Return-type current-reuse mixer

This application is the U.S. national phase of PCT Application No. PCT/CN2011/078565 filed on Aug. 18, 2011, which claims priority to Chinese Patent Application No. 201110004140.2 filed on Jan. 11, 2011, the disclosures of which are incorporated in their entirety by reference herein.

The present invention relates to a return-type current reuse frequency mixer, which contains a transconductance/amplifier stage and a mixer stage. Radio frequency signal is down converted into intermediate frequency signal via transconductance stage and mixer stage, and then is fed back to the transconductance stage for intermediate frequency amplification; the amplified signal is output after being filtered by a first-order low-pass filter. The transconductance stage of the frequency mixer amplifies both the input radio frequency signal and output intermediate frequency signal; to ensure circuit stability, the radio frequency signal/intermediate frequency signal are coupled and isolated by means of low-pass/high-pass filter networks. The structure has advantages of reduced power consumption, simplified circuit structure and high conversion gain, and is applicable to low-power and low-cost constant-envelope communication standard.

Return-type circuit is based on regenerative circuit. Regenerative circuit technology emerged in early-stage vacuum tube receivers first. Owing to the high price of vacuum tubes at that time, receiver designers began to seek paths for building the entire receiver with least number of vacuum tubes. An American Edwin Armstrong invented regenerative circuit, which made the implementation of single tube receiver possible. The working principle of regenerative circuit is: under the amplification and nonlinear actions of vacuum tube, an signal that contains amplified radio frequency signal and demodulated audio signal is output by radio frequency broadcast signal, and a part of the output signal is fed back to the input terminal of the vacuum tube again for amplification by means of positive feedback technology; in that way, oscillation of input signal occurs at the input terminal of the vacuum tube, and thereby the input radio frequency signal is “regenerated”. Since the oscillation tends to saturate, the ultimate amplitude of oscillation is fixed and the amplitude of output demodulated audio signal is also fixed for input signals with different intensities; the receiving volume is almost the same for radio stations with different intensities; therefore, the volume control process can be omitted. It is noted that the oscillation process should surely not be endless. In the circuit, the oscillation signal can be “reset” automatically at a short interval, so that oscillation is restarted and maintained according to the input signal, in order to track and regenerate the input signal at any time. In summary, regenerative circuit allows for operating in an intermittent non-steady state. In many cases, the function of receiver can be implemented with a single tube. Regenerative circuit breaks the provisions of gain-bandwidth product being constant in a first-order approximation system, and increases the equivalent Q value of the receiving circuit. The intermediate frequency amplification tube can be omitted, and the cost of receiver can be reduced; in addition, the power consumption is reduced, though reduction of power consumption was not a concern at that time. However, regenerative circuit in its early stage also faced some problems, for example, the circuit will amplify the noise infinitely when there is no signal input, causing hissing noise from the speaker; the emitted oscillating signal will interfere with other receivers; some circuit knowledge is required to accomplish adjustment of regenerative circuit, and the frequency selectivity is poor, etc. Regenerative circuit emerged in the times when all possible efforts were made to save tubes. Though the performance of regenerative circuit is barely satisfactory, the design concept of regenerative circuit has brought a unique idea to the circuit designers.

The positive feedback of regenerative circuit was the main cause for the drawbacks, but the full utilization of amplifier tube brought inspirations to the designers later. In the following several years, the prototype of return-type structure was put forth, i.e., the input high-frequency signal and the output demodulated intermediate frequency signal share the same amplifier stage. To prevent the occurrence of positive feedback, the radio frequency signal and intermediate frequency signal were isolated by means of high-pass and low-pass filter networks at the same time. However, the maximum frequency of short-wave audio broadcast at that time was only several MHz to tens of MHz, which differed only by 2 to 3 orders from the output audio. Therefore, the effect of isolation between radio frequency signal and output intermediate frequency signal was poor, and the receiving quality was poor due to mutual interference. With the emergence and development of transistor technology, the cost of tube was greatly reduced, and receivers with superheterodyne structure began to popularize; in comparison, the cost advantage of regenerative structure and return-type structure no longer existed. Therefore, regenerative structure and return-type structure were forgotten for a long time.

At present, radio frequency communication circuits usually have carrier frequency as high as 2-5 GHz and output intermediate frequency within a range of 2-10 MHz. The radio frequency signal and intermediate frequency signal can be isolated effectively by means of a simple first-order passive filter network. As portable communication means and wireless sensing networks are widely applied, how to reduce power consumption and increase battery life has become a purpose of the designers. The concept of radio frequency/intermediate frequency gain reuse of return-type circuit provides an approach for reduction of power consumption. In the present invention, the concepts related with the forgotten regenerative return-type circuit are merged into the design of integrated circuits, and thereby a novel low-power return-type frequency mixer is built.

