# Patent

## Title
Self-calibrating direct conversion transmitter with converting/steering device

## Abstract

A converting/steering device has a normal mode and a calibration mode. The converting/steering device includes a merged mixer/VGA and a mode controller. The merged mixer/VGA has a mixing stage and an amplifying stage. In the normal mode, the mode controller deactivates the mixing stage of the merged mixer/VGA, and the device operates as an RF VGA. In the calibration mode, the mode controller activates the mixing stage of the merged mixer/VGA and passes a local oscillator signal to the mixing stage, so that the device operates as a down-mixer.

## Background
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a direct conversion transmitter (DCT), more particularly, to a merged down-mixer and radio frequency (RF) variable gain amplifier (VGA) used in the direct conversion transmitter.
BACKGROUND OF THE INVENTION
Direct conversion transmitters are widely used in the field of wireless communication. In a direct conversion transmitter, baseband in-phase (I) and quadrature-phase (Q) signals are up-converted into radio frequency (RF) signals with a carrier provided by a local oscillator. Then the up-converted I signal and Q signal are then summed, amplified as an output signal and the output signal is transmitted via an antenna.
Carrier leakage caused by local oscillator error, baseband mismatch etc. is a concerned issue for the direct convention transmitter. To eliminate or reduce carrier leakage, a common solution is to detect an output of the direct conversion transmitter when no I and Q signals are input thereto, so as to obtain the leakage, and generate a compensation signal based on the detected leakage, led to reduce or even eliminate the leakage. The detection and compensation procedures can be repeated until the leakage is minimized.
For some applications, such as WCDMA, it is necessary to provide an RF variable gain amplifier (VGA) on a signal output path of the direct conversion transmitter to adjustably generate an output signal with a variable gain under a transmission condition. Further, under a calibration condition, before detecting the output signal for leakage upon no I and Q input signals fed into the transmitter, it is optimal to down-convert the leakage at radio frequency (RF) into a lowered frequency, such as an intermediate frequency (IF) or a baseband (BB) frequency for the convenience of process in the subsequent steps.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a converting/steering device for a direct conversion transmitter (DCT). The converting/steering device includes a merged mixer/variable gain amplifier (VGA) functioning as both a mixer and a VGA but occupying a smaller space.
The converting/steering device in accordance with the present invention operates as either an RF VGA while set at a normal mode (or called “transmission mode”), or a down-mixer while set at a calibration mode.
When the DCT is under a transmission condition, the merged converting/steering device is switched to the normal mode and functions as an RF VGA.
When the DCT is under a calibration condition, the merged converting/steering device is switched to the calibration mode and functions as a mixer for down-converting the leakage.
The converting/steering device is particularly advantageous for the wireless transmission application with the need for RF VGA.
Another object of the present invention is to provide a direct conversion transmitter with the converting/steering device.
In accordance with one aspect of the present invention, the merged mixer/VGA device of the converting/steering device includes a mixing stage having a transistor quad connected as a double balanced mixer and an amplifying stage having a transistor quad connected as an RF VGA. The mixing stage and amplifying stage are connected with each other in parallel. The converting/steering device further includes a mode controller for controlling DC biases for the mixing stage and amplifying stage of the merged mixer/VGA and the access of a local oscillator signal to the mixing stage, so as to switch the device into one of the normal mode and calibration mode.
In accordance with another aspect of the present invention, the direct conversion transmitter includes an up-converter for mixing an in-phase (I) baseband signal and a quadrature-phase (Q) baseband signal with an RF carrier signal to respectively generate RF I and Q signals, a summing device for combining the RF I and Q signals into a combined RF signal, wherein in the normal mode the converting/steering device adjusts the combined RF signal with a predetermined gain or in the calibration mode the converting/steering device receives and utilizes a local oscillator signal to down-convert the RF signal into a lowered-frequency signal, and a calibration processing unit for detecting the lowered-frequency signal from the merged converting/steering device, generating a compensation signal based on the detected lowered-frequency signal and incorporating the compensation signal into said I baseband signal and Q baseband signal to reduce or even eliminate the carrier leakage.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be further described in detail in conjunction with the accompanying drawings, wherein:
FIG. 1 is a block diagram schematically showing a direct conversion transmitter in accordance with the present invention;
FIG. 2 is a block diagram schematically showing the converting/steering device in FIG. 1;
FIG. 3 is a schematic circuit diagram of a merged mixer/VGA in accordance with an embodiment of the present invention;
FIG. 4 is a block diagram schematically showing the mode controller in FIG. 2; and
FIG. 5 is a schematic circuit diagram of a merged mixer/VGA in accordance with another embodiment of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram schematically showing a direct conversion transmitter in accordance with the present invention. FIG. 1 roughly illustrates only the essential elements for the sake of simplification and clarification.
