Utility model content
The purpose of this utility model is to provide a kind of S-band high linearity that can overcome above-mentioned technical problem, the down-conversion active mixer of low noise and low gain, the utility model is applied in down-conversion receiver, the utility model can improve the linearity and the noiseproof feature of frequency mixer under low gain condition, the structure that the utility model adopts is based on gilbert (Gilbert) type unit, the utility model adopts linearization technique and noise reduction technology to improve active mixer performance, the utility model have also been devised local oscillator drive circuit to provide a good local oscillator input signals and to improve overall circuit performance.The utility model is made up of transconductance stage circuit, switching stage circuit, load stage circuit, local oscillator drive circuit; Described local oscillator drive circuit is connected with switching stage circuit, and described load stage circuit, switching stage circuit, transconductance stage circuit connect successively.
The utility model adopts gilbert (Gilbert) type circuit topological structure, and transconductance stage circuit of the present utility model is made up of two transistors, for completing the transformation of radio frequency voltage signal to current signal.A transconductance stage input circuit analysis mode simplified is as shown in formula (1):
Described IIP3 is a parameter of tolerance mixer linearity degree, in formula (1), and α
1and α
3represent single order and the third order intermodulation factor respectively, I
dfrequency mixer transconductance stage electric current, K
rFit is transconductance stage transistor parameter.Can find out that frequency mixer transconductance stage electric current is larger by formula (1), the linearity is better, little transconductance stage transistor size also can make mixer linearity degree improve, but undersized transconductance stage transistor also can cause the increase of noise contribution, the utility model has taken into full account trading off between noise and the linearity at this.
Switching stage circuit of the present utility model is made up of four identical bipolar transistors and two Injection Current sources, for completing mixing and the pulse current injectingt function of radiofrequency signal and local oscillation signal, because bipolar transistor has lower flicker noise relative to MOS transistor, and bipolar transistor is much smaller for the requirement of local oscillation signal amplitude, so the utility model adopts bipolar transistor as switching tube, and owing to obtaining a good switch performance and noise perfomiance requirements switching tube electric current can not be very large, the big current of this and transconductance stage requires not to be inconsistent, described switching stage circuit of the present utility model adopts current injection to solve above-mentioned contradiction.
Load stage circuit of the present utility model is made up of two RC circuit in parallel, for completing the function such as transformation and gain-adjusted of intermediate frequency output current signal to voltage signal, described RC circuit can use as a low pass filter and can regulate mixer gain and linearity performance.
Local oscillator drive circuit of the present utility model adopts two-stage structure for amplifying, and the first order amplifying circuit of local oscillator drive circuit of the present utility model is for realizing single-ended local oscillation signal to the conversion of both-end local oscillator differential signal and signal amplifying function; The second level amplifying circuit of local oscillator drive circuit of the present utility model carries out amplifying for difference local oscillation signal and processes the local oscillator input port of rear output difference local oscillation signal to active mixer.
The utility model has the advantages that the feature with low-power consumption, high linearity and low noise, the linearity and the noiseproof feature of frequency mixer can be improved under low gain condition.
Embodiment
In order to make the purpose of this utility model, technical scheme and advantage clearly, below in conjunction with accompanying drawing, the utility model is described in further detail, but protection range of the present utility model is not limited to following description.
Transconductance stage circuit of the present utility model as shown in Figure 1, is made up of two transistors, for completing the transformation of radio frequency voltage signal to current signal.A transconductance stage input circuit analysis mode simplified is as shown in formula (1):
Described IIP3 is a parameter of tolerance mixer linearity degree, in formula (1), and α
1and α
3represent single order and the third order intermodulation factor respectively, I
dfrequency mixer transconductance stage electric current, K
rFit is transconductance stage transistor parameter.Can find out that frequency mixer transconductance stage electric current is larger by formula (1), the linearity is better, little transconductance stage transistor size also can make mixer linearity degree improve, but undersized transconductance stage transistor also can cause the increase of noise contribution, the utility model has taken into full account trading off between noise and the linearity at this.