Technical Problem

The object of the present invention is to provide a low-power return-type frequency mixer, in which the transconductance stage employs current reuse technology, and the input radio frequency signal and output intermediate frequency signal share the same transconductance/amplifier stage, and therefore the low-power return-type frequency mixer has advantages of reduced power consumption, simplified circuit structure, and high conversion gain.

Technical Solution

The object of the present invention is attained by the following technical scheme: as shown in FIG. 1 a , a conventional frequency mixer mainly comprises three modules connected in sequence, i.e., a transconductance stage, a mixer stage, and a low-pass filter stage. A radio frequency signal is converted into radio frequency current by means of the transconductance stage, the current generates down-converted signal which is located at intermediate frequency, input feed-through signal which is located at radio frequency and up-converted signal at the output terminal under the modulation action of the mixer stage. After above signals have passed the low-pass filter network, the feed-through signal and up-converted signal are filtered off, and the pure down-converted signal is obtained at the output terminal.

A return-type current reuse frequency mixer, comprising a transconductance/amplifier stage and a mixer stage connected in sequence, wherein, the transconductance/amplifier stage amplifies input radio frequency signal, and the amplified radio frequency signal passes through the mixer stage and produces output intermediate frequency signal; the intermediate frequency signal is fed back to the input terminal of the transconductance/amplifier stage again, and then serves as the final intermediate frequency signal output after amplified by the transconductance/amplifier stage;

a high-pass filter network is serially connected between the transconductance/amplifier stage and the mixer stage, to block the intermediate frequency signal; a low-pass filter network is serially connected between the output terminal of the mixer stage and the transconductance/amplifier stage, to block the radio frequency signal;

the transconductance/amplifier stage employs a current reuse structure, and serves as a transconductance stage for the radio frequency signal and an amplifier stage for the intermediate frequency signal.

Specifically, the transconductance/amplifier stage comprises: PMOS transistors PM 0 and PM 3 ; NMOS transistors NM 0 and NM 1 ; capacitors C 0 and C 1 ; capacitors C 2 and C 3 ; and, resistors R 1 , R 2 , R 3 and R 4 ;

PM 0 , NM 0 , PM 3 and NM 1 constitute a current reuse transconductance stage; NM 0 and NM 1 serve as the amplifier tubes for the output intermediate frequency signal simultaneously, and the final output signals are output from the drain electrodes of NM 0 and NM 1 ;

the mixer stage comprises: double balanced switches PM 4 , PM 5 , PM 6 , and PM 7 ; PMOS transistors PM 1 and PM 2 that are used as bias transistors, wherein, PM 4 to PM 7 constitute the core mixer circuit, and current bias is provided by PM 1 and PM 2 ; and, NMOS transistors NM 2 and NM 3 that are used as mixing loads;

the DC bias voltage for the transconductance stage is provided by the gate voltage of NM 2 and NM 3 ; radio frequency coupling capacitors C 4 and C 5 are connected between the transconductance stage and mixer stage and serve as a high-pass filter network to couple the radio frequency signal and isolate the final intermediate frequency signal output;

the low-pass filter network comprises C 6 , R 5 , C 7 , C 9 , R 6 , C 8 and C 10 , to couple the intermediate frequency signal output from the mixer stage to the transconductance/amplifier stage and isolate the radio frequency signal output from the mixer stage;

the upper pole plates of capacitors C 0 and C 1 are connected to the positive input signal terminal, and the lower pole plate of C 1 is connected to the gate electrode of PM 0 ; the lower pole plate of C 0 is connected to the gate electrode of NM 0 ; the upper pole plates of capacitors C 2 and C 3 are connected to the positive input signal terminal, and the lower pole plate of C 3 is connected to the gate electrode of PM 3 ; the lower pole plate of C 2 is connected to the gate electrode of NM 1 ;

the source electrode of PM 0 is connected to the supply voltage, and the drain electrode of PM 0 is connected to the drain electrode of NM 0 ; the positive terminal of resistor R 1 is connected to the gate electrode of PM 0 , the negative terminal of resistor R 1 is connected to the positive terminal of resistor R 2 , and the negative terminal of R 2 is connected to the drain electrode of PM 0 ; the source electrode of PM 3 is connected to the supply voltage, and the drain electrode of PM 3 is connected to the drain electrode of NM 1 ; the positive terminal of resistor R 3 is connected to the gate electrode of PM 3 , the negative terminal of resistor R 3 is connected to the positive terminal of R 4 , and the negative terminal of R 4 is connected to the drain electrode of PM 3 ; the negative terminal of R 1 and the negative terminal of R 3 are connected to the upper pole plate of capacitor C 12 at the same time, and the lower pole plate of C 12 is grounded;

