.
The present invention generates a pseudo-sine wave signal whose frequency, phase, and amplitude are approximately equal to those of a jammer included in a wireless signal and then outputs a difference between the wireless signal and the pseudo sine wave signal to yield a desired signal. As a result of the above, jammer suppression in a wireless signal may be achieved without any analog delay circuit.
Still another aspect of the present invention provides a method of detecting a desired signal in the presence of jammer signals, the method, including acquiring information of period and phase of an input sine-wave signal with a detector, generating a pseudo sine-wave signal whose period and phase correspond with the period and phase of the input sine-wave signal of a pseudo sine-wave generator, adding the input sine-wave signal at a non-inverting terminal of an adder and the pseudo sine-wave signal at an inverting terminal of the adder, and outputting a difference between the input sine-wave signal and the pseudo sine-wave signal.
Aspects of the present invention can make it possible to realize a filtering circuit with a small die area and a little degradation of signal-to-noise ratio (SNR).
These and other aspects of the invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings in which:
Hereinafter, certain exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The matters defined in the description, such as a detailed construction and elements thereof, are provided to assist in a comprehensive understanding of the invention. Thus, it is apparent that the present invention may be carried out without those defined matters. Also, well-known functions or constructions are omitted to provide a clear and concise description of exemplary embodiments of the present invention.
First Exemplary Embodiment
The first exemplary embodiment of the filtering circuit 300 contains a variable-gain amplifier (VGA) 310, a jammer generator 320, an adder 330, and a VGA-controller 340.
The VGA 310 adjusts the amplitude of its output signal by varying its gain. The gain may be controlled via an external control signal. The VGA-controller 340 controls the VGA gain so that the amplitude of the VGA output signal may be set to a desired value. The jammer generator 320 identifies the frequency and phase of its input signal, i.e., the VGA output signal, and then outputs a sinusoidal signal with the same frequency and phase as its input signal and with preset amplitude. The adder 330 outputs a difference between signal voltages input at its positive (+) terminal and negative (−) terminals.
The input terminal of the first exemplary embodiment of the filtering circuit 300 is internally connected to the input terminals of the VGA 310 and the VGA-controller 340. The output terminal of the VGA 310 is connected to the input terminal of the jammer generator 320 and the positive (+) terminal of the adder 330. The output terminal of the VGA-controller 340 is connected to a control terminal of the VGA 310. The output terminal of the jammer generator 320 is connected to the negative (−) terminal of the adder 330. The output terminal of the first exemplary embodiment of the filtering circuit 300 is internally connected to the output terminal of the adder 330.
In a wireless communication environment, a plurality of channel signals (Smulti) may be input to this exemplary embodiment simultaneously. One channel signal in the plurality of channel signals Smulti is a desired signal (S1) and the other channel signals are all considered jammers. Here, it is assumed that the power of a specific jammer (J1) is higher by Pj1 dB than the summation of the power of any other channel signal including S1. It is also assumed that the modulation type of J1 is frequency-shift-keying (FSK) and its modulation index, frequency deviation, and carrier frequency are known as m, Fdiv (Hz), and Fc (Hz), respectively.
Smulti is processed by the VGA 310 for amplitude adjustment and then fed to the input terminal of the jammer generator 320 and the positive terminal of the adder 330. The jammer generator 320 identifies the information of the frequency and phase of J1 in Smulti and outputs a sinusoidal signal with the same frequency and phase as J1. This sinusoidal signal is input to the negative terminal of the adder 330. The VGA controller 340 identifies the magnitude of the amplitude of J1 in Smulti and controls the VGA gain so that the amplitude of the VGA output signal is approximately equal to that of the output signal from the jammer generator 320. Thus, the J1 signal at the positive terminal of the adder 330 almost agrees with the sinusoidal signal at the negative terminal of the adder 330 in amplitude, frequency and phase. Therefore, only J1 in Smulti is suppressed at the output terminal of the adder 330.
The configuration and operation of the respective circuit blocks are described as follows.
