CN107241017B - Balanced differential chopper circuit and isolation amplifier based on same - Google Patents
Balanced differential chopper circuit and isolation amplifier based on same Download PDFInfo
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- CN107241017B CN107241017B CN201710420110.7A CN201710420110A CN107241017B CN 107241017 B CN107241017 B CN 107241017B CN 201710420110 A CN201710420110 A CN 201710420110A CN 107241017 B CN107241017 B CN 107241017B
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- 238000002955 isolation Methods 0.000 title claims abstract description 24
- 230000008878 coupling Effects 0.000 claims description 4
- 238000010168 coupling process Methods 0.000 claims description 4
- 238000005859 coupling reaction Methods 0.000 claims description 4
- 230000001052 transient effect Effects 0.000 description 8
- 238000010586 diagram Methods 0.000 description 7
- 238000010521 absorption reaction Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000003990 capacitor Substances 0.000 description 2
- 230000005669 field effect Effects 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of DC power input into DC power output
- H02M3/02—Conversion of DC power input into DC power output without intermediate conversion into AC
- H02M3/04—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters
- H02M3/10—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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Abstract
The invention discloses a balanced differential chopper circuit and an isolation amplifier based on the same, which are used in the isolation amplifier and comprise a chopper circuit, wherein a chopper tube of the chopper circuit is connected with a chopper tube circuit which forms a differential structure with the chopper circuit, the quality of signals output by the chopper circuit is high, and the precision of the isolation amplifier can be effectively improved.
Description
Technical Field
The invention relates to the field of chopper circuits, in particular to a balanced differential chopper circuit and an isolation amplifier based on the chopper circuit.
Background
The existing transformer isolation amplifier adopting the chopping modulation demodulation mode basically adopts an N-channel FET switching tube as a chopping device. As shown in fig. 1 to 3, the chopper modulation/demodulation respectively adopts the following methods: series chopping, parallel chopping, and series-parallel chopping. Chopping in these ways has two disadvantages, which affect the index of chopping modulation/demodulation.
First, when the transistor is deeply pinched off, the gate-leakage current I of the FET switch tubeGDO. The grid and the channel of the FET switch tube are equivalent to a PN junction diode with reverse bias, so even if a sufficiently large negative grid voltage is deeply pinched off, reverse bias leakage current still exists between the grid-drain and the grid-source. Gate-to-drain current IGDOAt chopping/demodulating load RLVoltage drop generated is equal to IGDORL. When R isLWhen the value is large enough, the value may be relatively large. I isGDOAlso, the temperature is similar to an exponential relationship, and is the main reason for causing the temperature drift of the chopper. Taking the serial chopping which is used more at present as an example, a lower gate-leakage current I is analyzedGDOSimilar to the effect of transient spikes on the output chopped signal, the rest of the circuit. When the series chopping FET switching tube is switched on and switched off, the equivalent circuits are respectively shown in fig. 4 and fig. 5. When the FET switch tube is on, the load voltage Vo1Comprises the following steps:
when the FET switch tube is pinched off, the load voltage Vo2Comprises the following steps: vo2＝IGDORI. Then the DC slowly-varying signal V is inputtedIAlternating signal V generated by series chopperoThe relationship of (1) is:
second, transient spikes. The N-channel FET switch tubes have larger gate-channel junction capacitance, and the value of the gate-channel junction capacitance is between 5 and 25 p. When a chopping driving square wave signal is applied to the grid, the charging and discharging action of the capacitors presents transient spikes at the output end, which is equivalent to generating offset current for a subsequent amplifier. In order to suppress the transient spike, it is common practice to add an RC absorption circuit, but the addition of this circuit will increase the response time of the circuit, deteriorate the amplitude-frequency characteristics, and is not favorable for testing the ac signal.
Due to the two factors, the chopped signal quality is poor, and the precision of the isolation amplifier is affected.
Disclosure of Invention
The invention provides a balanced differential chopper circuit and an isolation amplifier based on the chopper circuit, aiming at solving the technical problems, wherein the chopper circuit has high output signal quality and can effectively improve the precision of the isolation amplifier.
The invention is realized by the following technical scheme:
a balanced differential chopper circuit is used in an isolation amplifier and comprises a chopper circuit, wherein a differential chopper circuit which forms a differential structure with the chopper circuit is connected to the ground end of a chopper tube of the chopper circuit.
The inventors have found in studies on chopper circuits that to solve the above-mentioned problem of poor quality of the output signal after chopping due to chopper temperature drift and transient spikes, the above-mentioned effects are most effectively suppressed by using a differential structure. After the structure is adopted, transient peaks are in a common mode, and are effectively suppressed after entering a subsequent isolation amplifier, an RC (resistor-capacitor) absorption network is not needed, and the amplitude-frequency characteristic can be greatly improved.