the drain electrodes of NM 0 and NM 1 are grounded; the source electrodes of PM 1 and PM 2 are connected to the supply voltage, and the gate electrodes of PM 1 and PM 2 are connected to the gate voltage of a current mirror; the source electrodes of PM 4 and PM 5 are connected to the drain electrode of PM 1 , and the source electrodes of PM 6 and PM 7 are connected to the drain electrode of PM 2 ; the positive terminal of local oscillator signal is connected to the gate electrodes of PM 5 and PM 6 , and the negative terminal of local oscillator signal is connected to the gate electrodes of PM 4 and PM 7 ;

the source electrodes of NM 2 and NM 3 are grounded, the gate electrodes of NM 2 and NM 3 are connected to the upper pole plate of capacitor C 11 , and the lower pole plate of capacitor C 11 is grounded; the drain electrode of NM 2 is connected to the drain electrodes of PM 4 and PM 6 ; the drain electrode of NM 3 is connected to the drain electrodes of PM 5 and PM 6 ;

the upper pole plate of capacitor C 4 is connected to the drain electrode of PM 0 , and the lower pole plate of capacitor C 4 is connected to the drain electrode of PM 1 ; the upper pole plate of capacitor C 5 is connected to the drain electrode of PM 3 , and the lower pole plate of capacitor C 5 is connected to the drain electrode of PM 2 ; the positive terminal of resistor R 7 is connected to the drain electrode of NM 2 , and the negative terminal of resistor R 7 is connected to the gate electrode of NM 2 ; the positive terminal of R 8 is connected to the drain electrode of NM 3 , and the negative terminal of R 8 is connected to the gate electrode of NM 3 ; the capacitor C 6 is bridge-connected between the positive terminal of R 7 and the positive terminal of R 8 ; the upper pole plate of capacitor C 9 is connected to the drain electrode of NM 2 , and the lower pole plate of C 9 is grounded; the upper pole plate of capacitor C 10 is connected to the drain electrode of NM 3 , and the lower pole plate of C 10 is grounded; the positive terminal of resistor R 5 is connected to the drain electrode of NM 2 , the negative terminal of R 5 is connected to the gate electrode of NM 0 and the upper pole plate of capacitor C 7 , and the lower pole plate of C 7 is grounded; the positive terminal of resistor R 6 is connected to the drain electrode of NM 3 , the negative terminal of R 6 is connected to the gate electrode of NM 1 and the upper pole plate of capacitor C 8 , and the lower pole plate of C 8 is grounded;

the positive terminal of R 9 is connected to an output node 1 , the negative terminal of R 9 is the positive terminal of intermediate frequency signal output and is connected to the upper pole plate of the capacitor C 13 , and the lower pole plate of C 13 is grounded; the positive terminal of R 10 is connected to an output node 2 , the negative terminal of R 10 is the negative terminal of intermediate frequency signal output and is connected to the upper pole plate of capacitor C 14 , and the lower pole plate of C 14 is grounded; the output node 1 is placed at the negative terminal of resistor R 2 , and the output node 2 is placed at the negative terminal of resistor R 4 .

The working principle of the technical scheme is as follows:

As shown in FIG. 1 b , in the return-type frequency mixer of the present invention, a high-pass filter network is serially connected between the transconductance stage and the mixer stage, and the output of the mixer stage is connected to a low-pass filter network and then coupled to the transconductance/amplifier stage. The signal is amplified by means of the transconductance/amplifier stage and then output. For the input radio frequency signal, the transconductance/amplifier stage is a current reuse transconductance stage; for the output intermediate frequency signal, the transconductance/amplifier stage serves as an intermediate frequency amplifier. Viewed from the physical structure, the output of the mixer stage is connected to the input of the transconductance/amplifier stage, to form a loop. However, owing to the intervention of the high-pass/low-pass filter networks, the radio frequency signal is blocked at the output terminal of the mixer stage, and the intermediate frequency signal is blocked at the output terminal of the transconductance stage. Actually, no feed-back loop is formed. Since there is a difference of thousands times between the radio frequency signal and the output intermediate frequency signal, a reliable isolation effect can be achieved by means of first-order passive high-pass/low-pass filter networks. FIG. 3 shows the loop gain of the physical loop in the entire frequency domain. It can be seen that the loop gain value at any frequency is lower than 0 dB, which is to say, no oscillation will be produced at any frequency in the frequency mixer.