The VGA 310 may include a number, N, of VGA_cells 3101 and has a differential input terminal (in_vga), differential output terminal (out_vga), and N-bit control terminal (cont_vga). Each VGA_cell 3101 has a differential input terminal (in_cell), differential output terminal (out-cell), and a control terminal (cont_cell). The differential input terminal of the VGA 310, in-vga, is internally connected to the differential input terminals of all the VGA_cells 3101, in_cell. The differential output terminal of the VGA 310, out_vga is also internally connected to the differential output terminals of all the VGA_cells 3101, out_cell. The N-bit control signal input to the N-bit control terminal of the VGA 310, cont_vga, provides a logic signal to the control terminal of each VGA_cell, respectively.
The VGA_cell 3101 may include a differential amplifier (DIFF1) 3110, a switch circuit (SW_VGA) 3120, and a current mirror circuit (CM1) 3130. DIFF13110 may include three N-type MOSFETs (M_n1, M_n2, M_n3) and two P-type MOSFETs (M_p1, M_n2). The sizes of M_n1 and M_p1 are the same as the sizes of M_n2 and M_p2, respectively. The gate terminals of M_n1 and M_n2 are referred to as the differential input terminal of the VGA_cell 3101, in_cell_p and in_cell_n. The source terminals of M_n1 and M_n2 are connected to a drain terminal of M_n3 which serves as a current source. The source terminal of M_n3 is connected to a ground line. M_p1 and M_p2 serve as current sources. The source terminals of M_p1 and M_p2 are connected to the power line and the drain terminals of M_p1 and M_p2 are connected to the drain terminals of M_n1 and M_n2, respectively. CM13130 may include an N-type MOSFET (M_n4) and a P-type MOSFET (M_p3). The drain terminal of M_n4 is connected to the drain terminal of M_p3 and the source terminal of M_n4 is connected to the ground line. The source terminal of M_p3 is connected to the power line and the gate and drain terminal of M_p3 are connected with each other. The size of M_n4 is the same as the size of M_n3. The gate width of M_p3 is twice larger than that of M_p1, or M_p2. The gate terminal and drain terminal of M_p3 are connected to the gate terminals of M_p1 and M_p2 in DIFF13110, respectively.
The switching circuit, SW_VGA 3120, has two input terminals (in_sw1, in_sw2), an output terminal (out_sw1), and a control terminal (cont_sw1). The control terminal cont_cell of VGA_cell 3101 is internally connected to the control terminal cont_sw1 of SW_VGA. The output terminal out_sw1 of SW_VGA 3120 is connected to the gate terminal of M_n4 in CM13130 and the gate terminal of M_n3 in DIFF13110. The input terminal in_sw1 of SW_VGA 3120 is connected to an external voltage source (V_vga). The input terminal in_sw2 of SW_VGA 3120 is connected to the ground line. Input terminal in_sw1 of SW_VGA 3120 is connected to output terminal out_sw1 of SW_VGA 3120 when a high logic signal is applied to control terminal cont_sw1 of SW_VGA 3120, and input terminal in_sw2 of SW_VGA 3120 is connected to output terminal out_sw1 of SW_VGA 3120 when a low logic signal is applied to control terminal cont_sw1 of SW_VGA 3120.
The voltage value of V_vga is determined so that the drain current of M_n3 can be a desired value (I_s1) when voltage value of V_vga is applied to the gate terminal of M_n3. The drain current of M_n4 is equal to that of M_n3 since their sizes are the same.
When a high logic signal is applied to control terminal cont_sw1 of SW_VGA 3120, V_vga is connected to the gate terminals of M_n3 in DIFF13110 and M_n4 in CM13130. Then, the drain currents of M_n3 and M_n4 are equal to I_s1. Also, the drain currents of M_p1 and M_p2 are equal to half of I_s1 since both of the gate widths of M_p1 and M_p2 are half of the gate width of M_p3, whose drain current is equal to I_s1. Accordingly, a differential output current of the VGA_cell is almost zero when the differential input signal is zero. When a differential input voltage, V_incell, is input to input terminals in_cell_p and in_cell_n of VGA_cell 3101, a differential output current from VGA_cell 3101, I_outcell, is expressed by the following equation 2.
I_outcell=(gm_cell)(V_incell) Equation 2
where gm_cell represents the gm value of M_n1 or M_n2.
When a low logic signal is applied to control signal cont_sw1 of SW_VGA 3130, the gate terminals of M_n3 in DIFF13110 and M_n4 in CM13130 are connected to the ground line. Accordingly, the output current from the VGA_cell 3101 is zero for any input signal applied to input terminals in_cell_p and in_cell_n of VGA_cell 3101.
