CN205566231U - Radio frequency amplifier with adjustable gain - Google Patents

Abstract

The utility model discloses a radio frequency amplifier with adjustable gain, it includes NMOS pipe NM1, the 2nd NMOS manages NM2, the 3rd NMOS manages NM3, first electric capacity C1, second electric capacity C2, third electric capacity C3, fourth electric capacity C4, first resistance R1, first inductance L1, second inductance L2, an offset voltage VB1, the 2nd offset voltage VB2, the 3rd offset voltage VB3, fourth offset voltage VB4 and mains voltage RFVDD. Compared with the prior art, the utility model discloses increase a feedback circuit on traditional fixed gain amplifier's circuit structure, realize through this feedback circuit that the gain is adjustable, expanded the usage scope of this amplifier greatly, set up a bias circuit through the bars level department at NMOS pipe NM1, mainly used adjusts input impedance and matees, the wholeness ability of improved circuit sensitivity and this amplifier.

Description

Adjustable gain formula radio frequency amplifier

Technical field

This utility model relates to the radio frequency amplifier of a kind of adjustable gain formula, belongs to radio frequency in RFID reader and puts Big device technical field.

Background technology

RFID reader performance, along with the development of RFID technique, is had higher requirement by recent years, More pay close attention to the performance of chip, and the index such as power consumption and cost.And radio-frequency front-end amplifier is as RFID Important module in card reader, its characteristic also determine the performance of whole receiver module, such as noise and sensitive Degree etc..It is the lowest that radio frequency amplifier requires have certain gain noise simultaneously, thus suppresses mixing The noise of the subsequent module such as device, the final sensitivity improving whole RFID reader.Traditional radio frequency amplifier In, gain is all fixing, and some system then needs the pattern of adjustable gain.Such as should at rfid system In with, remote time near during label, the overall gain that whole system requires needs exist for change, additionally in card reader also Requirement has monitoring pattern and reading mode, and for reading mode, sensitivity requirement is relatively low, and for monitoring Pattern, then require higher sensitivity.

The major parameter of performance describing radio frequency amplifier has: noise coefficient, voltage gain, inputs and exports Loss, reverse isolation degree and the linearity etc..Owing to these parameters are restrictions interrelated, mutual, because of Which kind of compromise proposal this uses become the Major Difficulties of design to the overall performance improving amplifier.Prior art In the circuit diagram of radio frequency amplifier as it is shown in figure 1, its gain is changeless so that amplifier is at certain A little occasions cannot be applied.

Utility model content

Therefore, for above-mentioned problem, the utility model proposes the radio frequency amplifier of a kind of adjustable gain formula, Existing circuit base improves, adds the function of adjustable gain so that the purposes of amplifier is more Add is extensive, to solve the deficiency of prior art.

To achieve these goals, realization approach of the present utility model is, adds at outfan and input Feedback circuit, when needs high-gain mode of operation, switching tube is shut off feedback function, when needs low gain During pattern, turn on feedback circuit, reduce the gain of integrated circuit.In addition to regulation input impedance matching, Also increase by one group of biasing circuit.

Concrete, this utility model be employed technical scheme comprise that, a kind of adjustable gain formula radio frequency amplifier, Including the first NMOS tube NM1, the second NMOS tube NM2, the 3rd NMOS tube NM3, the first electricity Hold C1, the second electric capacity C2, the 3rd electric capacity C3, the 4th electric capacity C4, the first resistance R1, the first inductance L1, Second inductance L2, the first bias voltage VB1, the second bias voltage VB2, the 3rd bias voltage VB3, Four bias voltage VB4 and supply voltage RFVDD；The top crown of described first electric capacity C1 connects radiofrequency signal Input RFIN, the bottom crown of described first electric capacity C1 and one end of the first resistance R1, the 3rd NMOS The source electrode of pipe NM3 and the grid of the first NMOS tube NM1 connect, and the other end of the first resistance R1 is even Meeting the first bias voltage VB1, the grid of the 3rd NMOS tube NM3 connects the 3rd bias voltage VB3, the The bottom crown of three electric capacity C3 and one end of the first inductance L1, the top crown of the second electric capacity C2 and the 2nd NMOS The drain electrode of pipe NM2 connects, another termination supply voltage RFVDD of described first inductance L1, the second electric capacity The bottom crown of C2 connects RF signal output RFOUT, and the grid of the second NMOS tube NM2 connects the Two bias voltage VB2, the source electrode of the second NMOS tube NM2 connects the drain electrode of the first NMOS tube NM1, The grid of the first NMOS tube NM1 and the source electrode of the 3rd NMOS tube NM3, the lower pole of the first electric capacity C1 One end of plate and the first resistance R1 connects, the source electrode of the first NMOS tube NM1 and the one of the second inductance L2 End connects, the other end ground connection of the second inductance L2, and the top crown of described 4th electric capacity meets supply voltage RFVDD, The bottom crown ground connection of the 4th electric capacity.