The structure of the frequency mixer of the present invention is shown in FIG. 2 . The frequency mixer employs an input/output full-differential structure. The differential terminals of the transconductance stage are consisted of PM 0 , NM 0 , and PM 3 , NM 1 . The input radio frequency signal is coupled to the gate electrode of the PMOS transistor and the gate electrode of the NMOS transistor via capacitors at the same time. The radio frequency current generated by the transconductance stage is coupled to the local oscillator stage via small capacitors C 4 and C 5 . The capacitors allow for complete feeding-through of the radio frequency signal, but are similar to an open circuit for the intermediate frequency signal, which is to say, the intermediate frequency signal is blocked before the mixer stage. The mixing stage and transconductance stage are biased separately, so that lower bias current can be used for the mixer stage and thereby the noise factor of the frequency mixer can be improved. The converted signals are output from the drain electrodes of NM 2 and NM 3 , filtered in the first-order low-pass filters to filter off radio frequency signal, and then applied to the gate electrodes of NM 0 and NM 1 . The final intermediate frequency output is generated in the drain electrodes of NM 0 and NM 1 . FIG. 4 shows the curve of conversion gain of the output terminal of the mixer stage (lower curve) and the curve of conversion gain of the output terminal of the trans conductance/amplifier stage (upper curve) with input frequency, wherein, the local oscillator frequency is 2.45 GHz; as can be seen clearly from the figure, due to the introduction of return-type structure, the conversion gain is increased by more than 20 dB with the same power consumption and active components.

Beneficial Effects

The frequency mixer comprises a transconductance/amplifier stage, a mixer stage, and high-pass and low-pass filter networks; the transconductance/amplifier stage employs a current reuse CMOS structure, wherein an input radio frequency signal is converted into radio frequency current; the current is filtered through the high-pass filter network to filter off the low frequency component and then fed into the mixer stage; in the mixer stage, intermediate frequency signal is generated and output under the modulation action of the mixer stage. The intermediate frequency signal is filtered through a low-pass filter network to filter off the high frequency component and then is sent again for input into the transconductance/amplifier stage, amplified by the transconductance/amplifier stage, and then output; the transconductance stage of the frequency mixer employs current reuse technology, and the input radio frequency signal and output intermediate frequency signal share the same transconductance/amplifier stage. Therefore, the frequency mixer of the present invention has advantages of reduced power consumption, simplified circuit structure, and high conversion gain.

FIG. 1 a is a modular block diagram of a conventional frequency mixer;

FIG. 1 b is a modular block diagram of the return-type current reuse frequency mixer of the present invention;

FIG. 2 is a schematic circuit diagram of the return-type current reuse frequency mixer of the present invention;

FIG. 3 shows an internal loop gain curve of the return-type current reuse frequency mixer of the present invention in the entire spectral range;

FIG. 4 shows a curve of conversion gain of the output terminal of the mixer stage (lower curve) and a curve of conversion gain of the output terminal of the transconductance/amplifier stage (upper curve) with input frequency, wherein, the local oscillator frequency is 2.45 GHz;

FIG. 5 shows a waveform of input radio frequency signal (curve in light color), a waveform of the output terminal of the mixer stage (low frequency sinusoidal wave with lower amplitude), and a waveform of intermediate frequency signal of the output terminal of the transconductance/amplifier stage (low frequency sinusoidal wave with higher amplitude).

The main structure of the return-type current reuse frequency mixer of the present invention mainly comprises a transconductance/amplifier stage, a mixer stage, biasing circuits, and filter networks, etc. The transconductance/amplifier stage comprises P-channel metal oxide field effect transistors (hereinafter called as PMOS transistors) PM 0 and PM 3 , and N-channel metal oxide field effect transistors (hereinafter called as NMOS transistors) NM 0 and NM 1 . PM 0 , NM 0 , and PM 3 and NM 1 constitute a current reuse transconductance stage. NM 0 and NM 1 serve as amplifier transistors for the output intermediate frequency signal, and the final output signals are output from the drain electrodes of NM 0 and NM 1 . Double balanced switches PM 4 -PM 7 serve as the core circuit of frequency mixer, and the current bias is provided by bias transistors PM 1 and PM 2 . The DC bias voltage for the transconductance stage is provided by the gate voltage of mixing load transistors NM 2 and NM 3 . Capacitors C 4 and C 5 are placed between the transconductance stage and the mixer stage, to couple the radio frequency signal and isolate the intermediate frequency output signal. C 6 , R 5 , C 7 , C 9 and R 6 , C 8 , C 10 constitute a low-pass filter network, to couple the intermediate frequency signal output from the mixer stage to the transconductance/amplifier stage and isolate the radio frequency signal output from the mixer stage.