The output current from VGA 310 is equal to the sum of the output currents from all VGA_cells 3101 in VGA 310. When a differential input voltage, V_invga, is input to in_vga of VGA, 310 a differential output current from VGA 310, I_outvga, is expressed as the following equation 3:
Iout—vga=(M—vga)(gm_cell)(V_invga) Equation 3
where M_vga represents the number of the VGA_cells 3101 for which a high logic signal is applied to the control terminal cont_cell. M_vga is a value controllable in the range from 1 to N by the control signal applied to control terminal cont_vga of VGA 310.
The VGA-controller 340 may include a variable-gain amplifier (VGA_dum) 3401, an envelope detector 3404, and a state machine 3406. The VGA-controller 340 has a differential input terminal (in_vgacont) and an N-bit output terminal (out_vgacont). The circuit configuration and operation of the VGA_dum 340 are the same as those of the VGA 310 shown in
The input terminal in_vgacont of the VGA-controller 340 is internally connected to the input terminal in_vga of VGA_dum 3401. The output terminal out_vga of VGA_dum 3401 is connected to the differential input terminal of the envelope detector 3404. The output terminal of the envelope detector 3404 is connected to the input terminal of the state machine 3406. The output terminal out_vgacont of VGA_controller 340 is internally connected to the output terminal of the state machine 3406 and the control terminal (cont_vga) of VGA_dum 3401.
The envelope detector 3404 acquires amplitude information of an input signal and outputs a DC value corresponding to the amplitude information. The output DC value of the envelope detector 3404 is input to the state machine 3406. The state machine 3406 outputs an N-bit logic signal corresponding to the input value by referring to a lookup table, and controls the gain of VGA_dum 3401 so that the amplitude of the VGA_dum 3401 output signal is approximately equal to the desired value.
The jammer generator 320 may include a comparator 3210, a signal period detector 3220 and a sine-wave generator 3230, and has a differential input terminal (in_gj), a differential− output terminal (out_gj), and external clock terminals {clk_c, clk_gen1, clk_gen2).
The comparator 3210 has a differential input terminal (in_com) and an output terminal (out_com). The signal period detector 3220 has an input terminal (in_spd), an output terminal (out_spd) and an external clock terminal (clk_spd). The sine-wave generator 3230 has an input terminal (in_sin), a differential output terminal (out_sin), a reset terminal (reset_sin) and two external clock terminals (clk_sin 1, clk_sin 2). Input terminal in_gj of the jammer generator 320 is internally connected to input terminal in_com of the comparator 3210. Output terminal out_com of the comparator 3210 is connected to input terminal in_spd of the signal period detector 3220 and reset_sin of the sine wave generator. Output terminal out_spd of the signal period detector 3220 is connected to input terminal in_sin of the sine-wave generator 3230. Output terminal out_gj, and clock terminals clk_c, clk_gen1 and clk_gen2 of the jammer generator 320 are internally connected to output terminal out_sin of the sine wave generator 3230, clock terminal clk_spd of the signal period detector 3220, and clock terminals clk_sin 1, and clk_sin 2 of the sine wave generator 3230, respectively.
The configuration and operation of the respective circuit blocks are described as follows.
The output voltage of the differential amplifier13211, Vout1, is expressed as in equation 4 below.
Vout1=−Av(Vin1−Vin2)+V0 Equation 4
where Av represents the gain of differential amplifier13211, Vin1 and Vin2 are the voltage values at in_com_p and in_com_n, respectively, and V0 is a voltage value as Vout1 under the condition that Vin1 and Vin2 are at the same values.
Inverter13212 outputs a voltage value (Vgg) approximately equal to the ground voltage when its input voltage is higher than its threshold voltage (Vth_inv). On the other hand, inverter13212 outputs a voltage value (Vdd) approximately equal to a supply voltage when its input voltage is lower than or equal to Vth_inv. The sizes of MN3 and MP3 are determined so that Vth_inv is approximately equal to V0.
When the comparator 3210 receives a sinusoidal signal as a differential input signal, differential amplifier13211 amplifies it according to equation 4. The output voltage of differential amplifier13211, Vout1′, is related to the differential input sinusoidal signal (A sin(ωt)) as in equation 5 below.
