CN201210058Y - Weak current and voltage conversion circuit - Google Patents

Abstract

The utility model relates to a weak current-to-voltage conversion circuit. The conversion circuit comprises a weak current signal input end (in), and an operational amplifier (A); wherein, the cathode signal input end of the operational amplifier (A) is connected with the signal output end (out) of the operational amplifier (A) through a feedback resistance (Rf). The conversion circuit is characterized in that the weak current signal input end is connected with the anode signal input end of the operational amplifier (A) through a low-noise preset processing circuit. Compared with the prior art, the utility model has the advantage that the serial connection of the low-noise preset processing circuit at the signal input end of the whole machine of the operational amplifier can effectively increase the bandwidth of the whole circuit and reduce the noise gain bandwidth of the circuit.

Description

A kind of weak current voltage conversion circuit

Technical field

The utility model relates to a kind of weak current voltage conversion circuit.

Background technology

In Photodetection system, photo-electric conversion element generally adopts photodiode, by the detection to the photodiode photocurrent, realizes the detection to optical information or out of Memory (as temperature, pressure, tension force etc.).Because the photocurrent very faint (having only pA) of photodiode output to the nA rank, and because circuit noise, element noise, dark current and non-linear etc. influence, accomplish accurately to measure has bigger difficulty.

As described in accompanying drawing 1, use current-to-voltage converting circuit in the existing Photodetection system, generally the current signal input end is linked to each other with the negative input of operational amplifier, the negative input of operational amplifier is by feedback resistance R _fLink to each other with the output terminal of operational amplifier, the electrode input end of operational amplifier then with a resistance R ' link to each other, the output terminal of operational amplifier is voltage signal output end.Under the ideal operational amplifier condition, input resistance is zero, thereby i _F=i _SSo, output voltage V ₀=-i _S* R _f, but in fact, input resistance can not be zero, and feedback resistance R _fNoise ratio bigger, cause the noise gain bandwidth of whole current-to-voltage converting circuit too high, the sensitivity of circuit is not high, precision is not enough.

Consider the influence of the stray capacitance of sensor (photodiode junction capacitance) distributed capacitance and printed circuit board (PCB), after the current signal input end entered current-to-voltage converting circuit, circuit was easy to generate vibration.

The utility model content

Technical problem to be solved in the utility model is to provide a kind of noise gain bandwidth little weak current voltage conversion circuit at above-mentioned prior art.

The utility model solves the problems of the technologies described above the technical scheme that is adopted: this weak current voltage conversion circuit, it includes the low current signal input end, operational amplifier, the negative signal input end of operational amplifier links to each other with the signal output part of operational amplifier by a feedback resistance, it is characterized in that: the low current signal input end links to each other with the positive signal input end of described operational amplifier by a LNA preposing signal process circuit.

The preposing signal process circuit of the LNA that the utility model provides mainly is made up of a LNA field effect transistor, amplification resistance and preposition resistance, wherein the low current signal input end connects first end that amplifies resistance, second end that amplifies resistance links to each other with the grid of described field effect transistor, the drain electrode of described field effect transistor links to each other with the positive signal input end of described operational amplifier after connecting preposition resistance, the drain electrode of described field effect transistor connects cathode power supply simultaneously, and the source electrode of described field effect transistor then connects negative power supply.

In order to eliminate the vibration that feedback resistance produces in the circuit, the two ends of described feedback resistance are parallel with a building-out capacitor.

Compared with prior art, advantage of the present utility model is: by the complete machine signal input part serial connection LNA preposing signal process circuit at operational amplifier, can effectively increase the bandwidth of positive entire circuit, reduce the noise gain bandwidth of circuit.

Description of drawings

Fig. 1 is existing current-to-voltage converting circuit;

Fig. 2 is a weak current voltage conversion circuit among the utility model embodiment.

Embodiment

Embodiment describes in further detail the utility model below in conjunction with accompanying drawing.

