Patent Application
20070243845
The invention will be described in detail with reference to the following drawings in which like numerals refer to like elements.
Preferred embodiments of the present invention will be described in a more detailed manner with reference to the drawings.
Hereinafter, a balun apparatus in accordance with the present invention and a receiver comprising the same will be described in detail with reference to the drawings in accordance with an embodiment of the present invention.
As shown in
The input terminal of the passive unit 310 is connected to a first node {circle around (1)}, the in-phase output terminal of the passive unit 310 is connected to a second node {circle around (2)}, and the inverse-phase output terminal of the passive unit 310 is connected to a third node {circle around (3)}.
The input terminal of the first active unit 320 is connected to a first node {circle around (1)}, and the output terminal of the first active unit 320 is connected to a second node {circle around (2)}.
The input terminal of the second active unit 330 is connected to a first node {circle around (1)}, and the output terminal of the second active unit 330 is connected to a third node {circle around (3)}.
An input signal (single-ended: VIN) is applied to a first node {circle around (1)}. An in-phase signal VOUT+ is taken at a second node {circle around (2)}, and an inverse-phase output signal VOUT− is taken at a third node {circle around (3)}.
The passive unit 310 receives the input signal VIN and outputs an in-phase signal 322 that has an identical phase compared to the input signal VIN.
The first active unit 320 receives the input signal VIN and outputs an in-phase compensating signal 321 that has an identical phase compared to the input signal VIN.
The in-phase compensating signal 321 is a signal for compensating the loss of the in-phase signal 322 caused by the passive unit 310. The in-phase compensating signal 321 has an identical phase and different amplitude compared to the in-phase signal 322.
According to the structure described above, the in-phase output signal VOUT+ is formed by adding the in-phase signal 322 of the passive unit 310 applied to a second node {circle around (2)} and the in-phase compensating signal 321 of the first active unit 320 applied to a second node {circle around (2)}.
The passive unit 310 receives the input signal VIN and outputs an inverse-phase signal 332 that has an inversed phase compared to the input signal VIN.
The second active unit 330 receives an input signal VIN and outputs an inverse-phase compensating signal 331 having an inversed phase compared to the input signal VIN.
The inverse-phase compensating signal 331 is a signal for compensating the loss of the inverse-phase signal 332 caused by the passive unit 310. The inverse-phase compensating signal 331 has an identical phase and different amplitude compared to the inverse-phase signal 332.
According to the structure described above, the inverse-phase output signal VOUT− is formed by adding the inverse-phase signal 332 of the passive unit 310 applied to a third node {circle around (3)} and the inverse-phase compensating signal 331 of the second active unit 330 applied to a third node {circle around (3)}.
That is, the first active unit 320 and the second active unit 330 behaves as a balanced circuit that simultaneously receives the input signal VIN, differentially amplifies them and outputs the in-phase compensating signal 321 and the inverse-phase compensating signal 331.
The internal circuits of the passive unit 310, the first active unit 320 and the second active unit 330 will be described in detail with reference to
As shown in
Hereinafter, the structure of the hybrid balun apparatus 300 according to the present embodiment will be described.
The passive unit 310 comprises a transformer 311 and a fifth capacitor C33 for bypassing AC (alternating current) signal.
The transformer 311 comprises a primary coil and a secondary coil. A center tap terminal is formed at the middle of the second coil for balanced output signals.
The first active unit 320 comprises a first transistor NM3a and a first capacitor C31+.
The second active unit 330 comprises a second transistor NM3b and a second capacitor C31−.
The hybrid balun apparatus 300 comprises a third capacitor C32+ for removing the DC (direct current) component of the in-phase output signal VOUT+, a fourth capacitor C32− for removing the DC component of the inverse-phase output signal VOUT−, and a fifth capacitor C33 for bypassing AC component from the tap terminal of the transformer 311 to the ground.
Hereinafter, the connecting relations of constitutional elements in the hybrid balun apparatus 300 according to the present embodiment will be described.