Vout1′=AvA sin(ωt)+V0 Equation 5
Considering that inverter13212 outputs Vgg (or Vdd) for an input voltage larger (or smaller) than V0, inverter1 outputs a rectangular signal with period of 2π/ω and duty cycle of 50% when receiving Vout1′ as an input signal.
The signal period detector 3220 may include a rising edge counter 3221 and a logic comparator 3222. The rising edge counter 3221 has an input terminal (in_counter), an output terminal (out_counter) and a reset terminal (reset_counter). The logic comparator 3222 has an input terminal (in_1c) and an output terminal (out_1c).
An input terminal, in_spd, of the signal period detector 3220 is internally connected to the reset terminal, reset_counter, of the rising edge counter 3221. A clock terminal, clk_spd, of the signal period detector 3220 is internally connected to the input terminal, in_counter, of the rising edge counter 3221. An output terminal, out_spd, of the signal period detector 3220 is internally connected to the output terminal, out_1c, of the logic comparator 3222. The output terminal, out_counter, of the rising edge counter 3221 is connected to the input terminal, in_1c, of the logic comparator 3222.
The rising edge counter 3221 outputs a logic value according to the counted number of rising edges at in_counter within two sequential rising edges at reset_counter. The logic comparator 3222 outputs a low logic value when a logic value at in_1c is larger than an internal preset logic value (c_logic), and outputs a high logic value when a logic value at in_1c is equal to or less than c_logic.
The sine wave generator 3230 may include a switch circuit (SW2) 3231, a digital-to-analog converter (DAC1) 3232 and a DAC-controller (DAC_cont) 3233.
The switch circuit SW23231 is similar to the switch circuit 3120 in VGA_cell 3101 illustrated in
The current value of CS_0 (I_CS_0) is expressed as below in equation 6.
I—CS—0=A sin(2π/80) Equation 6
where A is preset.
The other DAC cells that are cell_k (k=1, 2, . . . 19), have the same circuit topology as that of cell_0. Cell_k has two input terminals (inp_k, inn_k) and two output terminals (outp_k, outn_k) and may include two N-type MOSFETs (MN_dacp_k, MN_dacn_k) and a current source (CS_k). Inp_k and inn_k of cell_k are internally connected to gate terminals of MN_dacp_k and MN_dacn_k, respectively. Outp_k and outn_k of cell_k are internally connected to drain terminals of MN_dacp_k and MN_dacn_k, respectively. The source terminals of MN_dacp_k and MN_dacn_k are connected to each other and to CS_k.
The current value of CS_k (I_CS_k) is expressed as below in equation 7.
I—CS—k=A sin(2π(k+1)/80)−[I—CS_(k−1)+I—CS_(k−2)+ . . . +I—CS—0](1≦k≦19) Equation 7
where A is preset.
When both inp_k and inn_k receive a high logic value, MN_dacp_k and MN_dacn_k turn on, which makes cell_k output a current I_CS_k, with half of the current from outp_k and half of the current from outn_k. Therefore, a differential output current from cell_k is equal to zero. When inp_k (or inn_k) receives a low logic value and inn_k (or inp_k) receives a high logic value, a differential output current from cell_k is equal to I_CS_k (or −I_CS_k).
The differential output terminals (out_dac_p, out_dac_n) of DAC13232 are internally connected to the output terminals outp_k and outn_k in in all of cell_k (k=0, 1 . . . 19), respectively.
The differential output current from DAC13232 is equal to the sum of differential output currents form all of DAC cells, that is cell_k (k=0, 1, 2 . . . 19). DAC13232 can output a differential current, I_dac, expressed as below in equation 8 by varying a DAC code given to in_dac of DAC13232.
I—dac=A sin(2πj/80),where(0≦j≦79) Equation 8
When reset_dcont of the DAC controller 3233 receives a rising edge, the DAC controller 3233 outputs the DAC code to in_dac of DAC13232 so that the differential output current of DAC13232 is equal to I_dac with j=0 in the equation 9. And, when in_dcont of DAC controller 3233 receives a rising edge, DAC controller 3233 updates the DAC code so that the differential output current of DAC13232 changes in ascending order of j in equation 8. When j reaches 79, the DAC code is updated for j of 0 as a next step.
