CN112054773A - Amplifying circuit, power analyzer and measuring device - Google Patents

Abstract

The application discloses an amplifying circuit, a power analyzer and a measuring device. The amplifying circuit comprises an operational amplifier, a voltage division network and a feedback network. The operational amplifier comprises a non-inverting input node, an inverting input node and an output node, wherein the non-inverting input node is coupled to a reference voltage; a voltage divider network coupled between an input signal and an inverting input node, the voltage divider network including a receiving node for receiving the input signal, an intermediate node coupled to the inverting input node, a first input resistor, a first input capacitor, and a second input capacitor coupled in series between the intermediate node and a reference voltage; a feedback network is coupled between the inverting input node and the output node.

Description

Amplifier circuits, power analyzers and measurement devices

technical field

The present application relates to electronic circuits, and more particularly, to an amplifier circuit and a power analyzer and measurement device including the amplifier circuit.

Background technique

Power analyzers can be used to measure power parameters of power conversion devices such as motors, frequency converters, and transformers, such as active power, reactive power, or apparent power. A power analyzer usually includes an input stage circuit to convert the high voltage signal of the device under test into a lower voltage signal, which is then input to the analysis circuit for analysis of the low voltage signal. The structure of this input stage circuit can significantly affect the performance of the power analyzer.

SUMMARY OF THE INVENTION

One of the objectives of the present application is to provide an amplifier circuit with a simple structure.

According to one aspect of the present application, an amplifying circuit is provided, the amplifying circuit includes an operational amplifier, the operational amplifier includes a non-inverting input node, an inverting input node and an output node, the non-inverting input node is coupled to a reference voltage ; a voltage dividing network, the voltage dividing network is coupled between the input signal and the inverting input node, the voltage dividing network includes: a receiving node, the receiving node is used for receiving the input signal; an intermediate node, the an intermediate node coupled to the inverting input node; a first input resistor and a first input capacitor coupled in parallel between the receive node and the intermediate node ; and a second input capacitor coupled between the intermediate node and the reference voltage; and a feedback network coupled between the inverting input node and the output node between.

In some embodiments, the feedback network includes one or more feedback branches, each of the feedback branches being coupled between the inverting input node and the output node.

In some embodiments, the feedback network includes at least one feedback branch including a feedback resistor and a feedback capacitor coupled in parallel with each other.

In some embodiments, the at least one feedback branch further includes a switch in series with the parallel coupled feedback resistor and feedback capacitor.

In some embodiments, the feedback network includes at least one feedback branch including a switch.

In some embodiments, the voltage divider network further includes a second input resistor coupled between the intermediate node and the inverting input node.

In some embodiments, the product of the capacitance value of the first input capacitor and the resistance value of the first input resistor is equal to the difference between the capacitance value of the second input capacitor and the resistance value of the second input resistor product.

In some embodiments, the resistance value of the second input resistor is less than 10% of the resistance value of the first input resistor.

According to another aspect of the present application, there is also provided a power analyzer, the power analyzer comprising the amplification circuit described in the foregoing aspect.

According to another aspect of the present application, there is also provided a measuring device, the measuring device comprising the amplifying circuit as described in the previous aspect.

The above is an overview of the application, and there may be cases of simplification, generalization and omission of details, so those skilled in the art should realize that this part is only illustrative, and is not intended to limit the scope of the application in any way. This Summary section is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

Description of drawings

The above and other features of the present disclosure will be more fully understood by those skilled in the art from the following detailed description taken in conjunction with the accompanying drawings and the appended claims. It is to be understood that these drawings and detailed description depict only several exemplary embodiments of the present disclosure and should not be considered as limiting the scope of the present disclosure. The contents of the present application will be explained more clearly and in detail by referring to the accompanying drawings.

FIG. 1 shows a circuit structure diagram of an amplifying circuit 100 according to an embodiment of the present application.

Detailed ways

In the following detailed description, reference is made to the accompanying drawings which form a part of this specification. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not intended to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter of the present application. It will be appreciated that various configurations, substitutions, combinations, designs of various configurations may be made to the various aspects of the content of the present application generally described in the present application and illustrated in the accompanying drawings, all of which expressly constitute the subject matter of the present application. part.

Referring to FIG. 1 , FIG. 1 schematically shows a circuit structure diagram of an amplifying circuit 100 according to an embodiment of the present application.

As shown in FIG. 1 , the amplifier circuit 100 includes an operational amplifier 102 , a voltage divider network 104 and a feedback network 106 . The operational amplifier 102 includes a non-inverting input node (+), an inverting input node (-) and an output node. In some embodiments, the operational amplifier 102 may be a bipolar junction transistor-based operational amplifier, a field-effect transistor-based operational amplifier, or an operational amplifier implemented based on other suitable devices.

The voltage divider network 104 is coupled between the input signal _Vin and the inverting input node of the operational amplifier 102 for sampling the input signal _Vin . The voltage dividing network 104 can divide the input signal _Vin with a voltage dividing coefficient corresponding to its circuit structure, and generate a sampling signal V _s whose amplitude is smaller than that of the input signal _Vin .