The one end of the primary coil of the transformer 311 is connected to a first node {circle around (1)}, and the other end of the primary coil is connected to the ground. The in-phase output terminal of the secondary coil of the transformer 311 is connected to a second node {circle around (2)}, and an inverse-phase output terminal of the secondary coil is connected to a third node {circle around (3)}. The center tap terminal of the inverse-phase output terminal is connected to a sixth node {circle around (6)}.
The one end of the fifth capacitor C33 is connected to a sixth node (, and the other end of the fifth capacitor C33 is connected to the ground.
The one end of the first capacitor C31+ is connected to a first node (, and other end of the first capacitor C31+ is connected to a fourth node (.
The gate terminal of the first transistor NM3a is connected to a fourth node {circle around (4)}. A power supply voltage VDD is connected to the drain terminal of the first transistor NM3a, and the source terminal of the first transistor NM3a is connected to a second node {circle around (2)}.
The one end of a third capacitor C32+ is connected to a second node {circle around (2)}, and the other end of the third capacitor C32+ outputs an in-phase output signal VOUT+.
The one end of a second capacitor C31− is connected to a first node {circle around (1)}, and the other end of the second capacitor C31− is connected to a fifth node 5.
The gate terminal of the second transistor NM3b is connected to a fifth node 5. The drain terminal of the second transistor NM3b is connected to a third node {circle around (3)}, and the source terminal of the second transistor NM3b is connected to the ground.
The one end of the fourth capacitor C32− is connected to a third node {circle around (3)}, and the other end of the fourth capacitor C32− outputs an inverse-phase output signal VOUT−.
Hereinafter, the operations of the hybrid balun apparatus 300 according to the present embodiment will be described with reference to
When an input signal VIN is applied to a first node {circle around (1)}, the supplied input signal VIN is applied simultaneously to the input terminal of the passive unit 310, the input terminal of the first active unit 320, and the input terminal of the second active unit 330.
When the input signal is applied to the one end of the primary coil of the transformer 311 of the passive unit 310, the secondary coil that is magnetically coupled to the primary coil becomes excited, and the output signal is generated at the secondary coil.
Therefore, the transformer 311 outputs the in-phase signal 322 that has an identical phase compared to the input signal VIN to a second node {circle around (2)} through the in-phase output terminal of the secondary coil along an in-phase signal path 322a.
Also, the transformer 311 outputs an inverse-phase signal 332 that has an inverse phase compared to the input signal VIN to the third node {circle around (3)} through an inverse-phase output terminal of the secondary coil along an inverse-phase signal path 332a.
However, the transformer 311 usually causes signal power loss during the signal conversion process from the single-ended input signal VIN to the differential signals 322 and 332.
The transformer 311 has such a characteristic because a coupling coefficient (k-factor) of the transformer 311 is typically less than 1.
In order to overcome such a drawback, the hybrid balun apparatus 300 according to the present embodiment comprises the first active unit 320 for generating an in-phase compensating signal 321 that compensates the in-phase signal 322 of the transformer 311, and a second active unit 330 for generating an inverse-phase compensating signal 331 that compensates the inverse-phase signal 332 of the transformer 311.
The first active unit 320 removes the DC component of the input signal VIN applied to the input terminal of the first active unit 320 by using the first capacitor C31+.
The DC-removed input signal VIN is applied to the gate terminal of the first transistor NM3a along the in-phase compensating signal path 321a. And the in-phase compensating signal 321 is generated with an identical phase and a smaller amplitude compared to the input signal VIN, and supplied to the second node {circle around (2)}.
That is, the in-phase output signal VOUT+ is formed of the sum of the in-phase signal 322, which is provided through the in-phase signal path 322a of the passive unit 310, and the in-phase compensating signal 321, which is provided through the in-phase compensating signal path 321a of the first active unit 320.
According to the structure described above, the loss of the input signal VIN at the passive unit 10 is compensated by the first active unit 320 in the hybrid balun apparatus 300 according to the present embodiment.
