TWI535192B - Ac coupled amplifier circuit - Google Patents

Description

AC coupled amplifier circuit

The present invention relates to an AC coupled amplifier circuit, and more particularly to an AC coupled amplifier circuit that reduces the time to stabilize an AC signal.

The AC coupling circuit is used to transmit the output AC signal of the previous stage circuit to the next stage circuit, so it is widely used in oscilloscopes, power supplies, and electronic test instruments. In general, the main purpose of the AC coupling circuit is to couple AC and isolate DC. Common AC coupling circuits include a resistor-capacitor coupling circuit (RC coupling circuit), a direct coupling circuit, a transformer coupling circuit, and the like. The advantages of the conventional resistor-capacitor coupling circuit are low cost and small size. However, the product of the resistor and the capacitor in the conventional RC-coupled circuit is usually set so that the cut-off frequency of the coupled signal is low, so that the higher-frequency signal is not attenuated. However, a larger capacitor causes the resistor-capacitor coupling circuit to take longer to stabilize the AC signal when coupled.

Please refer to FIG. 1. FIG. 1 is a waveform diagram showing the relationship between an output signal and an input signal generated by a conventional AC coupling circuit. As shown in Figure 1, when the voltage of the DC signal in the input signal is 3 volts, The peak-to-peak voltage of the incoming signal of the input signal is 2 volts, and the frequency of the sine wave is 1 kilohertz (KHz). The output signal (ie, the AC signal) generated by the conventional AC-coupled amplifying circuit requires an AC signal stabilization time of at least 500 milliseconds (ms). When a conventional AC-coupled amplifying circuit is applied to an oscilloscope, a power supply, and an electronic test instrument, such a situation may cause a delay in outputting an unstable AC signal, and an increase in test time.

Therefore, in order to solve the above problems, the present invention provides an AC coupled amplifier circuit for reducing the stabilization time of an AC signal.

One aspect of the present invention is directed to an AC coupled amplifier circuit. The AC coupled amplifier circuit includes a first capacitor, an amplifier, an input resistor, and an acceleration resistor. The first capacitor is configured to receive the first signal and output an alternating signal in the first signal. The amplifier is used to amplify the alternating signal to generate a second signal. The input resistor is electrically coupled to the first capacitor. The acceleration resistor is electrically coupled to the first capacitor through a switch, wherein the resistance value of the acceleration resistor is much smaller than the resistance value of the input resistor. During the initial period in which the first capacitor receives the first signal, the switch is turned on, and after the initial period, the switch is turned off.

According to an embodiment of the invention, the AC coupled amplifier circuit further includes a zero point detecting circuit. The zero detection circuit is configured to generate a control signal according to the voltage of the second signal to open the switch.

According to an embodiment of the invention, the zero point detecting circuit is configured to selectively detect a voltage when the phase of the second signal is 0 degrees or 180 degrees, and selectively select a phase of the second signal Generated at 0 or 180 degrees The control signal.

According to an embodiment of the invention, the zero point detection circuit includes a comparator. The comparator is configured to compare the voltage of the second signal with a reference voltage to generate the control signal.

According to an embodiment of the invention, the AC coupled amplifier circuit further includes a coupling circuit. The coupling circuit is electrically coupled between the amplifier and the zero point detecting circuit. The coupling circuit is configured to capture the second signal to the zero point detecting circuit during the initial period.

According to an embodiment of the invention, the coupling circuit includes a second capacitor and a coupling resistor. The second capacitor is electrically coupled between the amplifier and the zero point detecting circuit, wherein a capacitance value of the second capacitor is much smaller than a capacitance value of the first capacitor. The coupling resistor is electrically coupled to the second capacitor. The resistance of the coupling resistor is approximately equal to the resistance of the input resistor.

According to an embodiment of the invention, during the initial period, the direct current signal in the first signal charges the first capacitor through the input resistance and the acceleration resistor connected in parallel.