Assuming that the duration time of rising edges at in_dcont of the DAC controller 3233 is Tdiff, DAC13232 can output a pseudo sine wave signal with a period of Tdiff times 80.
The practical operation of the sine wave generator 3230 is described as below with reference to
Assume that clk_sin 1 and clk_sin 2 of the sine wave generator 3230 are connected to external clock sources with clock frequencies of Fclk1 and Fclk2, respectively. When in_sin of the sine wave generator 3230 receives a high logic value, the DAC controller 3233 updates the DAC code at a rate of Fclk1. Accordingly, DAC13232 outputs a pseudo sine wave signal with a period of 80/Fclk1. When in_sin of the sine wave generator 3230 receives a low logic value, the DAC controller 3233 updates the DAC code at a rate of Fclk2. Accordingly, DAC13232 outputs a pseudo sine wave signal with a period of 80/Fclk2.
A phase of the pseudo sine wave signal is reset to zero when reset_sin of the sine wave generator 3230 receives a rising edge.
The adder 330 has positive (+) differential input terminals in_pl_p and in_pl_n, negative (−) differential input terminals in_mi_p and in_mi_n, and differential output terminals out_ad_p and out_ad_n, and may include an operational amplifier (OP1) and two resistors, R_p and R_n. OP1 has differential input terminals in_op_p and in_op_n, and differential output terminals out_op_p and out_op_n. R_p and R_n may have the same resistance value, R_load.
The positive and negative differential input terminals of the adder 330 are internally connected to the differential input terminal of OP1. Positive differential input terminal in_pl_p and negative differential input terminal in_mi_n of the adder 330 are connected to the positive differential input terminal in_op_p of OP1, and positive differential input terminal in_pl_n and negative differential input terminal in_mi_p of the adder 330 are connected to the negative differential input terminal in_op_n of OP1. One terminal of R_p is connected to in_op_p and the other terminal of R_p is connected to out_op_n of OP1. One terminal of R_n is connected to in_op_n and the other terminal of R_n is connected to out_op_p of OP1.
Assume that a differential voltage gain (Avop) of OP1 is much larger than one (Avop>>1) and an input impedance of OP1 is also much larger than R_load.
A differential output voltage of OP1, Vout_op, is expressed as equation 9 below.
Vout—op=(Avop)(Vin—op), Equation 9
where Vin_op is a differential input voltage of OP1.
Vout_op is also expressed as below in equation 10 by Ohm's law.
Vout—op=Vin—op−R(Ipl−Imi) Equation 10
where I_pl and I_mi are, respectively, differential input currents from the positive differential input terminal and the negative differential input terminal of OP1.
From equations 9 and 10, Vout_op is calculated as in equation 11 below.
Vout—op=−Avop/(Avop−1)R(Ipl−Imi) Equation 11
Considering that Avop is much larger than one, Vout_op is approximately expressed as in equation 12 below.
Vout—op=−R(Ipl−Imi) Equation 12
Equation 12 indicates that the adder 330 outputs a differential voltage proportional to the difference between currents input to the positive differential input terminal and the negative differential input terminal of OP1.
The operation of this exemplary embodiment is described as follows.
As described before, many channel signals (Smulti) may be input to this exemplary embodiment simultaneously. Only one channel signal in Smulti is a desired signal (S1) and the other channel signals are all considered jammers. Here, we assume that the power of a specific jammer (J1) is higher by Pj1 dB than the summation of signal powers of any other channel signal including S1. We also assume that the modulation type of J1 is frequency-shift-keying (FSK) and its modulation index, frequency deviation, and carrier frequency are known as m, Fdiv (Hz), Fc (Hz) respectively. The ratio of Fc to Fdiv is defined as Fratio. A data rate, DRj1 is equal to Fdiv/m.
In addition, we assume that Pj1 is equal to 40 dB and J1 has a frequency of Fc+Fdiv/2 for representing the symbol “1” and a frequency of Fc−Fdiv/2 for representing the symbol “0”, and Fratio is larger than ten.
Referring to
The amplitude of J1 included in the VGA output current and the jammer generator's output current matches within an accuracy of about 1% since the power of J1 is 40 dB larger than the summation of the signal powers of any other channel signal. Accordingly, the amplitude of J1 included in the VGA output current is approximately equal to that of the pseudo sine wave signal current from the jammer generator 320.
