CN101794368A - logarithmic amplifier - Google Patents
logarithmic amplifier Download PDFInfo
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- CN101794368A CN101794368A CN200910185215A CN200910185215A CN101794368A CN 101794368 A CN101794368 A CN 101794368A CN 200910185215 A CN200910185215 A CN 200910185215A CN 200910185215 A CN200910185215 A CN 200910185215A CN 101794368 A CN101794368 A CN 101794368A
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Abstract
The invention relates to a logarithmic amplifier with high precision, low power consumption and large dynamic range. The logarithmic amplifier comprises a voltage-current converting input stage, a current-voltage converting output stage and a constant-current source. The logarithmic amplifier is characterized in that the voltage-current converting input stage is composed of five-stage linear logarithmic amplifiers in a cascading manner, each stage of linear logarithmic amplifier contains an amplification stage and a transconductance stage, and the output current of each transconductance stage is converted to output voltage through the current-voltage converting output stage so as to provide the biased constant-current source, frequency compensation and the like for the circuit. Each stage of amplification factor of the logarithmic amplifier is reasonably designed, thus increasing the dynamic range of the circuit; the constant-current source is elaborately designed, thus increasing logarithmic precision, reducing the power consumption of the circuit; and a detuning adjustment end and a slope adjustment end are stalled. The logarithmic amplifier of the invention is characterized by small size, wide dynamic range, low power consumption, high precision, flexible operation and the like.
Description
Technical field
The present invention relates to a kind of logarithmic amplifier, particularly the logarithmic amplifier of semiconductor integrated technology formation.
Background technology
Logarithmic amplifier commonly used is divided into basic logarithmic amplifier, base band logarithmic amplifier, demodulating logarithmic amplifier, and they respectively have relative merits.
Basic logarithmic amplifier also claims the transconductance linearity logarithmic amplifier, and it realizes the log-transformation of signal based on the log characteristic of bipolarity triode (BJT).This class logarithmic amplifier can respond the input signal of slow variation, is characterized in having the good DC precision and the dynamic range of non-constant width, and shortcoming is that AC characteristic is poor.
The base band logarithmic amplifier also claims video logarithmic amplifier, and it has overcome the shortcoming of basic logarithmic amplifier, can respond fast-changing input, and AC characteristic is good, but dynamic range is less.
Demodulating logarithmic amplifier also claims detection logarithmic amplifier step by step, can obtain good logarithm transmission characteristic, but often power consumption is bigger, basically greater than 30mA.
Therefore above-mentioned logarithmic amplifier can't satisfy fields such as mobile base station, the processing of wide multidate information, electronic surveying for high precision, low-power consumption, the big dynamically demand of logarithmic amplifier.
Summary of the invention
The object of the present invention is to provide a kind of precision height, low in energy consumption, wide dynamic range, and the adjustable logarithmic amplifier integrated circuit of log slope.
The technical solution that realizes the object of the invention is:
A kind of logarithmic amplifier, comprise electric current and voltage conversion input stage, current/voltage conversion output stage and constant current source, it is characterized in that electric current and voltage conversion input stage is made up of Pyatyi line log amplifier cascade system, every grade of line log amplifier has amplifier stage and transconductance stage, and the output current of each transconductance stage is converted to output voltage by current/voltage conversion output stage.
Core of the present invention is to come the piecewise linear approximation logarithmic function with a plurality of identical linear amplifier cascades.Be provided with a desirable switched current source, when input voltage during less than L output current be zero; When input voltage during more than or equal to L, output current I1.If N level perfect switch current source is formed electric current and voltage conversion input stage, except the first order, all the other every grade all has voltage amplifier, and voltage amplification factor is A.After the N level current source series connection input voltage is amplified step by step, then when input voltage was X (n)=L/An, it was (N-n) * I that N-n level output current is arranged
1Like this, on each saturation point, output current Y (n) is the function of input voltage X (n).Relational expression between derivation output and the input current voltage:
By: Y (n)=(N-n) * I
1, X (n)=L/A
n
Get Y=(N-n) I
1=[N+ (lnX-lnL)/lnA] * I
1
＝I
1*[N-1/lnA*lnL+1/lnA*lnX]＝P+Q*lnX
Promptly
Y＝P+Q*lnX
So just finished the logarithm function, as shown in Figure 6.