Another aspect of the present invention is directed to an AC coupled amplifier circuit. The AC coupled amplifier circuit includes a first capacitor, an amplifier, an input resistor, and an acceleration resistor. The first capacitor includes a first end and a second end. The first end of the first capacitor is configured to receive the first signal. The amplifier contains an input and an output. The input end of the amplifier is electrically coupled to the second end of the first capacitor. The output of the amplifier is used to output an AC signal in the amplified input signal. The input resistor includes a first end and a second end. The first end of the input resistor is electrically coupled to the second end of the first capacitor. The second end of the input resistor is electrically coupled to the ground. Accelerating electricity The resistor includes a first end and a second end. The first end of the acceleration resistor is electrically coupled to the second end of the first capacitor through a switch. The second end of the acceleration resistor is electrically coupled to the ground, wherein the resistance of the acceleration resistor is much smaller than the resistance of the input resistor. When the first capacitor receives the first signal, the switch is turned on, and after the initial period, the switch is turned off.

According to an embodiment of the invention, the AC coupled amplifier circuit further includes a comparator. The comparator includes a first input, a second input, and an output. The first input of the comparator is electrically coupled to the output of the amplifier. The second input of the comparator is for receiving a reference voltage. The output of the comparator is used to output a control signal to open the switch.

According to an embodiment of the invention, the AC coupled amplifier circuit further includes a second capacitor and a coupling resistor. The second capacitor includes a first end and a second end. The first end of the second capacitor is electrically coupled to the output end of the amplifier. The second end of the second capacitor is electrically coupled to the first input end of the comparator, wherein a capacitance value of the second capacitor is much smaller than a capacitance value of the first capacitor. The coupling resistor includes a first end and a second end. The first end of the coupling resistor is electrically coupled to the second end of the second capacitor. The second end of the coupling resistor is electrically coupled to the ground, wherein the resistance of the coupling resistor is approximately equal to the resistance of the input resistor.

In summary, when the AC-coupled amplifying circuit starts to receive the first signal, that is, when the first signal is received through the first capacitor, the switch is turned on, so that the DC signal in the first signal passes through the parallel input resistance and the resistance value is far. An acceleration resistor that is smaller than the input resistor quickly charges the first capacitor to quickly filter out the DC signal and maintain the switch on during the initial period. then, Through the zero detection circuit and the coupling circuit, the zero position of the second signal can be quickly detected, and after detecting the zero position of the second signal, the switch is opened, so that the amplifier reconnects the original input impedance and restores the original coupled signal. Size and reduce the time to stabilize the second signal. When the AC-coupled amplifying circuit is applied to an oscilloscope, the time of the signal test can be further reduced, especially for the high-voltage chopping measurement, which has a significant advantage in the test speed.

200‧‧‧AC coupled amplifier circuit

210‧‧‧ Analog/Digital Converter

220‧‧‧Input resistance

230‧‧‧Acceleration resistance

240‧‧‧Amplifier

250‧‧‧ Zero detection circuit

251‧‧‧ Comparator

260‧‧‧coupled circuit

261‧‧‧Coupling resistor

270‧‧‧ first buffer

280‧‧‧second buffer

CP1‧‧‧first capacitor

CP2‧‧‧second capacitor

SIG1‧‧‧ first signal

SIG2‧‧‧ second signal

CTL‧‧‧ control signal

GND‧‧‧ ground terminal

VREF‧‧‧reference voltage

SW‧‧ switch

The above and other objects, features, advantages and embodiments of the present invention will become more <RTIgt; <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; FIG. 2 is a schematic diagram of an AC-coupled amplifying circuit according to an embodiment of the invention; and FIG. 3 is a schematic diagram of an AC-coupled amplifying circuit according to an embodiment of the invention. A waveform diagram of the relationship between the output signal and the input signal.