In order to regulate input impedance matching, this adjustable gain formula radio frequency amplifier also includes one group by the second resistance R2 and the 4th NMOS tube NM4 biasing circuit in series, concrete, one end of the second resistance R2 It is connected with the grid of the first NMOS tube NM1, the other end of the second resistance R2 and the 4th NMOS tube NM4 Drain electrode connect, the source ground of the 4th NMOS tube NM4, the grid of the 4th NMOS tube NM4 is even Connect the 4th bias voltage VB4, the source ground of the 4th bias voltage VB4.3rd NMOS tube NM3 pipe Input and output side with the 3rd electric capacity C3 is connected to this amplifier, constitutes the feedback circuit of amplifier, logical Cross described feedback circuit and realize adjustable gain.

Further, for the impedance in more precise control feedback control loop, this adjustable gain formula radio frequency amplifies Device also includes that one end of the 3rd resistance R3, the 3rd resistance R3 connects the drain electrode of the 3rd bias voltage VB3, the The other end of three resistance R3 connects the top crown of the 3rd electric capacity C3.

In foregoing circuit, the first metal-oxide-semiconductor NM1 is common source input pipe, for the signal input part of amplifier, Second metal-oxide-semiconductor NM2 is cascade pipe, for improving the gain of circuit and eliminating the Miller effect, the Three metal-oxide-semiconductor NM3 are a switching tube, and the size of grid terminal voltage determines the on an off of feedback circuit, when instead During current feed circuit conducting, MOS is equivalent to again a resistance, determines the size of feedback, and the 3rd resistance R3 is auxiliary Resistance, contributes to more accurately controlling the resistance value of feedback control loop.Electric capacity C3 is feedback capacity, the first resistance R1 is biasing resistor, the second inductance L2 be source degeneration resistor, beneficially input impedance coupling and The coupling of whole circuit noise coefficient, the first inductance L1 is load inductance, improves the equivalent negative in respective frequencies Carrying, C1 and C2 is input and output capacitance.Second resistance R2 is biasing resistor, the 4th metal-oxide-semiconductor NM4 is switching tube, and C4 is power filtering capacitor.

This utility model achieves a kind of adjustable gain formula radio frequency amplifier, for 900MHz or 2.4GHz RFID reader in.Compared with prior art, this utility model is at the circuit of tradition fixed gain amplifier Increase a feedback circuit in structure, realize adjustable gain by this feedback circuit, be greatly expanded this amplification The purposes scope of device；By setting up a biasing circuit at the grid level of the first NMOS tube NM1, mainly For regulating input impedance matching, improve circuit sensitivity and the overall performance of this amplifier.Meanwhile, this reality By novel simple in construction, it is easy to accomplish, there is good practicality.

Accompanying drawing explanation

Fig. 1 is the circuit theory diagrams of the radio frequency amplifier mentioned in background technology；

Fig. 2 is the circuit theory diagrams of adjustable gain formula radio frequency amplifier of the present utility model.

Detailed description of the invention

In conjunction with the drawings and specific embodiments, this utility model is further illustrated.

The utility model discloses a kind of adjustable gain formula radio frequency amplifier, be applied to 900MHz or In the RFID reader of 2.4GHz.In traditional radio frequency amplifier, gain is the most changeless, And in the application of RFID, the change in location of label can be big especially, may be just on card reader surface, it is also possible to Distance card reader ten meters is remote.Therefore for this kind of RFID reader, it is necessary to the gain of whole system is multistage Adjustable, thus adapt to the application of various distance.This utility model proposes one to solve the problems referred to above The radio frequency amplifier of adjustable gain formula, it is achieved that gain continuously adjustabe, and range of accommodation is relatively big, prime radio frequency The adjustable gain of amplifier, it is meant that can preferably optimize the performance indications of whole system.