The feedback network 106 is coupled between the inverting input node and the output node of the operational amplifier 102, which together with the voltage divider network 104 enables the operational amplifier 102 to be configured as an inverting amplifier circuit. Compared with the non-inverting amplifier circuit, the inverting amplifier circuit can easily achieve a circuit amplification gain of less than 1, and it is not necessary to add a switch or relay with a higher withstand voltage in the voltage divider network 104 in order to switch the amplification gain of the circuit. , which makes the structure of the amplifying circuit 100 simple and the volume small. For power analyzers or similar electrical measurement devices, the smaller circuit amplification gain of the inverting amplifier circuit can reduce a larger amplitude input voltage (eg, 220V AC voltage) to an amplitude range suitable for electronic measurement devices ( For example, less than or equal to 12V, or less than or equal to 5V); in addition, when the inverting amplifier circuit switches the amplification gain of this small circuit, only a small low-voltage switch is required; therefore, the inverting amplifier circuit structure is adopted. Operational amplifiers are particularly suitable for portable electronic measurement devices. In addition, the smaller circuit amplification gain is also beneficial to realize the wide bandwidth output.

In some embodiments, the feedback network 106 may include one or more feedback branches, and each feedback branch is individually coupled between the inverting input node and the output node. When the feedback network 106 includes multiple feedback branches, the multiple feedback branches are connected in parallel with each other. These feedback branches may have the same or different feedback coefficients. Optionally, each feedback branch may be coupled with a switch for controlling closing or opening of the feedback branch. In this way, by controlling the closed or open state of the switch of each feedback branch, the circuit gain of the amplifier circuit 100 can be adjusted to adapt to different amplitudes of the input signal V _in . In some embodiments, each feedback branch can include a feedback resistor and a feedback capacitor coupled in parallel with each other, wherein the feedback resistor can be used to determine the feedback gain of the feedback branch, and the feedback capacitor can be used to: low pass filtering to filter out high frequency noise that may affect the measurement; to ensure the stability of the amplifier circuit; and to ensure a flat frequency response characteristic of the amplifier circuit in conjunction with a second input capacitor C _in2 , which will be described in detail below. In some embodiments, the feedback capacitor may have a smaller capacitance value, such as 1 picofarad to 200 picofarads, or other suitable capacitance values. In some embodiments, the resistance value of the feedback resistor may be 100 ohms to 500 kiloohms, or other suitable resistance values.

Specifically, as shown in FIG. 1 , the voltage dividing network 104 includes a receiving node IN, an intermediate node IMN, a first input resistor R _in1 , a first input capacitor C _in1 and a second input capacitor C _in2 . The receiving node IN is used to receive the input signal V _in ; the intermediate node IMN is coupled to the inverting input node of the operational amplifier 102 ; the first input resistor R _in1 and the first input capacitor C _in1 are coupled in parallel to the receiving node IN and between the intermediate nodes IMN; the second input capacitor C _in1 is coupled in series between the intermediate node IMN and the reference voltage V _ref ; the feedback network 106 is coupled between the inverting input node and the output node OUT of the operational amplifier 102 . As shown in FIG. 1 , the feedback network 106 includes one or more feedback branches, each of which includes a feedback resistor R _f and a feedback capacitor C _f coupled in parallel with each other, and a switch S for controlling the feedback branch closing or opening of the circuit. In some embodiments, the non-inverting input node is coupled to the reference voltage _Vref . The amplifying circuit shown in FIG. 1 can generate an output signal V _out in the form of a voltage based on the voltage of the input signal V _in , wherein the second input capacitor C _in2 plays a major role in obtaining a flat frequency response characteristic, and its capacitance value is usually higher than large (eg, several thousand picofarads or other suitable capacitance). It can be seen that the output terminal of the operational amplifier 102 does not directly drive the second input capacitor C _in2 , which can improve the stability of the amplifier circuit 100 itself. In addition, the amplifying circuit 100 only has a single-stage amplification, which is not only beneficial to reduce the circuit volume, but also can effectively avoid the noise introduced into the circuit by the multi-stage amplification.

For the input signal V _{in in} AC form, the voltage dividing coefficient of the voltage dividing network 104 depends on the ratio of the capacitance values of the first input capacitor C _in1 and the second input capacitor C _in2 , specifically, the sampled signal V generated at the intermediate node IMN _s can be represented by the following equation (1):

In the embodiment shown in FIG. 1 , the voltage divider network 104 further includes a second input resistor R _in2 coupled _between the intermediate node IMN and the inverting input node of the operational amplifier 102 . Due to the virtual short characteristic of the operational amplifier, the non-inverting input node and the inverting input node can be considered to have the same potential, that is, the potential of the non-inverting input node is equal to the reference voltage V _ref . Based on this, when the reference voltage _Vref is assumed to be zero, the circuit transfer function of the amplifier circuit 100 is represented by the following equation (2) (without considering the value of the feedback capacitance in the feedback network):

Wherein, R _fi represents the resistance value of the feedback resistor coupled in the selected feedback branch, and R _fi may be one of the selected R _f1 to R _fn , or these feedback resistors R, depending on the operation of the specific circuit. Parallel combination of _f1 to R _fn (multiple feedback branches are selectively closed).

