This invention relates to, an envelope detector, an amplifier circuit, a wireless communication unit and a method for detecting a modulation envelope.
Amplifiers are generally known in the art. For example, power amplifiers are widely used in wireless transmission systems to amplify a signal such that the signal has sufficient energy to be transmitted via an antenna. However, often the performance is limited by the non-linear behaviour of the Power Amplifier (PA). To obviate the non-linear behaviour of the PA, various techniques are known, such as predistortion and envelope injection techniques.
For example Chi-Shuen et al. “A New Approach to Amplifier Linearization by the Generalized Baseband Signal Injection Method”, IEEE Microwave and Wireless Components Letters, VOL. 12, No 9, pp 336-338. September 1999 discloses a circuit which determines a base-band signal from an input signal, and injects the base-band signal into a power amplifier. The circuit further injects the base-band signal into a diode predistorter, which is connected to the amplifier as well. The circuit includes a coupler by means of which a combined capacitive and inductive connection to a signal path is established, in order to receive the input signal. The coupler is connected to the gate of a MESFET, which acts as a low frequency detector. The output of the MESFET is transmitted to respective operational amplifiers (opamps). Each of the opamps provides an amplified signal to a corresponding quarter wavelength phase-shifter. The quarter wavelength phase shifters are connected to the diode predistorter and the amplifier, respectively.
However, a disadvantage of this circuit is that it consumes a significant amount of power and leads to a trade off between linearity and power added efficiency (PAE). Furthermore, it is difficult to implement as an integrated circuit, because the operational amplifiers are typically manufactured with a different kind of process than the power amplifier. Also, the circuit has a large footprint because the coupler occupies a large amount of space.
The present invention provides an envelope detector, a linearization circuit, an amplifier circuit, a wireless communication unit and a method for detecting a modulation envelope as described in the accompanying claims.
Specific embodiments of the invention are set forth in the dependent claims.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings.
FIG. 3| shows a block diagram of an example of an embodiment of a wireless communication unit.
Although in the following an example of an embodiment will be described which forms an amplifier circuit, it should be noted that the invention may be implemented in any other type of electronic circuit and the invention is not limited to applications in amplifier circuits. Referring to
The linearizer 16 may, as shown in
The envelope detector 100 may operate as follows. The sensor 102 may sense a parameter which forms a measure for the amount of electrical power presented at the sensor input 1021. The sensor 102 may for example sense the current transmitted along an electrical path 14 to which the sensor input 101 is connected via an electrically conducting connection. As for instance shown in the example of
As shown in the example of
The sensor 102 may be implemented in any manner suitable for the specific implementation. The sensor 102 may generate, from the inputted signal, a signal which can be inputted in the filter 103 and which includes information about the envelope of the modulated signal.
The sensor 102 may for example include a current sensor for sensing the amount of current flowing through the electrical path 14. The amplifier may have for example a current output. Without wishing to be bound to any theory, since for a current output the voltage at the current output is constant, e.g. determined by the power source Vs of the amplifier, the current forms a measure for the outputted amount of power. To sense the current, the sensor 102 may for example be connected with the sensor input 1021 to a node 15 of the electrical path 14, and a part of the electrical power flowing through the electrical path 14 may be fed to the sensor 102 via the sensor input 1021. Referring to the example shown in
For instance, in the example of
The active electrical device T2 be any suitable type of device. The active electrical device may for example include an controllable current source which is connected with a current input to the electrical path 14, such as a bipolar transistor (BT) such as a Heterojunction Bipolar Transistor (HBT), a field effect transistor or other controllable current source. The active electric device may for example be of a type similar to an active device which outputs the modulated signal. For example, as shown in
As shown in
The sensor 102 may include a current control input 106 at which a signal may be presented which controls the current drawn by the active device source. As for instance shown in the example of
The amplitude control signal may for example be the same signal as an input signal presented to a device to which the modulated signal is presented or by which the modulated signal is outputted. As is explained below in more detail, for example, the amplitude control signal may be a modulated signal inputted to an amplifier 10, or other device, to which the envelope signal is inputted, be processed, e.g. amplified, together with the modulated signal. Thereby, the modulation distortion incurred in the electronic device due to non-linear behaviour can be reduced.