When the direct conversion transmitter is under a transmission condition, an in-phase (I) baseband signal Ibb and a quadrature-phase (Q) baseband signal Qbb are up-converted into a radio frequency (RF) I and Q signals with an I component and Q component of a first local oscillator (LO) signal LO1 from an first local oscillator 20, respectively, by up-mixers 21 and 23. Then the RF I and Q signals are summed by a summing device 30 into a combined RF signal. The combined RF signal is adjusted with a variable gain by a converting/steering device 40 which is switched to a normal mode, and then is amplified by a power amplifier 60 and transmitted via an antenna 70.
When the direct conversion transmitter is under a calibration condition, no baseband signals Ibb and Qbb are input to the transmitter. A leakage signal, which may be generated due to the local oscillator 20 or other sources, is easy to be detected in this condition. The converting/steering device 40 is switched to a calibration mode and operates as a down-mixer to down-convert the leakage signal into a lowered frequency with a second local oscillator (LO) signal LO2 provided by a second local oscillator 50. It is noted that the first and second local oscillators 20, 50 can be combined as a single module in some applications. The LO signals LO1 and LO2 can be provided by any proper method. The down-converted leakage signal is then detected by a calibration detection/determination unit 81. Analog to digital conversion is preferably done after leakage-signal detection. The calibration detection/determination unit 81 determines and generates a compensation signal based on the detected leakage signal according to a calibration algorithm stored therein.
Any proper calibration algorithm can be used in the present invention, for example, a binary tree search algorithm is preferred, referring to “Carrier leakage suppression in direct-conversion WCDMA transmitters” G. Brenna, D. Tschopp, and Q. Huang, IEEE ISSCC Dig. Tech. Papers, pp. 270-271, San Francisco, Calif., February 2003; and “A 2-Ghz carrier leakage calibrated direct-conversion WCDMA transmitter in 0.13-_m CMOS”, G. Brenna et al., IEEE J. Solid-State Circuit, vol. 39, pp. 1253-1262, August 2004.
The calibration detection/determination unit 81 provides a calibration compensation unit 83 with the compensation signal, and the compensation unit 83 feeds the compensation signal to summing devices 11 and 12, so that the compensation signal is incorporated into each of the input I and Q signals Ibb and Qbb by the summing devices 11, 12 in the transmission condition, so as to eliminate or reduce the leakage. Digital to analog conversion is done before the compensation signal is fed to the summing device 11 or 12.
The calibration detection/determination unit 81 and the calibration compensation unit 83 can be combined as a single calibration processing unit (not shown).
As mentioned above, the converting/steering device 40 has two modes including a normal mode and a calibration mode. In the normal mode, the converting/steering device 40 operates as a variable gain amplifier to adjust the output signal with a variable gain. In the calibration mode, the converting/steering device 40 operates as a down-mixer to down-convert the RF leakage signal to the lowered frequency.
FIG. 2 is a block diagram schematically showing the converting/steering device 40. As shown in this drawing, the converting/steering device 40 preferably comprises a steering and mixing module, which is implemented by a merged mixer/variable gain amplifier (VGA) 43. In addition, the device 40 also has a mode controller 45. The merged mixer/VGA 43 has a mixing stage 431 and an amplifying stage 433 (detailed later). The mode controller 45 receives a mode selection signal SEL and switches the merged mixer/VGA 43 to be in one of the normal mode and calibration mode.
In a preferred embodiment, when the DCT is under the transmission condition, the mode controller 45 controls DC biases of the merged mixer/VGA 43 to switch the merged mixer/VGA 43 into the normal mode, and blocks the second local oscillator signal LO2 generated by the second local oscillator 50 from entering into the merged mixer/VGA 43, so that the amplifying stage 433 operates as an RF VGA, while the mixing stage 431 does not work.
When the DCT is under the calibration condition, the mode controller 45 controls DC biases of the merged mixer/VGA 43 to switch the merged mixer/VGA 43 into the calibration mode, and allows the second local oscillator (LO) signal LO2 generated by the second local oscillator 50 to enter into the merged mixer/VGA 43, so that the mixing stage 431 operates as a down-mixer, while the amplifying stage 433 can be disactivated or operate as an amplifier to amplify the down-converted leakage, so that it is easy to detect the amplified leakage. The details concerning this matter will be further described.
FIG. 3 illustrates a merged mixer/VGA 43 in accordance with an embodiment of the present invention. The merged mixer/VGA 43 of FIG. 3 includes the mixing stage 431 implemented by a double balanced switch quad having four transistors Q1, Q2, Q3 and Q4, which are connected to form a double balanced mixer, and the amplifying stage 433 implemented by a steering quad having four transistors Q5, Q6, Q7 and Q8, which are connected to form an RF VGA.
The bases of transistors Q1, Q2, Q3 and Q4 are LO/DC inputs. In the calibration mode, differential local oscillator components LOP and LON of the local oscillator signal LO2, as well as differential components of a DC bias signal are fed into the mixing stage 431 via the LO/DC inputs, that is, the bases of transistors Q1, Q2, Q3 and Q4 as shown.
In the normal (transmission) mode, the DC bias signal is controlled to turn off the transistors Q1, Q2, Q3 and Q4. Accordingly, the mixing stage 431 does not operate. In addition, no LO signal components are fed to the bases of transistors Q1, Q2, Q3 and Q4.
The bases of transistors Q5 and Q8 are connected together at a node N1, and the bases of transistors Q6 and Q7 are connected together at a node N2. Control signals VCP and VCN are applied to the amplifying stage 433 from the nodes N1 and N2, respectively. The operation and gain of the amplifying stage 433 can be controlled by adjusting the control signals VCP and VCN.
The emitters of transistors Q1, Q2, Q5 and Q6 are connected together as an input port, while the emitters of transistors Q3, Q4, Q7 and Q8 are connected together as another input port. The pair of input ports are connected to an input stage 435, which is known in this field, and the description thereof is omitted herein.