Preferably, the chopper circuit is a parallel chopper circuit, the parallel chopper circuit includes a first resistor connected between the input signal terminal and the first load connection terminal, and a first chopper tube connected between the first load connection terminal and the ground terminal, the differential chopper circuit includes a second chopper tube connected between the ground terminal and the second load connection terminal, and a second resistor connected between the second load connection terminal and the ground terminal, and the first resistor and the second resistor have equal resistance values.
Further, the first chopper tube and the second chopper tube are both N-channel field effect transistors.
Preferably, the chopper circuit is a series-parallel chopper circuit, and the series-parallel chopper circuit includes a third resistor, a third chopper tube, a fourth resistor, and a fourth chopper tube, which are sequentially connected between an anode of the input signal terminal and the first load connection terminal; the differential chopper circuit comprises a fifth resistor, a fifth chopper tube and a sixth resistor which are sequentially connected between the cathode of the input signal end and the second load connecting end, and a sixth chopper tube connected between the ground end and the second load connecting end, wherein the third resistor and the fifth resistor have the same resistance value, and the fourth resistor and the sixth resistor have the same resistance value.
An isolation amplifier comprises the differential chopper circuit and an isolation amplifier connected at the output end of the differential chopper circuit, wherein the isolation amplifier is an alternating current amplifier with differential input or a coupling transformer with a center tap.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the chopper tube circuit is connected with the chopper tube of the existing parallel chopper circuit to form a differential structure with the parallel chopper circuit, so that the influence caused by temperature drift and transient peak of the chopper is counteracted, the quality of the output signal after chopping is high, and the precision of the isolation amplifier can be effectively improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
fig. 1 is a schematic circuit diagram of a conventional series chopper modulation/demodulation circuit.
Fig. 2 is a schematic circuit diagram of a conventional parallel chopper modulation/demodulation circuit.
Fig. 3 is a schematic circuit diagram of a conventional series-parallel chopper modulation/demodulation circuit.
FIG. 4 is an equivalent diagram of a conventional series chopper modulation/demodulation chopper tube when it is turned on.
FIG. 5 is an equivalent diagram of a conventional series chopper modulation/demodulation chopper clamp.
Fig. 6 is a schematic circuit diagram of embodiment 2.
Fig. 7 is another circuit schematic of embodiment 2.
Fig. 8 is a schematic circuit diagram of embodiment 3.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1
As shown in fig. 6, the balanced differential chopper circuit used in the isolation amplifier includes a chopper circuit, and a differential chopper circuit having a differential structure with the chopper circuit is connected to a ground terminal of a chopper tube of the chopper circuit.
Specifically, the specific implementation circuit and principle of the scheme are still explained by using an N-channel field effect transistor. It should be noted that the chopper tube that can be used for this purpose according to the principles of the present invention can be of many types, such as: n-channel fets, P-channel fets, etc., those skilled in the art will recognize that other chopper-type circuits are also within the scope of the present disclosure.
Example 2
The parallel chopper circuit has a configuration shown in fig. 2, and includes a first resistor connected between the input signal terminal and the first load connection terminal, and a first chopper connected between the first load connection terminal and the ground terminal. The differential chopper circuit having a differential structure with the parallel chopper circuits is constructed as shown in FIG. 6, and includesA second chopper tube coupled between the ground and the second load connection, and a second resistor coupled between the second load connection and the ground. The first resistor and the second resistor have the same resistance, and the first chopper tube and the second chopper tube are the same type or double FET tubes, IGDOHave the same or similar temperature coefficients. The ground terminal of the second resistor may also be connected to the cathode of the input signal terminal as shown in fig. 7. The load is connected between the first load connection terminal and the second load connection terminal, and the grids of the first chopper tube and the second chopper tube are simultaneously connected to a control signal.
The principle that the present solution can solve temperature drift and spike will now be described in detail with this specific circuit.
By adopting the circuit structure, the DC slowly-changing signal V is inputIAlternating signal V generated by series chopperoCan be expressed as:
due to IGDOThe first resistor and the second resistor have the same or similar temperature coefficients, and the resistance values of the first resistor and the second resistor are equal, the above can be simplified as follows:
therefore, the grid-leakage current I of the FET switch tube during deep pinch-off can be greatly reducedGDOThe resulting effect. Followed by an AC amplifier with differential input, or a coupling transformer with a center tap, IGDOThe influence of (b) can be completely suppressed. Due to Vo1And Vo2The transient spike signals are in a common mode and are effectively suppressed after entering a differential alternating current amplifier or a transformer with differential mode input. The RC absorption network is not needed, and the amplitude-frequency characteristic can be greatly improved.