The active electrical device T2 may be arranged to control at least the amplitude of the current signal based on the amplitude control signal. In case, as for instance shown in
As shown in
The sensor 102 may as shown in
The envelope detector 100 may consist of passive components and transistors only. Thereby, the envelope detector 100 may be especially suited for implementation in a single integrated circuit. Furthermore, the components of the envelope detector 100 may be manufactured in the same process as an amplifier, and accordingly may thereby be implemented in the same integrated circuit as the amplifier 10. As for example shown in
Between sensor input 1021 and the active device T2, a power limiter may be present. The power limiter may limit the amount of power inputted to the sensor 102, to prevent a power overload of the components in the sensor 102. For example, in case the sensor 102 includes an active device T2, operation of the active device T2 in a desired region may be ensured. For example, in case the active device T2 includes a BT, such as a HBT, the collector current Ic may degrade when the amount of power transmitted over the electrical path 14, and hence the sensed signal, exceeds a threshold. For example, without wishing to be bound to any theory, it has been found that at a Power Amplifier output power of 15 dBm or more the collector current of a HBT might deteriorate due to the negative swing of the collector current.
The power limiter may for example an RC network between the sensor 102 and the detector input 101. For instance in the example of
The envelope detector 100 may include a phase shifter for shifting the phase of the envelope signal relative to the modulated signal. The envelope detector 100 may include a phase shifter 107 The phase shifter 107 may, for example, shift the phase of the sensed signal or the envelope modulation signal, for example to have the envelope modulation signal match phase requirements imposed by the application of the envelope detector 100. For instance, as explained below in more detail the envelope detector may be used to reduce inter modulation distortion (IMD) by injecting the envelope signal into a device which processes the modulated signal, and the phase shifter may adjust the phase of the respective signal to ensure that the injected envelope signal has a phase which reduces the distortion components in the signal.
The phase shifter may be implemented in any manner suitable for the specific implementation. In the example of
The filter 103 may be implemented in any manner suitable for the specific implementation. The filter may be connected with a filter input 1031 to the sensor 102, to receive the sensed signal. The filter 103 may remove from the sensed signal undesired signal components, and more in particular remove RF frequency components not included in the modulation envelope of the signal. The filter 103 may for instance remove components such as the carrier or other non-envelope components such as intermodulation products from the sensed signal. The filter 103 may for example include a low-pass filter. The filter 103 may for example be an active filter or be a passive filter, such as a LC filter or, as for instance in the example of
The passive, low-pass filter may for example include a series RC-circuit which low-pass filters a voltage signal presented at a filter input 1031. The low-pass filter may have a cut-off frequency below the carrier frequency of the modulated signal and above the frequency fenv of the modulation envelope. For example, without wishing to be bound to any theory the low-pass filter is found to effectively function with fenv<fcut-off<N·fenv and N being equal or larger than 3. For example, the cut-off frequency may be equal or larger than 200 KHz, such as 1.1 MHz or more, for example 4 MHz or more. the cut-off frequency may be lower than 2 GHz, such as lower than 800 KHz for example. As shown in
The envelope detector 100 may output the modulation envelope signal at an output 104 to other device. The output 104 may be connected to a capacitor C6 which reduces the DC level of the signal provided to the output 104. For example, the capacitor C6 may remove the DC off-set caused by the filter 103 such that the signal presented at the output 104 has a DC level of about zero.
The envelope detector 100 may be provided in any suitable device, for example in a demodulator or other suitable device. As shown in
As shown in
In the example of
The device may for example be an amplifier 10. The amplifier 10 may be any suitable type of amplifier. The amplifier 10 may for example be a power amplifier, such as an RF power amplifier. As shown in the example of
The envelope detector 100 may for instance be present in a feedforward loop or in a feedback loop. As shown in
As shown in
f
M,N
=M·f1±N·f2, where M, N=0, 1, 2, 3, . . . (1)
With fM,N representing the frequency. The order of the distortion product is given by the sum of M and N. Accordingly, the second-order inter-modulation products of two signals at f1 and f2 would occur for {M=1, N=−1}, {M=−1, N=1}, and hence at f1−f2 and f2−f1. In this respect, it should be noted that the harmonic components of the input signals f1 and f2, such as 2·f1, 2·f2, 3·f1, 3·f2, etc. are not considered as intermodulation products.