In the normal mode, a signal to be processed is input into the merged mixer/VGA 43 from the input ports, and is steered with a predetermined gain by the amplifying stage 433. In the calibration mode, a leakage is input into the merged mixer/VGA device 43 from the input ports, and is down-converted by the mixing stage 431 with the local oscillator components LOP and LON of the second LO signal LO2.
The collectors of transistors Q1, Q3 and Q8 are connected together as an output port, and the collectors of transistors Q2, Q4 and Q5 are connected together as another output port. The gain-steered or down-converted signal is output from the pair of output ports. The output ports are connected to a load stage 437, which is formed by shunted resistors, for instance. The collectors of transistors Q6 and Q7 are connected to a power source VCC.
As mentioned above and shown in the FIG. 3, the amplifying stage 433 have the four transistors Q5, Q6, Q7 and Q8 connected as an RF VGA. The amplifying stage 433 including these four transistors Q5, Q6, Q7 and Q8 is referred to a single stage RF VGA circuit.
In another embodiment, an RF VGA circuit with two or more stages can be used. One stage of the RF VGA circuits is merged with the mixing stage 431 as illustrated in FIG. 3, while the other stage(s) is/are connected with the merged stage in a cascade form. It is noted that only the merged stage RF VGA is used as the amplifying stage 433 in accordance with the present invention, while the other stage(s) is/are used as normal RF VGA(s).
The controls of DC bias, LO and control signals are performed by the mode controller 45. The mode controller 45 receives a mode selection signal SEL indicating the operation condition of the direct conversion transmitter and selects either the normal (transmission) mode or calibration mode accordingly.
The mode controller 45 includes a DC control unit 451 and a LO control unit 453.
The DC bias signal for the mixing stage 431 and the control signals VCP, VCN for the amplifying stage 433 are controlled by DC control unit 451 of the mode controller 45.
In the normal mode, the control signals VCP and VCN for the amplifying stage 433 are applied via a normal path other than the mode controller 45. The DC bias signals of the mixing stage 431 are controlled so that the current is forced to flow through the amplifying stage 433 rather than the mixing stage 431. For example, the DC control unit 451 may pull-down the level of the DC bias signal of the mixing stage 431 to zero so that transistors Q1, Q2, Q3 and Q4 are turned off. Alternatively, the level of DC bias of the mixing stage 431 can be dropped lower than the control signals VCP, VCN, whereby the current is forced to flow through the amplifying stage 433. In addition, the LO control unit 453 blocks the second LO signal LO2 generated by the second local oscillator 50, so that no LO signal enters into the mixing stage 431.
In the calibration mode, the DC control unit 451 of the mode controller 45 controls the level of the DC bias for the mixing stage 431 to be higher than the control signals VCP, VCN, so that the current is forced to flow through the mixing stage 431. It is preferred that the control signals VCP, VCN are also controlled by the mode controller 45 in the calibration mode to ensure that a great portion or all of the current flow through the mixing stage 431. In this manner, the down-conversion function can be performed smoothly. Furthermore, the LO control unit 453, which receives the second LO signal LO2 from the second local oscillator 50, passes the second LO signal LO2 to the mixing stage 431, that is, the bases of transistors Q1, Q2, Q3 and Q4 in the calibration mode. Accordingly, the mixing stage 431 can mix the input signal fed through the input ports with the LON, LOP, the differential components of the second LO signal LO2, to generate a down-converted output signal.
FIG. 5 illustrates a merged mixer/VGA 43′ in accordance with another embodiment of the present invention. The structure of the merged mixer/VGA 43′ is similar to that of the merged mixer VGA 43 in FIG. 3. A mixing stage of the merged mixer/VGA 43′ comprises transistors Q1, Q2, Q3 and Q4 constituting a double balanced switch quad; and an amplifying stage thereof comprises transistors Q5, Q6, Q7 and Q8 constituting a steering quad. The pair of input ports of the merged mixer/VGA 43′ are connected to an input stage 535. The pair of input ports of the merged mixer/VGA 43′ are respective the connection of the emitters of transistors Q1, Q2, Q5 and Q6 and the connection of the emitters of transistors Q3, Q4, Q7 and Q8. As described, the mixer/VGA 43 in FIG. 3 has only one pair of output ports (the collectors of transistors Q1, Q3 Q8 and the collectors of transistors Q2, Q4, Q5) and the one pair of output ports are connected to the load stage 437. Different from the mixer/VGA 43, the mixer/VGA 43′ has two pairs of output ports. A first pair of output ports Out1_p and Out1_n are respectively the collectors of transistors Q5 and Q8. A second pair of output ports Out2_p and Out2_n are respectively the collectors connection of transistors Q2, Q4 and the collector connection of transistors Q1, Q3. In addition, the first pair of output ports are connected to a first load stage (Load 1) 537, while the second pair of output ports are connected to a second load stage (Load 2) 539.
In the embodiments of the present invention, the transistors Q1 to Q8 are implemented by bipolar junction transistors (BJTs). However, other types of transistors, such as CMOS, also can be used.
While the preferred embodiment of the present invention has been illustrated and described in detail, various modifications and alterations can be made by persons skilled in this art. The embodiment of the present invention is therefore described in an illustrative but not restrictive sense. It is intended that the present invention should not be limited to the particular forms as illustrated, and that all modifications and alterations which maintain the spirit and realm of the present invention are within the scope as defined in the appended claims.