The following embodiments are described in detail with reference to the accompanying drawings, but the embodiments are not intended to limit the scope of the invention, and the description of structural control is not intended to limit the order of execution, any The structure, which produces equal devices, is within the scope of the present invention. In addition, the drawings are for illustrative purposes only and are not based on the original size. Figure. For ease of understanding, the same elements in the following description will be denoted by the same reference numerals.

As used herein, "about", "about" or "substantially" generally means that the error or range of the index value is within 20%, preferably within 10%, and more preferably It is within 5 percent. In the text, unless otherwise stated, the numerical values referred to are regarded as approximations, such as an error or range indicated by "about", "about" or "substantial", or other approximations.

The terms "first", "second", etc., as used herein, are not intended to refer to the order or the order, and are not intended to limit the invention, only to distinguish the elements described in the same technical terms. Or control only.

In addition, the term "coupled" or "connected" as used herein may mean that two or more elements are in direct physical or electrical contact with each other, or indirectly in physical or electrical contact with each other, or Multiple components control or act on each other.

Referring to FIG. 2, FIG. 2 is a schematic diagram of an AC-coupling amplifying circuit 200 according to an embodiment of the invention. The AC-coupled amplifying circuit 200 can receive the first signal SIG1 outputted by the first-stage amplifier (not shown), filter the DC signal in the first signal SIG1, and amplify the AC signal in the first signal SIG1. The second signal SIG2 is generated, and then the second signal SIG2 is output to the next-stage amplifying device (not shown). In other words, the AC-coupled amplifying circuit 200 can couple and amplify the AC component in the signal output from the previous stage amplifier to the next stage amplifier. In this embodiment, the AC coupling amplifying circuit 200 transmits the second signal. The SIG2 is output to the analog/digital converter 210, but the embodiment is not limited thereto.

As shown in FIG. 2, the AC-coupled amplifier circuit 200 includes a first capacitor CP1, an input resistor 220, an acceleration resistor 230, and an amplifier 240. The first capacitor CP1 includes a first end and a second end. The first end of the first capacitor CP1 is configured to receive the first signal SIG1. Input resistor 220 includes a first end and a second end. The first end of the input resistor 220 is electrically coupled to the second end of the first capacitor CP1. The second end of the input resistor 220 is electrically coupled to the ground GND. The acceleration resistor 230 includes a first end and a second end. The first end of the acceleration resistor 230 is electrically coupled to the second end of the first capacitor CP1 through the switch SW. The second end of the acceleration resistor 230 is electrically coupled to the ground GND. Amplifier 240 includes an input and an output. The input end of the amplifier 240 is electrically coupled to the second end of the first capacitor CP1. The output of the amplifier 240 is used to output an AC signal (ie, the second signal SIG2) of the amplified input signal to the analog/digital converter 210.

In the present embodiment, the resistance value of the acceleration resistor 230 is much smaller than the resistance value of the input resistor 220. In one embodiment, the resistance value of the acceleration resistor 230 is approximately one thousandth of the resistance value of the input resistor 220, but the invention is not limited thereto.

In an operation, when the AC-coupled amplifying circuit 200 receives the first signal SIG1 output from the upper-stage amplifier (not shown) (that is, receives the first signal SIG1 through the first capacitor CP1), the switch SW1 is Turn on. At this time, the first capacitor CP1 is electrically coupled to the parallel input resistor 220 and the acceleration resistor 230. At this time, the DC signal in the first signal SIG1 passes through the parallel input resistor 220 and the acceleration resistor 230 to the first capacitor CP1. Charge it. Since the resistance value of the acceleration resistor 230 is much smaller than the resistance value of the input resistor 220, the resistance value after the parallel connection is approximately equal to the resistance value of the acceleration resistor 230. In other words, at this time, the first capacitor CP1 is electrically coupled to a smaller resistance than the originally matched input resistor 220, and thus the charging speed is much faster than the originally matched impedance.

