CN103178795A - Difference frequency indicator based on log amplifier - Google Patents

Abstract

The invention discloses a difference frequency indicator based on a log amplifier. The difference frequency indicator comprises a first resistor and a second resistor. A first signal source is input into one end of the first resistor, the other end of the first resistor is respectively connected with the positive pole of a first diode and the negative pole of a second diode, and the negative pole of the first diode and the positive pole of the second diode are connected with an output end of an operational amplifier at the same time to output difference frequency signal voltage. The first diode is in parallel connection with a capacitor. A second signal source is input into one end of the second resistor, and the other end of the second resistor is respectively connected with the positive pole of the first diode, the negative pole of the second diode and the negative polarity input end of the operational amplifier. The positive polarity input end of the operational amplifier is grounded. The difference frequency indicator based on the log amplifier is easy to operate and simple in structure, stable and high-precision difference frequency signals can be conveniently acquired, integration can be easily achieved, circuit cost is reduced, and various needs in practical application are met.

Description

A kind of difference frequency device based on logarithmic amplifier

Technical field

The present invention relates to electronic technology field, particularly a kind of difference frequency device based on logarithmic amplifier.

Background technology

The difference frequency device is nonlinear device, and output signal frequency equals the poor of two frequency input signals.Difference frequency device of the prior art is generally diode difference frequency device, balance difference frequency device and transistor difference frequency device etc., all is comprised of inductance and transformer etc.

The inventor finds to exist at least in prior art following shortcoming and defect in realizing process of the present invention:

1) influence each other more seriously between each loop of above-mentioned difference frequency device, it is also larger that combination frequency is disturbed, and causes the difference frequency signal that gets unstable;

2) discreteness that is subjected to component parameter of above-mentioned difference frequency device affects greatly, but the dynamic range of processing signals is little;

3) difference frequency signal that gets is deamplification, and sensitivity is low, is difficult to satisfy the multiple needs in practical application.

Summary of the invention

The invention provides a kind of difference frequency device based on logarithmic amplifier, this difference frequency device has been avoided the interference of combination frequency, gets the higher difference frequency signal of stability, sees for details hereinafter and describes:

A kind of difference frequency device based on logarithmic amplifier comprises: the first resistance and the second resistance,

One end input first signal source of described the first resistance, the other end of the first resistance connects respectively the anode of the first diode and the negative electrode of the second diode, the negative electrode of described the first diode and described the second diode anode connect the output of operational amplifier simultaneously, output difference frequency signal voltage; Described the first diodes in parallel electric capacity;

One end input secondary signal source of described the second resistance, the other end of described the second resistance connects respectively the negative electrode of the anode of described the first diode, described the second diode and the negative polarity input of described operational amplifier; The positive polarity input end grounding of described operational amplifier.

The beneficial effect of technical scheme provided by the invention is: formed difference frequency device based on logarithmic amplifier by antiparallel diode, operational amplifier and resistance, this difference frequency device processing ease, simple in structure, can get easily the difference frequency signal stable, that precision is high, easily integrated, and reduced circuit cost, enlarged the dynamic range of signal; Can be easy to change the gain of difference frequency device by the resistance of revising the first resistance and the second resistance, can amplify processing to difference frequency signal by the selection to the operational amplifier model, satisfy the multiple needs in the practical application.

Description of drawings

Fig. 1 is the circuit theory diagrams of a kind of difference frequency device based on logarithmic amplifier provided by the invention.

In accompanying drawing, the list of parts of each label representative is as follows:

R ₁: the first resistance; R ₂: the second resistance;

A: operational amplifier; D ₁: the first diode;

D ₂: the second diode; V _o: difference frequency signal voltage;

V ₁: the first signal source; V ₂: the secondary signal source;

C: electric capacity.

Embodiment

For making the purpose, technical solutions and advantages of the present invention clearer, hereby exemplify following examples, and coordinate accompanying drawing to be described in detail as follows:

For fear of the interference of combination frequency, get the higher difference frequency signal of stability, the embodiment of the present invention has proposed a kind of difference frequency device based on logarithmic amplifier, referring to Fig. 1, comprising: the first resistance R ₁With the second resistance R ₂,

The first resistance R ₁An end input first signal source V ₁, the first resistance R ₁The other end meet respectively the first diode D ₁Anode and the second diode D ₂Negative electrode, the first diode D ₁Negative electrode and the second diode D ₂Anode connects the output of operational amplifier A simultaneously, output difference frequency signal voltage V _oThe first diode D ₁Shunt capacitance C;

The second resistance R ₂An end input secondary signal source V ₂, the second resistance R ₂The other end meet respectively the first diode D ₁Anode, the second diode D ₂Negative electrode and the negative polarity input of operational amplifier A; The positive polarity input end grounding of operational amplifier A.

That is, the first diode D ₁With the second diode D ₂Between form the inverse parallel circuit.

Describe the operation principle of this difference frequency device below in conjunction with Fig. 1 in detail, see for details hereinafter and describe:

Because the voltage-current characteristic of diode is

$I_D=I_S(e^{\frac{V_D}{V_S}}-1)---\left(1\right)$

Wherein: I _SReverse saturation current for PN junction; V _SBeing the temperature voltage equivalent, is 27 ° of C of 300K(Celsius temperature in temperature) time be about 26mV; V _DBe conducting voltage.