## Claims

1. A merged converting/steering device having a first mode for operating as a variable gain amplifier, and a second mode for operating as a mixer, said device comprising:
a load stage for providing a load;
a mixing stage having a LO/DC input pair for inputting a local oscillator signal and a DC bias signal, a first signal input pair for inputting an input signal, and a first signal output pair connected to said load stage, said mixing stage modulating the input signal with said local oscillator signal when activated; and
an amplifying stage having a control input pair for inputting control signals, a second signal input pair connected with said first signal input pair to be as a single signal input pair, a power supply input connected to a power source, and a second signal output pair connected with said first signal output pair to be as a single signal output pair, said amplifying stage steering the input signal with a gain depending on said control signals when activated,
wherein by controlling said DC bias signal and said control signals, the mixing stage is disactivated and the amplifying stage is activated for the first mode, and the mixing stage is activated for the second mode.

2. The device as claimed in claim 1, wherein the amplifying stage is disactivated for the second mode.

3. The device as claimed in claim 1, wherein said local oscillator signal is controlled to be fed to the LO/DC input pair in the second mode, while blocked in the first mode.

4. The device as claimed in claim 1, wherein said mixing stage is formed as a double balanced mixer.

5. The device as claimed in claim 4, wherein said mixing stage comprises a first transistor, a second transistor, a third transistor and a fourth transistor, the first transistor and the fourth transistor have first terminals thereof serve as one input port of said LO/DC input pair, the second transistor and the third transistor have first terminals thereof serve as the other input port of said LO/DC input pair, the first transistor and the second transistor have second terminals thereof connected together as one input port of said first input pair, the third transistor and the fourth transistor have second terminals thereof connected together as the other input port of the first input pair, the first transistor and the third transistor have third terminals connected together as one output port of said first output pair, and the second transistor and the fourth transistor have third terminals thereof connected together as the other output port of said first output pair.