Weak current voltage conversion circuit as described in Figure 2, it includes low current signal input end in, operational amplifier A, the negative signal input end of operational amplifier A is by a feedback resistance R _fLink to each other with the signal output part out of operational amplifier A, the low current signal input end links to each other with the positive signal input end of described operational amplifier A by a LNA preposing signal process circuit.Wherein, the preposing signal process circuit of LNA mainly is made up of a LNA field effect transistor TR, amplification resistance R 1 and preposition resistance R 2, low current signal input end in connects first end that amplifies resistance R 1, second end that amplifies resistance R 1 links to each other with the grid of described field effect transistor TR, the drain electrode of described field effect transistor TR connects preposition resistance R 2 backs and links to each other with the positive signal input end of described operational amplifier A, the drain electrode of described field effect transistor TR connects cathode power supply simultaneously, and the source electrode of described field effect transistor TR then connects negative power supply.

Feedback resistance R _fTwo ends be parallel with a building-out capacitor C.

The bandwidth of general current-to-voltage converting circuit can be calculated with following formula:

$f_{-3\mathrm{dB}}=\sqrt{\frac{\mathrm{GPB}}{{2\mathrm{\πR}}_F{C}_D}}\left(\mathrm{Hz}\right)$ Formula (1)

GPB is that the unity gain bandwidth of operational amplifier is long-pending in the formula, R _FBe feedback resistance resistance, C _InFor current-to-voltage converting circuit equivalent input capacitance, in the prior art, current-to-voltage converting circuit equivalent input capacitance be the equivalent input capacitance C of operational amplifier _o

After adopting the technical scheme that the utility model adopted, the equivalent input capacitance of weak current voltage conversion circuit amplifying circuit this moment that the utility model provides

$C_{\mathrm{in}}=\frac{C_o\×C_{\mathrm{gs}}}{C_o+C_{\mathrm{gs}}}$ Formula (3)

In the formula, C _oBe the equivalent input capacitance of operational amplifier, C _GsBe the equivalent capacity of LNA field effect transistor TR, the C of the operational amplifier of selecting for use _oBe generally 2～4pF, C _GsBe generally 10～12pF, by formula (3) as can be known, owing to adopted LNA field effect transistor TR, the actual equivalent input capacitance of amplifying circuit reduces, again according to formula (1), adopt the weak current voltage conversion circuit of LNA field effect transistor TR can increase the bandwidth of circuit effectively as can be known.

In addition, the noise gain bandwidth N of general current-to-voltage converting circuit _FCan directly calculate by following formula:

$N_F=1+\frac{\mathrm{Cin}}{C_F}$ Formula (4)

In the formula, C _InBe the equivalent input capacitance of operational amplification circuit, C _FFor feedback resistance building-out capacitor and circuit board distributed capacitance and stray capacitance sum, by formula (3), can effectively reduce the input capacitance of circuit by serial connection LNA field effect transistor TR, through type (4) can be known, reduces C _In, the noise gain bandwidth N that promptly reduces _F

Claims (3)

1, a kind of weak current voltage conversion circuit, it includes low current signal input end (in), operational amplifier (A), the negative signal input end of operational amplifier (A) links to each other with the signal output part (out) of operational amplifier (A) by a feedback resistance (Rf), it is characterized in that: the low current signal input end links to each other with the positive signal input end of described operational amplifier (A) by a LNA preposing signal process circuit.

2, weak current voltage conversion circuit according to claim 1, it is characterized in that: the preposing signal process circuit of described LNA is mainly by a LNA field effect transistor (TR), amplifying resistance (R1) and preposition resistance (R2) forms, wherein low current signal input end (in) connects first end that amplifies resistance (R1), second end that amplifies resistance (R1) links to each other with the grid of described field effect transistor (TR), the drain electrode of described field effect transistor (TR) connects preposition resistance (R2) back and links to each other with the positive signal input end of described operational amplifier (A), the drain electrode of described field effect transistor (TR) connects cathode power supply simultaneously, and the source electrode of described field effect transistor (TR) then connects negative power supply.

3, weak current voltage conversion circuit according to claim 1 and 2 is characterized in that: the two ends of described feedback resistance (Rf) are parallel with a building-out capacitor (C).