Example 3
The series-parallel chopper circuit adopts the structure shown in fig. 3, and comprises a third resistor, a third chopper tube, a fourth resistor and a fourth chopper tube, wherein the third resistor, the third chopper tube and the fourth resistor are sequentially connected between the anode of the input signal end and the first load connecting end; the differential chopper circuit having a differential structure with the series-parallel chopper circuits is configured as shown in fig. 8, and includes a fifth resistor, a fifth chopper tube, a sixth resistor, and a sixth chopper tube connected between the ground terminal and the second load connection terminal in this order, the third resistor and the fifth resistor have the same resistance value, and the fourth resistor and the sixth resistor have the same resistance value. The load is connected between the first load connecting end and the second load connecting end, and the grids of the third chopper tube and the fifth chopper tube are simultaneously connected to a control signal; the grid electrodes of the fourth chopper tube and the sixth chopper tube are simultaneously connected to a control signal. The principle of solving the temperature drift and the spike is the same as in embodiment 2.
In the series chopper circuit, the equivalent load R is setLThe chopper tube is connected in series, and a differential structure cannot be formed.
Example 4
An isolation amplifier comprises any one of the differential chopper circuits in the above embodiments and an isolation amplifier connected to an output terminal of the differential chopper circuit, the isolation amplifier being an ac amplifier having a differential input or a coupling transformer with a center tap.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (2)
1. A balanced differential chopper circuit is used in an isolation amplifier and comprises a chopper circuit and is characterized in that a differential chopper circuit which forms a differential structure with the chopper circuit is connected to a chopper tube of the chopper circuit; the chopper circuit is a series-parallel chopper circuit,
the series-parallel chopper circuit comprises a third resistor, a third chopper tube, a fourth resistor and a fourth chopper tube, wherein the third resistor, the third chopper tube and the fourth resistor are sequentially connected between the anode of the input signal end and the first load connecting end; the differential chopper circuit comprises a fifth resistor, a fifth chopper tube, a sixth resistor and a sixth chopper tube, wherein the fifth resistor, the fifth chopper tube and the sixth resistor are sequentially connected between a cathode of the input signal end and the second load connecting end, the sixth chopper tube is connected between the ground end and the second load connecting end, the third resistor and the fifth resistor have the same resistance value, and the fourth resistor and the sixth resistor have the same resistance value;
the grid electrodes of the third chopper tube and the fifth chopper tube are connected with the same control signal; one of the source and the drain of the third chopper is connected with a third resistor, and the other is connected with a fourth resistor; one of a source and a drain of the fifth chopper is connected with a fifth resistor, and the other is connected with a sixth resistor;
the grid electrodes of the fourth chopper tube and the sixth chopper tube are connected with the same control signal; one of the source and the drain of the fourth chopper tube is connected with the ground end, and the other one of the source and the drain of the fourth chopper tube is connected with the first load connecting end; one of the source and the drain of the sixth chopper tube is connected to the ground terminal, and the other is connected to the second load connection terminal.
2. An isolation amplifier comprising the differential chopper circuit of claim 1 followed by an isolation amplifier, the isolation amplifier being an ac amplifier with differential inputs or a center tapped coupling transformer.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201710420110.7A CN107241017B (en) | 2017-06-06 | 2017-06-06 | Balanced differential chopper circuit and isolation amplifier based on same |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201710420110.7A CN107241017B (en) | 2017-06-06 | 2017-06-06 | Balanced differential chopper circuit and isolation amplifier based on same |
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| CN107241017A CN107241017A (en) | 2017-10-10 |
| CN107241017B true CN107241017B (en) | 2020-08-04 |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN85103441A (en) * | 1985-04-02 | 1986-10-01 | 山东大学 | Chopper in the high-sensitive DC amplifier |
| GB0522477D0 (en) * | 2005-11-03 | 2005-12-14 | Analog Devices Inc | Modulator |
| CN101867365B (en) * | 2010-04-28 | 2012-01-11 | 广州金升阳科技有限公司 | Circuit for converting direct-current positive and negative bipolar signal into unipolar signal through isolation |
| CN101841308A (en) * | 2010-05-24 | 2010-09-22 | 无锡汉咏微电子有限公司 | Structure of high performance operational amplifier |
| US8704583B2 (en) * | 2012-02-17 | 2014-04-22 | International Business Machines Corporation | Capacitive level-shifting circuits and methods for adding DC offsets to output of current-integrating amplifier |
| US8698545B2 (en) * | 2012-04-03 | 2014-04-15 | Texas Instruments Incorporated | Analog multiplier and method for current shunt power measurements |
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