The VGA output signal is transferred to the jammer generator 320. The input signal of the jammer generator 320 is internally transferred to the comparator 3210 (see
The comparator 3210 outputs a high logic value for its input voltage greater than zero and a low logic value for its input voltage less than or equal to zero.
The input signal of the jammer generator (Vin jam) can be expressed as in equation 13 below since a power of J1 is 40 dB larger than the summation of the other channel.
Vin_jamgen=B sin(2π/Tj1t)+Vother, Equation 13
where Vother is expressed by equation 14.
|Vother|<B10^(−Pj1/20)=0.01B, Equation 14
where B and Tj1 represent the amplitude and period of J1 included in the input signal of the jammer generator 320, respectively.
The time, T0, at which Vin_jamgen crosses a zero point in direction from negative to positive, is expressed as in equation 15 below.
T0=Tj1_only+Tother, Equation 15
where Tj1_only is expressed by equation 16.
Tj1_only=k(Tj1),where k=0,1,2, . . . Equation 16
and the Tother is expressed by equation 17.
|Tother|<(Tj1/2π)Arcsin(10^(−Pj1/20))=0.01Tj1/2π=0.0016Tj1 Equation 17
where Tj1_only represents the time at which the phase of J1 is equal to zero. Tother represents the degree by which the other channel signals affect Tj1.
Equations 15, 16, and 17 indicate that T0 matches with Tj1_only within an accuracy of about 0.16%.
This also indicates that the period of the output signal of the comparator matches with the period of J1 within an accuracy of about 0.16%.
The output signal of the comparator 3210 is transferred to the signal period detector 3220 in the jammer generator 320.
The operation of the signal period detector 3220 is described below with reference to
Referring to
When the output signal of the comparator 3210 is input to the signal period detector 3220, a logic value (Nclk) output from out_counter of the rising edge counter 3221 is determined as follows.
When the symbol of J1 is “1”:
Tj1 equals to 1/(Fc+Fdiv/2)
The duration of two sequential rising edges at reset_counter of the rising edge counter 3221 is 1/(Fc+Fdiv/2) as shown in
Nclk=Nclk1, Equation 18
where Nclk1 is an integer less than or equal to 1/(Fc+Fdiv/2)/Tclk.
When the symbol of J1 is “0”:
Tj1 equals to 1/(Fc−Fdiv/2)
The duration of two sequential rising edges at reset_counter of the rising edge counter 3221 is 1/(Fc−Fdiv/2) as shown in
Nclk=Nclk2, Equation 19
where Nclk2 is a maximum integer not more than 1/(Fc−Fdiv/2)/Tclk. Here, Tclk is set so that a difference between Nclk1 and Nclk2 is more than 1. It is noted that Nclk2 is always larger than Nclk1.
The output signal of the rising edge counter 3221 is transferred to the logic comparator 3222. By setting the internal preset logic value, c_logic, of the logic comparator 3222 to a value within Nclk1 and Nclk2, the logic comparator 3222 outputs a high logic value for its input of Nclk1 and a low logic value for its input of Nclk2.
Accordingly, the signal period detector outputs a high logic value for the J1 symbol of “1” and a low logic value for the J1 symbol of “0”. The output signal of the signal period detector is transferred to in_sin of the sine wave generator 3230. Reset_sin of the sine wave generator 3230 receives the output signal of the logic comparator 3210. Clk_sin 1 of the sine wave generator 3230 receives the clock signal from an external clock source with a frequency of (Fc+Fdiv/2)×80. Clk_sin 2 of the sine wave generator 3230 receives the clock signal from an external clock source with a frequency of (Fc−Fdiv/2)×80.
When the J1 symbol is “1”, in_sin of the sine wave generator 3230 receives a high logic value from the signal period detector 3220. Therefore, the sine wave generator 3230 outputs a pseudo sine wave signal with a frequency of Fc+Fdiv/2.
When reset_sin of the sine wave generator 3230 receives the rising edge, the phase of the pseudo sine wave signal is reset to zero. The time at which a rising edge is received by reset_sin of the sine wave generator 3230 is T0 in equation 15. Accordingly, the phase of the pseudo sine wave signal matches well with that of J1.