The present invention compared with prior art, its remarkable advantage is:
1. dual power supply is optimized circuit performance and low in energy consumption: 6～9V ,≤14mA;
2. the rise time is fast :≤15ns;
3. wide dynamic range: 〉=60dB;
4. wide input voltage range: 0.6mV～250mV
5. logarithm precision height :≤1dB;
6. bandwidth range is wide: 〉=67Mhz
7. noise is low :≤50 μ V
8. Gain Adjustable is put in order, can be compensated offset voltage.
Description of drawings
Fig. 1 is a logarithmic amplifier circuit block diagram of the present invention;
Fig. 2 is the schematic diagram of electric current and voltage conversion input stage in the logarithmic amplifier circuit of the present invention;
Fig. 3 is the circuit diagram of amplifier stage in the logarithmic amplifier circuit of the present invention;
Fig. 4 is the circuit structure diagram of constant current source in the logarithmic amplifier circuit of the present invention;
Fig. 5 is the circuit structure diagram of current/voltage conversion output stage in the logarithmic amplifier circuit of the present invention;
Fig. 6 is that switched current source input voltage and output current concern synoptic diagram.
Embodiment
Below in conjunction with accompanying drawing the present invention is described in further detail:
In conjunction with Fig. 1, by block diagram as can be seen circuit mainly partly form by electric current and voltage conversion input stage, current/voltage conversion output stage, constant current source, frequency compensated circuit etc.
Electric current and voltage conversion input stage circuit is realized the conversion of linear voltage to non-linear current, and promptly the voltage transitions of great dynamic range is the electric current of small dynamic range.The first order has the balance adjustment function in the input stage of electric current and voltage conversion input stage circuit, can improve the output characteristics under the small-signal.
Current/voltage conversion output-stage circuit is realized the conversion of electric current to voltage, adopts wilson current mirror in the current/voltage conversion output-stage circuit, suppresses the symmetry influence of output voltage variation to current mirror.Constant current source provides stable bias current for circuit, and the baseline impact in the constant-current source circuit is to the maximal value of output, ten octave slopes of curve of output.The temperature characterisitic that guarantees circuit is good, and constant current source must not vary with temperature.Constant-current source circuit produces part by current reference and temperature compensation division is grouped into.
Frequency compensated circuit adopts external compensation, on circuit is realized, has introduced the Miller capacitance lag compensation between P13 in Fig. 5 and output.
In conjunction with Fig. 2, in order to improve input voltage range, make circuit can respond the following signal of mV, require the circuit small-signal gain very big, it is fast that response is wanted, and therefore the input stage structural design proposed high requirement, and the I and II amplifier can't meet the demands separately.Requirement in conjunction with input voltage range and slewing rate, the input stage structure adopts Pyatyi line log amplifier cascade system, every grade of amplifier has amplifier stage and transconductance stage D, the output current of each transconductance stage, be converted to output voltage V out by current/voltage conversion output stage, enlargement factor is designed to about 15dB, has so both satisfied the gain requirement of small-signal, wide dynamic range has improved response speed again.
To reach logarithm precision≤1dB in addition, need circuit to have higher logarithm conversion characteristic and good log slope, so the enlargement factor of mutual conductance amplification input stage is consistent, the saturation point of transconductance stage and amplifier stage is identical, the size of constant current source is consistent, guarantees that slope is identical.
In conjunction with Fig. 3, each grade amplifier has amplifier stage and transconductance stage, and Q1 and R1 are amplifier stage, and Q3 and R3 form transconductance stage, and Q5 and R5, Q6 and R6 are respectively amplifier stage and the corresponding constant current source of crossgrade.Relational expression between amplifier stage output voltage and the input voltage:
Vdo＝-R1*I0*((exp(Vin/VT)-1)/((exp(Vin/VT)+1)
Voltage amplification factor is during small-signal
A＝-R1*I0/(2VT)
Wherein I0 is the constant current source electric current of amplifier stage, and R1 is a pull-up resistor.
When large-signal, amplifier stage is because of current saturation, and maximum output voltage is Vmax=R1*I0
The input voltage of transconductance stage and output current relation satisfy following equation:
Vin＝VTlnλ+(λ-1)R3*I1/(λ+1)
Ido＝(λ-1)Ib
I1＝(λ+1)Ib
Wherein λ is the ratio of the output current of transconductance stage two differential driving pipes, i.e. λ=Ia/Ib, and Ido is the difference output current, I1 is the constant current source electric current.
When Vin was small-signal, the transconductance stage mutual conductance was: g=1/R3
When Vin was large-signal, the transconductance stage output current was saturated, and output current is I1.
Figure knows according to foregoing circuit, and transconductance stage could be saturated after amplifier stage is saturated, and transconductance stage input voltage when saturated is Vosat=I1*R3.The saturated output voltage of amplifier stage is I0*R1.Consider from phase shift and noise two aspects, in the circuit design, the amplifier stage constant current source is designed to 2 times of transconductance stage constant current source, i.e. I0=2*I1.Therefore in order to make amplifier stage saturated before transconductance stage, R1 should be less than half of R3.