6. The device as claimed in claim 5, wherein said transistors are bipolar junction transistors (BJTs), and the first terminals are base terminals, the second terminals are emitter terminals, and the third terminals are collector terminals.

7. The device as claimed in claim 1, wherein said amplifying stage is formed as a variable gain amplifier (VGA).

8. The device as claimed in claim 7, wherein said amplifying stage comprises a fifth transistor, a sixth transistor, a seventh transistor and an eighth transistor, the fifth transistor and the eighth transistor have first terminals thereof connected together as one input port of said control input pair, the sixth transistor and the seventh transistor have first terminals thereof connected together as the other input port of said control input pair, the fifth transistor and the sixth transistor have second terminals thereof connected together as one input port of said second input pair, the seventh transistor and the eighth transistor have second terminals thereof connected together as the other one input port of said second input pair, the fifth transistor and the eighth transistor have third terminals thereof serve as respective ports of said second output pair, and the sixth transistor and the seventh transistor have third terminals thereof serve as the power supply input.

9. The device as claimed in claim 8, wherein said transistors are bipolar junction transistors (BJTs), and the first terminals are base terminals, the second terminals are emitter terminals, and the third terminals are collector terminals.

10. The device as claimed in claim 1, wherein said mixing stage comprises a first transistor, a second transistor, a third transistor and a fourth transistor, said amplifying stage comprises a fifth transistor, a sixth transistor, a seventh transistor and an eighth transistor, the first transistor and the fourth transistor have first terminals thereof serve as one input port of said LO/DC input pair, the second transistor and the third transistor have first terminals thereof serve as the other input port of said LO/DC input pair, the fifth transistor and the eighth transistor have first terminals thereof connected together as one input port of said control input pair, the sixth transistor and the seventh transistor have first terminals thereof connected together as the other input port of said control input pair, the first transistor, second transistor, fifth transistor and sixth transistor have second terminals thereof connected together as one port of the single signal input pair, the third transistor, fourth transistor, seventh transistor and eighth transistor have second terminals thereof connected together as the other port of the single signal input pair, the second transistor, fourth transistor, and fifth transistor have third terminals thereof connected together as one port of the single signal output pair, the first transistor, third transistor and eighth transistor have third terminals thereof connected together as the other port of the single signal output pair, and the sixth transistor and seventh transistor have third terminals thereof serve as the power supply input.

11. The device as claimed in claim 10, wherein said transistors are bipolar junction transistors (BJTs), and the first terminals are base terminals, the second terminals are emitter terminals, and the third terminals are collector terminals.

12. The device as claimed in claim 1, further comprising a mode controller for controlling said DC bias signal and said control signals to switch the device to be in one of the first mode and second mode.

13. The device as claimed in claim 12, wherein the mode controller feeds the local oscillator signal to the LO/DC input pair in the second mode, while blocks the local oscillator signal in the first mode.

14. A direct conversion transmitter comprising:
an up-converter for mixing an in-phase (I) baseband signal and a quadrature-phase (Q) baseband signal with an RF carrier signal to generate an RF I and Q signals;
a summing device for combining said RF I and Q signals to be a combined RF signal;
a converting/steering device having a first mode and a second mode, said converting/steering device receiving said combined RF signal to adjust said combined RF signal with a gain in the first mode, while to down-convert an RF leakage signal into a lowered-frequency signal in the second mode; and
a calibration processing unit detecting said lowered-frequency signal from said converting/steering device, generating a compensation signal based on the detected lowered-frequency signal and providing said compensation signal to adjust said I baseband signal and Q baseband signal.

15. The direct conversion transmitter as claimed in claim 14, wherein said converting/steering device comprises:
a mixing stage having a LO/DC input pair for inputting a local oscillator signal and a DC bias signal, a first signal input pair for inputting an input signal, and a first signal output pair connected to a load stage, said mixing stage modulating the input signal with said local oscillator signal when activated; and
an amplifying stage having a control input pair for input control signals, a second signal input pair connected with said first signal input pair as a single signal input pair,
a power supply input connected to a power source, and a second signal output pair connected with said first signal output pair as a single signal output pair, said amplifying stage steering the input signal with a gain depending on said control signals when activated,
wherein said DC bias signal and said control signals are controlled so that the mixing stage is disactivated while the amplifying stage is activated in the first mode and the mixing stage is activated in the second mode.