Third order inter-modulation products of the two signals, f1 and f2, would be at frequencies: 2·f1+f2, 2·f1−f2, f1+2·f2, f1−2·f2. Where 2·f1 is the second harmonic of the signal at frequency f1 and 2·f2 is the second harmonic of the signal at frequency f2. Of these frequencies, only the frequencies 2·f1−f2 and 2·f2−f1 are commonly referred to as the third order inter-modulation (IMD3) products, since typically the frequencies 2·f1+f2 and f1+2·f2 are outside the carrier band. For example, for most types of modulated signals, such as amplitude modulated signals, frequency modulated signals, phase modulated signals, the spectrum of the modulated signal includes frequencies f1 and f2 which are related to each other by f1=fcarrier−fenv and f2=fcarrier−fenv where fenv is the envelope frequency. Typically the carrier frequency fcarrier is (much) larger than the envelope frequency fenv. Accordingly, f1 and f2 are relatively close to each other, and the third order terms 2·f1−f2 and 2·f2−f1 will be close to f1 and f2 as well. Accordingly, a regular band-pass filter will not remove the IMD3 since the IMD3 components are within the pass-band of the filter. To reduce the third order modulation, the envelope of the signal can be injected into the, non-linear, electronic device, with suitable amplitude and phase shift relative to the phase of the inter-modulation product to be reduced.
In the example of
The envelope detector 100 may for example be connected with the input 1021 of the sensor 102 to the electrical path 14 downstream of the amplifier output RFout. The envelope detector output 104 may for example be directly or indirectly connected to an input of the amplifier output stage 11. The amplifier circuit may for instance include a bias source 140 connected to a bias input 113 of a respective stage 11-13 of the amplifier circuit 1. The bias source 140 may, as shown in
The amplifier circuit 1 may be used in any suitable type of device or apparatus. For instance, the amplifier 10 may be used in a wireless communication unit, for example to amplify a RF signal to an amplifier signal suitable to be transmitted by an antenna over a wireless connection. The wireless communication unit may for example include a signal generator, an amplifier circuit 1 and an antenna. The signal generator may generate a signal and transmit the generated signal to the amplifier 10. The amplifier 10 may amplify the generated signal such that the signal contains a sufficient amount of energy to be converted into an electromagnetic wave via the antenna and transmit the amplified signal to the antenna.
For instance,
The user interface 209 may be connected to a memory unit 206 and a timer 204, for instance via the signal processor 208 and/or a controller 205. The controller 205 may also connected to the receiver front-end circuit 203 and the signal processor 208. The controller 205 may for example receive bit error rate (BER) or frame error rate (FER) data from recovered information. The controller 205 is connected to the memory device 206 for storing operating regimes, such as decoding/encoding functions and the like. A timer 204 may be connected to the controller 205 to control the timing of operations (transmission or reception of time-dependent signals) within the wireless communication unit 200.
As regards the transmit chain 220, the input device 210 may be connected to a modulator circuit 207, for instance via the signal processor 208. The input device 210 may generate a transmit signal and transmit the signal to the modulator circuit 207. The transmit signal may be processed between generation and reception by the transmitter/modulation circuit, and for example be subjected to an analog-to-digital conversion, be converted into packets of data or other suitable processing by the signal processor 208. The transmitter/modulation circuitry 207 and receiver front-end circuitry 203 comprise frequency up-conversion and frequency down-conversion functions (not shown). The transmitter/modulation circuit 207 may modulate the transmit signal into a modulated signal and pass the, envelope modulated, transmit signal to a power amplifier 10 to be radiated from the antenna 201. The modulator circuit 207 and the power amplifier 10 are operationally responsive to the controller 205, with an output from the power amplifier 10 connected to the duplex filter or antenna switch 202. As shown in
In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. For example, the transistors shown in
Also, the invention is not limited to physical devices or units implemented in non-programmable hardware but can also be applied in programmable devices or units able to perform the desired device functions by operating in accordance with suitable program code. Furthermore, the devices may be physically distributed over a number of apparatuses, while functionally operating as a single device. For example, the envelope detector may include two or more discrete semiconductor components. E.g. the sensor 102 and the filter 103 may be implemented as separate integrated circuits.
Also, devices functionally forming separate devices may be integrated in a single physical device. For example, the amplifier circuit may for example be implemented as a single monolithic integrated circuit, for example manufactured using a RF Complementary Metal Oxide Silicon (RF CMOS), merged CMOS and bipolar (Bi-CMOS), a SiGe, or a GaAs process. However, the invention is not limited to an integrated circuit or a particular topology or a specific device technology.
However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.
In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the words ‘a’ and ‘an’ shall not be construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB06/54688 | 10/23/2006 | WO | 00 | 12/1/2009 |