As a specific embodiment, adjustable gain formula radio frequency amplifier of the present utility model and accompanying drawing 2 institute The circuit shown has identical circuit structure.Seeing Fig. 2, a kind of adjustable gain formula of the present utility model is penetrated Audio amplifier, including the first NMOS tube NM1, the second NMOS tube NM2, the 3rd NMOS tube NM3, 4th NMOS tube NM4, the first electric capacity C1, the second electric capacity C2, the 3rd electric capacity C3, the 4th electric capacity C4, First resistance R1, the second resistance R2, the 3rd resistance R3, the first inductance L1, the second inductance L2, first Bias voltage VB1, the second bias voltage VB2, the 3rd bias voltage VB3, the 4th bias voltage VB4 And supply voltage RFVDD；The top crown of described first electric capacity C1 connects radio-frequency (RF) signal input end RFIN, institute State the bottom crown of the first electric capacity C1 and one end of the first resistance R1, the source electrode of the 3rd NMOS tube NM3, One end of second resistance R2 and the grid of the first NMOS tube NM1 connect, the other end of the first resistance R1 The drain electrode of the other end and the 4th NMOS tube NM4 that connect the first bias voltage VB1, the second resistance R2 connects Connecing, the grid of the 4th NMOS tube NM4 connects the 4th bias voltage VB4, the 4th bias voltage VB4's Source ground, the grid of the 3rd NMOS tube NM3 connects the 3rd bias voltage VB3, the 3rd bias voltage The drain electrode of VB3 connects one end of the 3rd resistance R3, and the other end of the 3rd resistance R3 connects the 3rd electric capacity C3 Top crown, the bottom crown of the 3rd electric capacity C3 and one end of the first inductance L1, the upper pole of the second electric capacity C2 The drain electrode of plate and the second NMOS tube NM2 connects, another termination supply voltage of described first inductance L1 The bottom crown of RFVDD, the second electric capacity C2 connects RF signal output RFOUT, the second NMOS tube The grid of NM2 connects the second bias voltage VB2, source electrode the oneth NMOS of the second NMOS tube NM2 The drain electrode of pipe NM1, the grid of the first NMOS tube NM1 and one end of the second resistance R2, the 3rd NMOS One end of the source electrode of pipe NM3, the bottom crown of the first electric capacity C1 and the first resistance R1 connects, a NMOS One end of the source electrode of pipe NM1 and the second inductance L2 connects, the other end ground connection of the second inductance L2, and described the The top crown of four electric capacity connects supply voltage RFVDD, the bottom crown ground connection of the 4th electric capacity.

In above-mentioned adjustable gain formula radio frequency amplifier structure, NM1 is common source input pipe, and NM2 is cascade Pipe, NM3 is switch resistance pipe, and NM4 is control pipe, and C1 is input capacitance, and C2 is for exporting every directly Electric capacity, C3 is feedback capacity, and C4 is filter capacitor, and L1 is load inductance, and L2 is source series inductance, R1 is biasing resistor, and R2 is biasing resistor.NM3 and C3 is connected to the input and output side of amplifier, structure Become the feedback circuit of amplifier.R2 and NM4 constitutes input impedance matching conditioned circuit, R2 and NM4 Can need to be adjusted in order to there is more preferable input impedance according to impedance matching so that input loss Minimum.

Refering to Fig. 2, population structure of the present utility model have employed cascode structure, and input uses common source defeated Enter, and use source negative feedback inductor to optimize input coupling and the noise-figure performance of circuit.By little letter Number analysis can obtain input impedance formula:

$Z_{in}=L_{g}s+\frac{1}{C_{gs1}s}+\frac{g_{m1}L}{C_{gs1}};$

In formula, wherein, g_m1It is the mutual conductance of the first NMOS tube NM1 pipe, C_gs1It it is the first NMOS tube The gate-source parasitic capacitance of NM1 pipe, L is source negative feedback inductor.When resonant frequency and operating frequency are coincide, Input impedance now isBy size and the inductance value size of appropriate design transistor, permissible Preferably inputted coupling, certainly there is also the need to additionally consider pad parasitic capacitance and esd protection circuit The parasitic capacitance impact on circuit.

When normally working, radio frequency voltage signal flows to the first NMOS tube NM1 by the first electric capacity C1, and Radio frequency voltage signal is converted into current radio frequency signal；Then, the current radio frequency signal after conversion flows through second NMOS tube NM2, and produce a voltage signal on the first inductance L1；Then, this voltage signal passes through Second electric capacity C2 output.Preferably, the second bias voltage VB2 of the second NMOS tube NM2 Connecting supply voltage, the first bias voltage VB1 of the first NMOS tube NM1 can select according to circuit performance Select a suitable voltage.