Using same method, the second active unit 330 removes the DC component of the input signal VIN supplied to the input terminal of the second active unit 330 by using the second capacitor C31−.
The DC-removed input signal VIN is applied to the gate terminal of the second transistor NM3b along the inverse-phase compensating signal path 331a. And the inverse-phase compensating signal 331 is generated with an inverse-phase and a smaller amplitude compared to the input signal VIN, and supplied to the third node {circle around (3)}.
That is, the inverse-phase output signal VOUT− is formed of the sum of the inverse-phase signal 332, which is provided through the inverse-phase signal path 332a of the passive unit 310, and the inverse-phase compensating signal 331, which is provided through the inverse-phase compensating signal path 331a of the second active unit 330.
According to the structure described above, the loss of the input signal VIN at the passive unit 310 is compensated by the second active unit 330 in the hybrid balun apparatus 300 according to the present embodiment.
Also, the hybrid balun apparatus 300 according to the present embodiment has less power consumption, wideband characteristic, and better linearity compared to the conventional active balun due to its simple circuit structure and no resonating element. Also, the hybrid balun apparatus 300 according to the present embodiment has higher power gain and lower noise factor compared to the conventional passive balun due to the active compensating parts.
Also, the first active unit 320 and the second active unit 330 can be embodied as a fully symmetric differential amplifier circuit that provides the in-phase compensating signal 321 and the inverse-phase compensating signal 331 by differentially amplifying the input signal VIN.
Table 1 compares the characteristics of a passive balun circuit and a hybrid balun apparatus 300 according to the present invention.
Table 1 shows the representative results of prototype measurements of a hybrid balun according to the present embodiment that is manufactured using a 0.18 μm radio frequency (RF) complementary metal-oxide semiconductor (CMOS) manufacturing process. As shown in Table 1, the hybrid balun apparatus according to the present invention has about 0.57 dB amplitude error and about 1.93° phase error at 2.4 GHz. The gain of the hybrid balun is improved as much as about 3.2 dB, and the noise factor is improved as much as about 0.35 dB compared to the conventional passive balun.
Also, the hybrid balun apparatus 300 according to the present embodiment consumes about 0.68 mA at about 1.2V, and the overall power consumption is about 0.82 mW.
A bias voltage VBIAS+ is supplied to the gate terminal of the first transistor NM3a which is a fourth node {circle around (4)}, and a bias voltage VBIAS− is supplied to the gate terminal of the second transistor NM3b which is a fifth node {circle around (5)}.
As shown in
The third capacitor C32+ blocks the DC not to be included in the in-phase output signal VOUT+, and the fourth capacitor C32− blocks the DC not to be included in the inverse-phase output signal VOUT−.
The fifth capacitor C33 is used for AC-ground for RF signals.
The DC bias current flows through the first transistor NM3a and the second transistor NM3b. Since the bias current flows along the current path 312, the DC current is reused by the first active unit 320 and the second active unit 330.
As shown in
Table 2 compares the overall noise factors and gains of a receiver 400 comprising the hybrid balun apparatus 410 shown in
As shown in Table 2, the hybrid balun apparatus 410 improves the overall noise factor of the receiver as much as about 1.8 dB and the overall gain of the receiver as much as 3.2 dB.
Therefore, the improvement of the noise factor significantly improves the receiving sensitivity of the receiver.
As described above, the hybrid balun apparatus provides very symmetric differential outputs over a wideband, consumes less DC power, lowers the noise factor, enhances the signal gain, and hardly suffers the linearity problems according to the structure of the present invention.
Also, the receiving band of the balun apparatus becomes broader compared to the conventional active balun apparatus.
Furthermore, if the balun apparatus according to the present invention is applied into the receiver, the overall noise factor is lowered, the overall signal gain is improved, the DC power consumption is reduced, and the receiving band becomes wider.
The foregoing exemplary embodiments and aspects of the invention are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0035056 | Apr 2006 | KR | national |