When the J1 symbol is “0”, the sine wave generator 3230 outputs a pseudo sine wave signal with a frequency of Fc−Fdiv/2. The phase of the pseudo sine wave signal also matches well with that of J1.
The above description indicates that the jammer generator 320 outputs a pseudo sine wave signal with the same frequency and phase as that of J1.
In addition, the amplitude of J1 at the VGA output signal is approximately equal to that of the jammer generator output.
Therefore, the amplitude, frequency and phase of the jammer generator output signal are approximately equal to those of J1 in the VGA output signal.
When the two differential input terminals of the adder 330 receive the VGA output signal and the jammer generator output signal, respectively, the adder 330 outputs a differential voltage proportional to the difference between the VGA output signal and the jammer generator output signal.
Given that the amplitude, frequency and phase of the jammer generator output signal are approximately equal to those of J1 in the VGA output signal, the power of J1 is greatly reduced at the adder output.
Therefore, this exemplary embodiment can improve the SNR by suppressing a jammer, resulting in the mitigation of the requirement for increased ADC resolution.
Second Exemplary Embodiment
The filtering circuit 400 of the second exemplary embodiment may include a voltage-current converter (VIC) 410, a variable amplitude jammer generator (VAJG) 420, an adder 430, and an amplitude controller 440.
The VIC 410 converts a voltage signal into a current signal with a preset conversion gain. The VAJG 420 identifies the frequency and phase of its input signal and then outputs a sinusoidal current with the same frequency and phase as the input signal. In addition, the amplitude of the sinusoidal current output from VAJG 420 may be controlled by an external control signal. The amplitude controller 440 adjusts the amplitude of the VAJG output current so that the amplitude of the output current of the VAJG 420 is equal to that of the VIC output current. The adder 430 may be the same circuit as the adder 330 described in the first exemplary embodiment (see
The input terminal of the filtering circuit 400 is internally connected to the input terminals of the VIC 410 and the amplitude-controller 440. The output terminal of the VIC 410 is connected to the input terminal of the VAJG 420 and the positive terminal of the adder 430. The output terminal of the amplitude-controller 440 is connected to the control terminal of the VAJG 420. The output terminal of the VAJG 420 is connected to the negative terminal of the adder 430. The output terminal of this exemplary embodiment is internally connected to the output terminal of the adder 430.
Here, we assume that Smulti, described in the first exemplary embodiment, is input to the filtering circuit 400 and the power of a specific Jammer (J1) is higher by Pj1 dB than the summation of the powers of any other channel signal including the desired signal (S1). And we also assume that the modulation type of J1 is frequency-shift-keying (FSK) and its modulation index, frequency deviation, and carrier frequency are known as m, Fdiv (Hz), Fc (Hz), respectively.
Input signal Smulti for this embodiment is processed in the VIC 410 so as to convert the voltage signal to a current signal, and the current signal is transferred to the input terminal of the VAJG 420 and the positive terminal of the adder 430. The VAJG 420 identifies the information of the frequency and phase of J1 in Smulti and outputs a sinusoidal current with the same frequency and phase as J1. This sinusoidal current is input to the negative terminal of the adder 430. The amplitude-controller 440 identifies the amplitude of J1 in Smulti and controls the amplitude of the sinusoidal current output from the VAJG 420 so that the amplitude of the VAJG's output sinusoidal current may agree with that of VIC output current. Accordingly, J1 at the positive terminal of the adder 430 agrees well with the sinusoidal wave at the negative terminal of the adder 430 in amplitude, frequency and phase. Therefore, only J1 in Smulti may be strongly suppressed at the output terminal of the adder 430.
The configuration and operation of the respective circuit blocks except for the adder 440, since it may be the same with that in the first exemplary embodiment, are described as follows.
The VIC 410 may include a differential amplifier (DIFF2) and a current mirror circuit (CM2). DIFF2 and CM2 may have the same configuration with DIFF1 and CM1 shown in
The circuit elements in VIC 410 which are the same with those shown in
Referring again to
When a differential input voltage, V_invic, is input, a differential output current from VIC 410, I_outvic, is expressed by equation 20.
Ioutvic=(gm—vic)(V_invic) Equation 20
where gm_vic is the gm value of M_n1, or M_n2.