In Fig. 1, transistor M1 and M2 forms transconductance stage circuit, RF+ and RF-represents the radio-frequency input signals of difference respectively, V1 and V2 is the gate bias voltage of transistor M1 and M2.
Switching stage circuit of the present utility model is made up of four identical bipolar transistors and two Injection Current sources, for completing mixing and the pulse current injectingt function of radiofrequency signal and local oscillation signal, as shown in Figure 2; Because bipolar transistor has lower flicker noise relative to MOS transistor, and bipolar transistor is much smaller for the requirement of local oscillation signal amplitude, so the utility model adopts bipolar transistor as switching tube, and owing to obtaining a good switch performance and noise perfomiance requirements switching tube electric current can not be very large, the big current of this and transconductance stage requires not to be inconsistent, and described switching stage circuit of the present utility model adopts current injection to solve above-mentioned contradiction.In Fig. 2, bipolar transistor Q1-Q4 is the switch amplifier transistor of switching stage circuit, I1 and I2 is Injection Current source, LO+ and LO-represents the local oscillator input signals of difference respectively, IF+ and IF-represents the IF output signal of difference, V1 is the base bias voltage of bipolar transistor Q1 and Q4, and V2 is the base bias voltage of Q2 and Q3.
Load stage circuit of the present utility model is made up of two RC circuit in parallel, for completing the function such as transformation and gain-adjusted of intermediate frequency output current signal to voltage signal, as shown in Figure 3; Described RC circuit can use as a low pass filter and can regulate mixer gain and linearity performance; In Fig. 3, R1, R2 and C1, C2 are resistance and the electric capacity of two RC parallel circuitss respectively, and Vdd is supply voltage.
Fig. 4 is local oscillator driving circuit structure figure of the present utility model, and local oscillator drive circuit of the present utility model is two-stage amplifying circuit, for providing for active mixer the oscillating driving signal that a quality is higher.
Local oscillator drive circuit of the present utility model adopts two-stage structure for amplifying, and the first order amplifying circuit of local oscillator drive circuit of the present utility model is for realizing single-ended local oscillation signal to the conversion of both-end local oscillator differential signal and signal amplifying function; The second level amplifying circuit of local oscillator drive circuit of the present utility model carries out amplifying for difference local oscillation signal and processes the local oscillator input port of rear output difference local oscillation signal to active mixer.
In Fig. 4, resistance R1-R4 is load resistance, LOIN is local oscillator input signals, and bipolar transistor Q1, Q2 form first order amplifying circuit, and I1 is tail current source, R5 is Input matching resistance, electric capacity C and Q1, Q2 complete the conversion of single-ended local oscillator input signals to differential signal, and bipolar transistor Q3 and Q4 forms second level amplifying circuit, and I2 is tail current source, OUT+ and OUT-is difference local oscillator output signal, and Vdd is supply voltage.
Fig. 5 is integrated circuit structure chart of the present utility model; Wherein left-hand component is its biasing circuit, for frequency mixer provides stable DC point; Mid portion is the core circuit portions of frequency mixer, for realizing mixing function; Right-hand component is local oscillator driving circuit section, for amplifying and adjustment local oscillation signal.The utility model adopts the topological structure based on Gilbert type element circuit, and uses BiCMOS technique to design.First use four bipolar transistors as switching tube, and adopt RC parallel circuits as load stage circuit, total is the input of difference local oscillation signal and difference radio-frequency signal input, carries out the output of middle frequency difference sub-signal after completing mixing work.If rear end needs to carry out single-ended signal process, then add one-level double-end signal again and process to the change-over circuit of single-ended signal.And frequency mixer front end is all generally low noise amplifier module circuit in receivers, the radiofrequency signal that antenna receives is processed and outputs to the radio-frequency (RF) signal input end of frequency mixer.