When circuit needs adjustable gain, can be controlled by the feedback circuit between input and output side. Concrete, when grid voltage that is the 3rd bias voltage VB3 of the 3rd NMOS tube NM3 is < during VB1+Vth (Vth is threshold voltage), the 3rd NMOS tube NM3 turns off, i.e. cuts off feedback circuit, now, circuit Overall gain is maximum.As VB3 > VB1+Vth time, the 3rd NMOS tube NM3 conducting, be operated in deep audion District, now, the 3rd NMOS tube NM3 is just equivalent to a resistance so that a part of signal feedback of output To input, thus reduce the gain of circuit, it is achieved adjustable gain.Described 3rd electric capacity C3 is feedback electricity Resistance, is used for hindering the logical exchange of direct current.Therefore, when the 3rd NMOS tube NM3 is operated in deep triode region, its The resistance of equivalence is:

$R_{\mathrm{on}}=\frac{1}{K\frac{W}{L}(\mathrm{VB}3-\mathrm{VB}1-V_{\mathrm{th}})};$

Wherein, K is the 3rd NMOS tube NM3 coefficient, and W/L is the wide long of the 3rd NMOS tube NM3 Ratio.From above formula, when the 3rd bias voltage VB3 is the biggest, the 3rd NMOS tube NM3 conducting is the most strict Evil, its equivalent resistance is the least, and circuit overall gain is the least.Thus can be reached by regulation VB3 Arrive the function of adjustable gain.It addition, the 3rd resistance R3 is for the resistance in more precise control feedback control loop Resist and arrange.

Compared with prior art, adjustable gain formula radio frequency amplifier of the present utility model has the excellent of adjustable gain Point, being simultaneously entered impedance matching can also mate as required, is greatly expanded its use.

Although specifically show and describe this utility model in conjunction with preferred embodiment, but the technology of art Personnel should be understood that in the spirit and scope of the present utility model limited without departing from appended claims, This utility model can be made a variety of changes in the form and details, be protection model of the present utility model Enclose.

Claims (3)

1. an adjustable gain formula radio frequency amplifier, it is characterised in that: include the first NMOS tube NM1, second NMOS tube NM2, the 3rd NMOS tube NM3, the first electric capacity C1, the second electric capacity C2, the 3rd electricity Hold C3, the 4th electric capacity C4, the first resistance R1, the first inductance L1, the second inductance L2, the first biasing Voltage VB1, the second bias voltage VB2, the 3rd bias voltage VB3, the 4th bias voltage VB4 and Supply voltage RFVDD；

The top crown of described first electric capacity C1 connects radio-frequency (RF) signal input end RFIN, described first electric capacity C1's Bottom crown and one end of the first resistance R1, the source electrode of the 3rd NMOS tube NM3 and the first NMOS tube The grid of NM1 connects, and the other end of the first resistance R1 connects the first bias voltage VB1；3rd NMOS The grid of pipe NM3 connects the 3rd bias voltage VB3, the bottom crown of the 3rd electric capacity C3 and the first inductance The drain electrode of one end of L1, the top crown of the second electric capacity C2 and the second NMOS tube NM2 connects, described The bottom crown of another termination the supply voltage RFVDD, the second electric capacity C2 of the first inductance L1 connects radio frequency Signal output part RFOUT, the grid of the second NMOS tube NM2 connects the second bias voltage VB2, The source electrode of the second NMOS tube NM2 connects the drain electrode of the first NMOS tube NM1, a NMOS The grid of pipe NM1 and the source electrode of the 3rd NMOS tube NM3, the bottom crown and first of the first electric capacity C1 One end of resistance R1 connects, and the source electrode of the first NMOS tube NM1 and one end of the second inductance L2 connect, The other end ground connection of the second inductance L2, the top crown of described 4th electric capacity meets supply voltage RFVDD, the The bottom crown ground connection of four electric capacity.

Adjustable gain formula radio frequency amplifier the most according to claim 1, it is characterised in that: this adjustable gain formula Radio frequency amplifier also includes the biased electrical in series by the second resistance R2 and the 4th NMOS tube NM4 Road, concrete, one end of the second resistance R2 is connected with the grid of the first NMOS tube NM1, and second The other end of resistance R2 and the drain electrode of the 4th NMOS tube NM4 connect, the 4th NMOS tube NM4 Source ground, the grid of the 4th NMOS tube NM4 connects the 4th bias voltage VB4, the 4th biasing The source ground of voltage VB4.

Adjustable gain formula radio frequency amplifier the most according to claim 1 and 2, it is characterised in that: this gain can Mode radio frequency amplifier also includes that one end of the 3rd resistance R3, the 3rd resistance R3 connects the 3rd bias voltage The drain electrode of VB3, the other end of the 3rd resistance R3 connects the top crown of the 3rd electric capacity C3.