Work as V _DV _SThe time, Therefore (1) formula can be rewritten as

$I_D=I_S{e}^{\frac{V_D}{V_S}}---\left(2\right)$

Put aside the effect of capacitor C, due to

$I_I=\frac{V_1}{R_1}+\frac{V_2}{R_2}=I_D---\left(3\right)$

Namely $\frac{V_1}{R_1}+\frac{V_2}{R_2}=I_S{e}^{\frac{V_D}{V_S}}---\left(4\right)$

Due to D1 and D2 reverse parallel connection, only consider the absolute value of circuit output,

$V_O=V_D=V_S\ln \frac{1}{I_S}(\frac{V_1}{R_1}+\frac{V_2}{R_2})---\left(5\right)$

Get R ₁=R ₂=R has

$V_O=V_S\ln \frac{1}{I_{S}R}+V_S\ln (V_1+V_2)---\left(6\right)$

By (6) formula as seen, circuit is logarithmic amplifier.Logarithm lnx can expand into progression:

$\ln x={\ln x}_0+\frac{1}{x_0}\frac{(x-x_0)}{1!}-\frac{1}{x_0^2}\frac{{(x-x_0)}^2}{2!}+\·\·\·{\left(\ln x_0\right)}^{\left(n\right)}\frac{{(x-x_0)}^n}{n!}+\·\·\·---\left(7\right)$

By (6) and (7) formula, and only consider its quadratic term, and all coefficients of quadratic term be designated as K:

V’ _O=K（V ₁+V ₂） ² （8）

At V ₁=V _1mSin ω ₁T and V ₂=V _2mSin ω ₂During t, (8) formula can be rewritten into:

V’ _O=K（V _1msinω ₁t+V _2msinω ₂t） ² （9）

(9) formula is launched, and is only considered its cross term:

V” _O=2KV _lmsinω ₁t·V _2msinω ₂t （10）

Utilize product to sum formula (10) formula can be rewritten as

V” _O=2KV _1mV _2m（sin（ω ₁+ω ₂）t+sin（ω ₁-ω ₂）t） （11）

Work as ω ₁And ω ₂Being close high-frequency signal, is also (ω ₁-ω ₂(the ω of)＜＜ ₁+ ω ₂), by the numerical value of the first resistance R 1, the second resistance R 2 and capacitor C reasonably is set, can filtering and frequency (ω ₁+ ω ₂) signal and keep difference frequency (ω ₁-ω ₂) signal, have:

V″′ _O=2KV _1mV _2msin（ω ₁-ω ₂）t） （12）

Namely can get difference frequency signal by (11) formula, this low frequency signal can be used in ultrasonic device or radio, has satisfied the multiple needs in the practical application.This shows, this difference frequency device has been realized the difference frequency function.

During practical application, can be by revising the first resistance R ₁With the second resistance R ₂Resistance change the gain of whole difference frequency device, can amplify processing to difference frequency signal by the selection to the operational amplifier A model, satisfied the multiple needs in the practical application.

Wherein, the difference frequency device that provides of the embodiment of the present invention is with R ₁=R ₂=10k Ω, the first diode D ₁With the second diode D ₂Model be 1N4148, capacitor C=0.01 μ F, the model of operational amplifier A is that OP07 is that example describes.During specific implementation, the embodiment of the present invention does not limit the model of above-mentioned components and parts, all can as long as can complete the components and parts of above-mentioned functions.

Can find out by above-mentioned example the difference frequency device processing ease that the embodiment of the present invention provides, simple in structure, can get easily difference frequency signal, the multiple needs in the practical application have been satisfied, and owing to only adopting the components and parts such as diode, resistance and operational amplifier, avoided the interference of the combination frequency between components and parts, the precision of the difference frequency signal that therefore gets is higher, has stability in essence.

It will be appreciated by those skilled in the art that accompanying drawing is the schematic diagram of a preferred embodiment, the invention described above embodiment sequence number does not represent the quality of embodiment just to description.

The above is only preferred embodiment of the present invention, and is in order to limit the present invention, within the spirit and principles in the present invention not all, any modification of doing, is equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (1)

1. the difference frequency device based on logarithmic amplifier, comprising: the first resistance (R ₁) and the second resistance (R ₂), it is characterized in that,

Described the first resistance (R ₁) an end input first signal source (V ₁), the first resistance (R ₁) the other end meet respectively the first diode (D ₁) anode and the second diode (D ₂) negative electrode, described the first diode (D ₁) negative electrode and described the second diode (D ₂) anode connects the output of operational amplifier (A) simultaneously, output difference frequency signal voltage (V _o); Described the first diode (D ₁) shunt capacitance (C);

Described the second resistance (R ₂) an end input secondary signal source (V ₂), described the second resistance (R ₂) the other end meet respectively described the first diode (D ₁) anode, described the second diode (D ₂) negative electrode and the negative polarity input of described operational amplifier (A); The positive polarity input end grounding of described operational amplifier (A).

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