In Fig. 5, Vdd represents supply voltage, and Iref2 is reference current, and R4, R9, R10 and R11 are divider resistance; Transistor M6, M7 form mirror current source, and transistor M8-M13 is mirror current source part.Resistance R5-R8 is protective resistance respectively, and V1 is the base bias voltage of bipolar transistor Q1 and Q4, and V2 is the base bias voltage of Q2 and Q3, V3 and V4 is the gate bias voltage of transconductance stage transistor M3 and M4 respectively.R2, C1 and R3, C2 form two parallel circuitss respectively as load stage circuit.Bipolar transistor Q1-Q4 is the switch amplifier transistor of switching stage circuit, I1 and I2 is Injection Current source, LO+ and LO-represents the local oscillator input signals of difference respectively, IF+ and IF-represents the IF output signal of difference, transistor M3 and M4 forms transconductance stage circuit, RF+ and RF-represents the radio-frequency input signals of difference respectively.Iref1 is reference current source, and R1 is divider resistance, and transistor M1, M2 and M5 are image current source transistor, composition frequency mixer tail current source circuit.R12-R15 is the load resistance of local oscillator driving circuit section, LOIN is single-ended local oscillator input signals, bipolar transistor Q5, Q6 form first order amplifying circuit, I3 is tail current source, and R16 is Input matching resistance, and electric capacity C3 and Q5, Q6 complete the conversion of single-ended local oscillator input signals to differential signal, bipolar transistor Q7 and Q8 forms second level amplifying circuit, I4 is tail current source, and LO+ and LO-is difference local oscillator output signal, and Vdd is supply voltage.
In an embodiment, radio-frequency input signals scope of the present utility model is 2.1GHz-2.5GHz, and local oscillator input signals scope is 2.3GHz-3GHz, and concrete frequency is selected according to the actual requirements.
Fig. 6 is circuit structure block diagram of the present utility model, and primarily of local oscillator drive circuit, load stage circuit, switching stage circuit, transconductance stage circuit is formed.Single-ended local oscillation signal amplifies through local oscillator drive circuit and transfers difference output to switching stage circuit, and with the radio-frequency differential signal mixing from transconductance stage circuit, being converted to current intermediate frequency signal through load stage circuit conversion is that voltage intermediate frequency signal exports.
In Fig. 6, LOin represents local oscillator input signals, and RFin represents radio-frequency input signals, and IFout represents IF output signal.
Fig. 7 is application circuit structure chart of the present utility model, first the local oscillation signal produced by local oscillation signal generator or the local oscillation signal produced by phase-locked loop circuit enter local oscillator drive circuit to carry out local oscillation signal shaping and amplifies process, afterwards the local oscillation signal that local oscillator drive circuit is handled well is input to the local oscillator input port of active mixer, radiofrequency signal after low noise amplifier process is input to the rf inputs mouth of active mixer, complete mixing function in active mixer module, and carry out the output of middle frequency difference sub-signal; If desired single-ended intermediate-freuqncy signal, then add the change-over circuit of one-level double-end signal to single-ended signal after frequency mixer.In the embodiment of application circuit of the present utility model, single-ended local oscillator input signals enters local oscillator drive circuit, complete single-ended signal to the conversion of both-end differential signal and amplification work, then enter frequency mixer and differential radio frequency input signal carries out mixing, and export middle frequency difference sub-signal.
In Fig. 7, LOin represents single-ended local oscillator input signals, and outp and outn represents difference local oscillator output signal, RFin represents radio-frequency input signals, out represents radio frequency output signal, and IFoutp and IFoutn represents difference IF output signal, and IFout represents single-ended IF output signal.
The above; be only embodiment of the present utility model; but protection range of the present utility model is not limited thereto; anyly be familiar with those skilled in the art in the utility model scope of disclosure; the change that can expect easily or replacement, all should be encompassed in the protection range of the utility model claim.