16. The device as claimed in claim 15, wherein the amplifying stage is disactivated in the second mode.

17. The direct conversion transmitter as claimed in claim 15, wherein said local oscillator signal is controlled to be fed to the LO/DC input pair in the second mode, while blocked in the first mode.

18. The direct conversion transmitter as claimed in claim 15, wherein said mixing stage is formed as a double balanced mixer.

19. The direct conversion transmitter as claimed in claim 15, wherein said mixing stage comprises a first transistor, a second transistor, a third transistor and a fourth transistor, the first transistor and the fourth transistor have first terminals thereof serve as one input port of said LO/DC input pair, the second transistor and the third transistor have first terminals thereof serve as the other one input port of said LO/DC input pair, the first transistor and the second transistor have second terminal thereof connected together as one input port of said first input pair, the third transistor and the fourth transistor have second terminals thereof connected together as the other input port of the first input pair, the first transistor and the third transistor have third terminals connected together as one output port of said first output pair, and the second transistor and the fourth transistor have third terminals thereof connected together as the other one output port of said first output pair.

20. The direct conversion transmitter as claimed in claim 19, wherein said transistors are bipolar junction transistors (BJTs), and the first terminals are base terminals, the second terminals are emitter terminals, and the third terminals are collector terminals.

21. The direct conversion transmitter as claimed in claim 15, wherein said amplifying stage is formed as a variable gain amplifier (VGA).

22. The direct conversion transmitter as claimed in claim 15, wherein said amplifying stage comprises a fifth transistor, a sixth transistor, a seventh transistor and an eighth transistor, the fifth transistor and the eighth transistor have first terminals thereof connected together as one input port of said control input pair, the sixth transistor and the seventh transistor have first terminals thereof connected together as the other one input port of said control input pair, the fifth transistor and the sixth transistor have second terminals thereof connected together as one input port of said second input pair, the seventh transistor and the eighth transistor have second terminals thereof connected together as the other input port of said second input pair, the fifth transistor and the eighth transistor have third terminals thereof serve as respective ports of said second output pair, and the sixth transistor and the seventh transistor have third terminals thereof serve as the power supply input.

23. The direct conversion transmitter as claimed in claim 22, wherein said transistors are bipolar junction transistors (BJTs), and the first terminals are base terminals, the second terminals are emitter terminals, and the third terminals are collector terminals.

24. The direct conversion transmitter as claimed in claim 15, wherein said mixing stage comprises a first transistor, a second transistor, a third transistor and a fourth transistor, said amplifying stage comprises a fifth transistor, a sixth transistor, a seventh transistor and an eighth transistor, the first transistor and the fourth transistor have first terminals thereof together serve as one input port of said LO/DC input pair, the second transistor and the third transistor have first terminals thereof together serve as the other one input port of said LO/DC input pair, the fifth transistor and the eighth transistor have first terminals thereof connected together as one input port of said control input pair, the sixth transistor and the seventh transistor have first terminals thereof connected together as the other input port of said control input pair, the first transistor, second transistor, fifth transistor and sixth transistor have second terminals thereof connected together as one port of the single signal input pair, the third transistor, fourth transistor, seventh transistor and eighth transistor have second terminals thereof connected together as the other one port of the single signal input pair, the second transistor, fourth transistor, and fifth transistor have third terminals thereof connected together as one port of the single signal output pair, the first transistor, third transistor and eighth transistor have third terminals thereof connected together as the other one port of the single signal output pair, and the sixth transistor and seventh transistor have third terminals thereof serve as the power supply input.

25. The direct conversion transmitter as claimed in claim 24, wherein said transistors are bipolar junction transistors (BJTs), and the first terminals are base terminals, the second terminals are emitter terminals, and the third terminals are collector terminals.

26. The direct conversion transmitter as claimed in claim 15, wherein said converting/steering device further comprises a mode controller for controlling said DC bias signal and said control signals to switch the device to be in one of the first mode and second mode.

27. The direct conversion transmitter as claimed in claim 26, wherein the mode controller feeds the local oscillator signal to the LO/DC input pair in the second mode, while blocks the local oscillator signal in the first mode.

28. A steering and mixing module, comprising:
a double balanced switch quad; and
a steering quad;
wherein during a normal mode the steering quad is activated, and during a calibration mode the double balanced switch quad is activated.