The upper pole plates of capacitors C 0 and C 1 are connected to the positive signal input terminal, and the lower pole plate of C 1 is connected to the gate electrode of PM 0 ; the lower pole plate of C 0 is connected to the gate electrode of NM 0 ; the upper pole plates of capacitors C 2 and C 3 are connected to the positive signal input terminal, and the lower pole plate of C 3 is connected to the gate electrode of PM 3 ; the lower pole plate of C 2 is connected to the gate electrode of NM 1 ; the source electrode of PM 0 is connected to the supply voltage, and the drain electrode of PM 0 is connected to the drain electrode of NM 0 ; the positive terminal of resistor R 1 is connected to the gate electrode of PM 0 , the negative terminal of R 1 is connected to the positive terminal of resistor R 2 , and the negative terminal of R 2 is connected to the drain electrode of PM 0 . The source electrode of PM 3 is connected to the supply voltage, and the drain electrode of PM 3 is connected to the drain electrode of NM 1 . The positive terminal of resistor R 3 is connected to the gate electrode of PM 3 , the negative terminal of R 3 is connected to the positive terminal of R 4 , and the negative terminal of R 4 is connected to the drain electrode of PM 3 . The negative terminal of R 1 and the negative terminal of R 3 are connected to the upper pole plate of capacitor C 12 simultaneously, and the lower pole plate of C 12 is grounded. The drain electrodes of NM 0 and NM 1 are grounded. The source electrodes of PM 1 and PM 2 are connected to the supply voltage, and the gate electrodes of PM 1 and MP 2 are connected to the gate voltage of a current mirror. The source electrodes of PM 4 and PM 5 are connected to the drain electrode of PM 1 , and the source electrodes of PM 6 and PM 7 are connected to the drain electrode of PM 2 ; the positive terminal of local oscillator signal is connected to the gate electrodes of PM 5 and PM 6 , and the negative terminal of local oscillator signal is connected to the gate electrodes of PM 4 and PM 7 . The source electrodes of NM 2 and NM 3 are grounded, the gate electrodes of NM 2 and NM 3 are connected to the upper pole plate of capacitor C 11 , and the lower pole plate of capacitor C 11 is grounded. The drain electrode of NM 2 is connected to the drain electrodes of PM 4 and PM 6 ; the drain electrode of NM 3 is connected to the drain electrodes of PM 5 and PM 6 . The upper pole plate of radio frequency coupling capacitor C 4 is connected to the drain electrode of PM 0 , and the lower pole plate of C 4 is connected to the drain electrode of PM 1 ; the upper pole plate of radio frequency coupling capacitor C 5 is connected to the drain electrode of PM 3 , and the lower pole plate of C 5 is connected to the drain electrode of PM 2 ; the positive terminal of resistor R 7 is connected to the drain electrode of NM 2 , and the negative terminal of R 7 is connected to the gate electrode of NM 2 . The positive terminal of R 8 is connected to the drain electrode of NM 3 , and the negative terminal of R 8 is connected to the gate electrode of NM 3 . The capacitor C 6 is bridge-connected between the positive terminal of R 7 and the positive terminal of R 8 . The upper pole plate of capacitor C 9 is connected to the drain electrode of NM 2 , and the lower pole plate of C 9 is grounded. The upper pole plate of capacitor C 10 is connected to the drain electrode of NM 3 , and the lower pole plate of C 10 is grounded. The positive terminal of resistor R 5 is connected to the drain electrode of NM 2 , the negative terminal of R 5 is connected to the gate electrode of NM 0 and the upper pole plate of capacitor C 7 , and the lower pole plate of C 7 is grounded. The positive terminal of resistor R 6 is connected to the drain electrode of NM 3 , the negative terminal of R 6 is connected to the gate electrode of NM 1 and the upper pole plate of capacitor C 8 , and the lower pole plate of C 8 is grounded. The positive terminal of R 9 is connected to an output node 1 , the negative terminal of R 9 serves as the positive terminal for intermediate frequency signal output and is connected to the upper pole plate of capacitor C 13 , and the lower pole plate of C 13 is grounded. The positive terminal of R 10 is connected to an output node 2 , the negative terminal of R 10 serves as the negative terminal for intermediate frequency signal output and is connected to the upper pole plate of capacitor C 14 , and the lower pole plate of C 14 is grounded.

The above content is only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. Those having ordinary skills in the art should recognize that various variations and modifications can be made according to the disclosure of the present invention without departing from the spirit and scope of the present invention as defined by the accompanying claims.