In conjunction with Fig. 4, the constant current source baseline impact of this circuit is to the maximal value of output, ten octave slopes of curve of output.The temperature characterisitic that guarantees circuit is good, and constant current source must not vary with temperature.
The constant current source of this circuit produces part by current reference and temperature compensation division is grouped into.Current reference produces in the part, adopts current mirror, utilizes the Current Negative Three-Point Capacitance effect of emitter resistance in series, makes that the collector current of current reference is equal fully.According to the voltage and current equilibrium relation, emitter current I2 satisfies following relational expression as can be known:
I2*R139＝VT*ln6
So, I2=VTln6/R139=(kT/q) * ln6/R139.Under the normal temperature, VT=26mV gets I2=204uA, and I2 is the current source that is directly proportional with temperature.
The temperature compensation of constant current source partly is the opposite principle of temperature coefficient of utilizing triode Q081 and resistance R 138.Because resistance is directly proportional with temperature, has positive temperature coefficient (PTC); And the voltage on the triode has negative temperature coefficient, temperature coefficient is-and 2.32mV/ ℃.So select suitable resistance can reach the purpose of temperature compensation.
For easy to use, circuit is provided with slope adjustment end P9 in addition, by changing the size of constant current source, can adjust log slope easily.Circuit is provided with imbalance and adjusts end, can eliminate the influence that imbalance brings like this.
The output of constant current source is vbias, and is corresponding with the input of mutual conductance part among Fig. 3.
In conjunction with Fig. 5, switching current IN1, the IN2 that input stage produces is by the input of PNP pipe emitter, export from collector, realize impedance conversion, the inner common base darlington structure that adopts of circuit, so that the raising current amplification factor, make that current amplification factor meets design requirement under the high frequency, can improve cutoff frequency simultaneously.Q19 and Q020 realize that the electric current both-end is input to the conversion of single-ended output.Q81, Q82 are wilson current mirror, adopt wilson current mirror, suppress the symmetry influence of output voltage variation to current mirror.
The biased electrical of Darlington fails to be convened for lack of a quorum influences the power consumption of output and the linearity of output.Bias current has determined the resistance in series of its emitter.In order to guarantee the linearity, emitter impedance is more much smaller than resistance in series.In order to reduce circuit power consumption, this resistance also will be selected meticulously.
Claims (1)
1. logarithmic amplifier, comprise electric current and voltage conversion input stage, current/voltage conversion output stage and constant current source, it is characterized in that electric current and voltage conversion input stage is made up of Pyatyi line log amplifier cascade system, every grade of line log amplifier has amplifier stage and transconductance stage, and the output current of each transconductance stage is converted to output voltage by current/voltage conversion output stage.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN200910185215A CN101794368A (en) | 2009-10-30 | 2009-10-30 | logarithmic amplifier |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN200910185215A CN101794368A (en) | 2009-10-30 | 2009-10-30 | logarithmic amplifier |
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| CN101794368A true CN101794368A (en) | 2010-08-04 |
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|---|---|---|---|
| CN200910185215A Pending CN101794368A (en) | 2009-10-30 | 2009-10-30 | logarithmic amplifier |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016066075A1 (en) * | 2014-10-30 | 2016-05-06 | 华为技术有限公司 | Ultra-low working voltage rail to rail operational amplifier and differential input amplification-stage circuit and output-stage circuit thereof |
| US9927469B2 (en) | 2014-12-22 | 2018-03-27 | Microsemi Corporation | Log-linear power detector |
| CN109525277A (en) * | 2017-09-18 | 2019-03-26 | 综合器件技术公司 | Establish asymmetric transmission/reception switch method with 90 degree of impedance transformation sections |
-
2009
- 2009-10-30 CN CN200910185215A patent/CN101794368A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016066075A1 (en) * | 2014-10-30 | 2016-05-06 | 华为技术有限公司 | Ultra-low working voltage rail to rail operational amplifier and differential input amplification-stage circuit and output-stage circuit thereof |
| US10270391B2 (en) | 2014-10-30 | 2019-04-23 | Huawei Technologies Co., Ltd. | Ultra-low working voltage rail-to-rail operational amplifier, and differential input amplification-stage circuit and output-stage circuit thereof |
| US9927469B2 (en) | 2014-12-22 | 2018-03-27 | Microsemi Corporation | Log-linear power detector |
| CN109525277A (en) * | 2017-09-18 | 2019-03-26 | 综合器件技术公司 | Establish asymmetric transmission/reception switch method with 90 degree of impedance transformation sections |
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Application publication date: 20100804 |