The VAJG 420 may include a comparator 4210, a signal period detector 4220 and an amplitude variable sine-wave generator 4230. The VAJG 420 corresponds to the jammer generator 320 of the first exemplary embodiment in which sine-wave generator 3230 is replaced by the variable amplitude sine-wave generator 4230. The variable amplitude sine-wave generator 4230 corresponds to the sine wave generator 3230 of the first exemplary embodiment whose output amplitude can be controllable. The VAJG 420 has a control terminal (cont_gj) for adjustment of the output current amplitude in addition to terminals which are included in the jammer generator 320 of the first exemplary embodiment.
The output current, I_CSv_k, of the variable current source CSv_k is expressed as equations 21 and 22 below.
I—CSv—0=(Avcs—dac)sin(2π/80),where k=0 Equation 21
I—CSv—k=(Avcs—dac)sin(2π(k+1)/80)−[I—CSv_(k−1)+I—CSv_(k−2)+ . . . +I—CS—0],where 1≦k≦19 Equation 22
where Avcs_dac is preset and changeable by a control signal applied to cont_dac.
The DAC controller24233 controls the output current of VCS-DAC 4232, I_dacv, as expressed in equation 23 below by using the control table shown in
I—dacv=(Avcs—dac)sin(2π/80),where(0≦j≦79) Equation 23
Cont_sin of the variable amplitude sine-wave generator 4230 is internally connected to cont_dac of VCS-DAC 4232. Moreover, Cont_gj of VAJG 420 is internally connected to cont_sine of the amplitude variable sine-wave generator 4230. Therefore Avcs_dac in equation 23 can be controlled by the control signal given to cont_gj of VAJG 420. Accordingly, the amplitude of pseudo sine wave signal from the VAJG 420 can be controlled by the control signal applied to cont_gj of the VAJG 420.
The amplitude controller 440 has a differential input terminal in ac and an output terminal out_ac. VIC2441 and EV2442 may have the same configuration as VIC 410 shown in
A voltage signal input to the amplitude controller 440 is converted to a current signal at VIC2441 and the current signal is input to EV2442. EV2442 acquires amplitude information of the input signal and outputs a DC value corresponding to the amplitude information. The output DC value of the envelope detector 442 is input to ST2443. ST2443 outputs a control signal corresponding to the input value by referring to a lookup table so that the amplitude of the output signal of VAJG 420 is approximately the same as that of VIC2441.
Here, VIC 410 and VIC2441 have the same configuration and their input terminals are connected with each other. Therefore, the amplitude of the output current of VIC 410 is equal to that of VIC2441. Accordingly, the amplitude of the output current of VIC 410 is also equal to that of VAJG 420.
The frequency and phase of VAJG output current is approximately equal to that of VIC 410.
Therefore, the amplitude, frequency and phase of the VAJG output signal are approximately equal to those of J1 in VIC output signal.
When the two differential input terminals of the adder 430 receive the VIC output signal and the VAJG output signal, respectively, the adder 430 outputs a differential voltage proportional to the difference between the VIC output signal and the VAJG output signal.
Given that the amplitude, frequency and phase of the VAJG output signal are approximately equal to the amplitude, frequency and phase of J1 in the VIC output signal, the power of J1 is greatly reduced at the adder 430 output.
Therefore, the second exemplary embodiment can improve the SNR by suppressing a jammer, resulting in the mitigation of the resolution requirement for the ADC.
Exemplary embodiments of the invention also provide a method of detecting a desired signal in the presence of jammer signals.
As shown in
As shown in
As shown in
While the embodiments of the present invention have been described, additional variations and modifications of the embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, it is intended that the appended claims shall be construed to include both the above embodiments and all such variations and modifications that fall within the spirit and scope of the invention.
This application is a divisional of U.S. patent application Ser. No. 12/432,196, filed Apr. 29, 2009, the contents of all of which are incorporated herein by reference in their entirety.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3896262 | Hudspeth et al. | Jul 1975 | A |
| 20030224723 | Sun et al. | Dec 2003 | A1 |
| 20090190633 | Smith | Jul 2009 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20120231724 A1 | Sep 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12432196 | Apr 2009 | US |
| Child | 13477552 | US |