It can be seen that for the input signal in the form of high frequency AC, the circuit amplification gain of the amplifier circuit 100 is affected by the resistance value of the second input resistor R _in2 , and the larger the resistance value is, the smaller the circuit amplification gain is. In some embodiments, the resistance value of the second input resistor R _in2 may be set to a small value, eg, the resistance value of the second input resistor R _in2 is less than 10% of the resistance value of the first input resistor R _in1 . In some embodiments, the first input resistor R _in1 may have a resistance value of 200 kohms to 100 megohms (eg, 2 megohms), and the second input resistor R _in2 may have a resistance value of 1 kohms to 100 megohms 500k ohms (eg, 10k ohms), or other suitable resistance values.

Since the inverting input node is considered to be coupled to the reference voltage V _ref , also assuming that V _ref is zero, the input impedance R _in of the amplifier circuit 100 is represented by the following equation (3):

因此放大电路100的增益是平坦的。In some embodiments, the product of the capacitance value of the first input capacitor C _in1 and the resistance value of the first input resistor R _in1 is equal to the capacitance value of the second input capacitor C _in2 and the resistance of the second input resistor R _in2 This can reduce the number of poles of the amplifier circuit 100. From equation (3), it can be known that the change of the input impedance R _in with frequency is flat, that is, the frequency response curve of the amplifier circuit 100 is flatter. In addition, when the product of the capacitance value of the first input capacitor C _in1 and the resistance value of the first input resistor R _in1 is equal to the product of the capacitance value of the second input capacitor C _in2 and the resistance value of the second input resistor R _in2 , it can be known from the above equation (2) that the gain H of the amplifier circuit 100 is equal to

Therefore, the gain of the amplifier circuit 100 is flat.

In some embodiments, corresponding to the resistance values of the first input resistor R _in1 and the second input resistor R _in2 above, the capacitance value of the first input capacitor C _in1 may be 0.5 picofarads to 250 picofarads (eg, 5 picofarads), and the capacitance value of the second input resistor C _in2 may be 100 picofarads to 50 kpicofarads (eg, 1000 picofarads), or other suitable capacitance values.

In some embodiments, the amplification circuit shown in the embodiments of the present application may be used in a power analyzer or other measurement device. In particular, the amplifying circuit shown in the embodiments of the present application can be used in a portable power analyzer or measuring device, for example, as an input stage circuit of the portable power analyzer or measuring device to sample voltage. It can be understood that, for the power analyzer, in addition to the amplifying circuit for sampling voltage shown in FIG. 1, it may also include a current sampling circuit for sampling current, and the current sampling circuit may be, for example, an inductance coil or other similar current sampling or sensing circuit. By calculating the sampling current and sampling voltage, the power analyzer can obtain the power of the device under test.

Other modifications to the disclosed embodiments can be understood and effected by those of ordinary skill in the art from a study of the specification, disclosure and drawings, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps and the word "a", "an" does not exclude plurals. In a practical application of the present application, one component may perform the functions of several technical features recited in the claims. Any reference signs in the claims shall not be construed as limiting the scope.

Claims (10)

1. An amplifying circuit, characterized in that the amplifying circuit comprises: an operational amplifier including a non-inverting input node, an inverting input node and an output node, the non-inverting input node being coupled to a reference voltage; a voltage divider network coupled between the input signal and the inverting input node, the voltage divider network comprising: a receiving node, the receiving node is configured to receive the input signal; an intermediate node coupled to the inverting input node; a first input resistor and a first input capacitor coupled in parallel between the receive node and the intermediate node; and a second input capacitor coupled between the intermediate node and the reference voltage; and a feedback network coupled between the inverting input node and the output node. 2 . The amplifier circuit according to claim 1 , wherein the feedback network comprises one or more feedback branches, and each of the feedback branches is coupled to the inverting input node and the output node. 3 . between. 3. The amplifier circuit of claim 1, wherein the feedback network comprises at least one feedback branch, the at least one feedback branch comprising a feedback resistor and a feedback capacitor coupled in parallel with each other. 4. The amplifier circuit of claim 3, wherein the at least one feedback branch further comprises a switch in series with the parallel coupled feedback resistor and feedback capacitor. 5. The amplifier circuit of claim 1, wherein the feedback network comprises at least one feedback branch, and the at least one feedback branch comprises a switch. 6. The amplifying circuit according to claim 1, wherein the voltage dividing network further comprises: A second input resistor coupled between the intermediate node and the inverting input node. 7. The amplifier circuit according to claim 6, wherein the product of the capacitance value of the first input capacitor and the resistance value of the first input resistor is equal to the capacitance value of the second input capacitor and the the product of the resistance values of the second input resistors. 8. The amplifier circuit according to claim 6, wherein the resistance value of the second input resistor is less than 10% of the resistance value of the first input resistor. 9 . A power analyzer, characterized in that, the power analyzer comprises the amplification circuit according to any one of claims 1 to 8 . 10. A measuring device, characterized in that, the measuring device comprises the amplifying circuit according to any one of claims 1 to 8.

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