Therefore, the DC signal in the first signal SIG1 can be quickly filtered out through the first capacitor CP1 and the parallel input resistor 220 and the acceleration resistor 230. In one embodiment, if the resistance of the acceleration resistor 230 is approximately one thousandth of the resistance of the input resistor 220, the speed at which the DC signal is filtered can be thousands of times faster than the originally matched impedance.

In the above embodiment, the AC-coupled amplifying circuit 200 can quickly filter out the DC signal in the first signal SIG1 through the parallel acceleration resistor 230. However, the parallel acceleration resistor 230 causes the input impedance of the original circuit to become smaller, so that the amplitude of the alternating current signal supplied to the first signal SIG1 of the amplifier 240 becomes smaller, thereby causing it to be supplied to the next stage circuit (for example, the analog/digital converter 210). The amplitude of the signal is not the size of the original circuit. Therefore, in order for the signal output by the amplifier 240 (eg, the second signal SIG2) to be the original signal, the input impedance coupled to the first capacitor CP1 must be changed from the parallel input resistor 220 and the acceleration resistor 230 back to the input resistor 220. That is, the switch SW is turned off. However, at the moment when the switch SW is turned off, the AC signal in the first signal SIG1 still has a transient voltage change.

Further, if the AC signal in the first signal SIG1 is not operated at the zero position at the moment when the switch SW is turned off (that is, the phase of the AC signal is 0 or 180 degrees), the AC signal will be generated. Start point If the voltage level is not zero, it will take some time for the AC signal to correct the offset operating point to the correct zero position.

In addition, in addition to the transient response of the AC signal itself, when the AC signal is amplified by the amplifier 240, the zero position of the AC signal is also offset. In other words, the position of the zero point of the second signal SIG2 (and the alternating current signal) amplified by the amplifier 240 is usually not at the level of zero voltage, that is, the zero position of the second signal SIG2 usually has an offset voltage.

Therefore, in order to make the zero position of the AC signal received by the next stage amplifier (for example, the analog/digital converter 210) normal, the AC coupled amplifier circuit 200 further includes a zero point detecting circuit 250. In an embodiment, the zero point detecting circuit 250 is configured to generate the control signal CTL according to the voltage of the second signal SIG2 to turn off the switch SW. Further, the zero detection circuit 250 can be used to selectively detect the voltage when the phase of the second signal SIG2 is 0 degrees or 180 degrees (that is, the zero position of the second signal SIG2), and is selective to the second signal. When the phase of SIG2 is 0 degrees or 180 degrees, the control signal CTL is generated to open the switch SW. In other words, when the phase of the second signal SIG2 is 0 degrees or 180 degrees, the switch SW is turned off, so that the amplifier 240 is electrically coupled to the first capacitor CP1 and the input resistor 220. Therefore, the amplifier 240 can operate at the original input impedance (ie, the input resistor 220), and the zero position of the amplified second signal SIG2 does not shift, thereby further eliminating the offset of the AC signal. The time is such that the AC coupled amplifier circuit 200 uses less time to stabilize the input of the AC signal.

In an embodiment, the zero detection circuit 250 includes a comparator 251. The comparator 251 includes a first input, a second input, and an output. The first input of the comparator 251 is electrically coupled to the output of the amplifier 240. The second input of the comparator 251 is for receiving the reference voltage VREF. The output of the comparator 251 is used to output a control signal CTL to turn off the switch SW.

In an operation, the comparator 251 is configured to compare the voltage of the second signal SIG2 with the reference voltage VREF. The magnitude of the reference voltage VREF is approximately equal to the magnitude of the offset voltage produced by amplifier 240. Therefore, when the voltage of the second signal SIG2 is approximately equal to the reference voltage VREF, it represents that the voltage of the second signal SIG2 is approximately equal to the offset voltage, that is, the phase of the second signal SIG2 is 0 degree or 180 degrees. The voltage at the time, that is, the zero position of the second signal SIG2. At this time, the comparator 251 can generate a control signal CTL (for example, a low voltage level signal) to open the switch SW (for example, an N-type metal oxide semiconductor). In this way, through the comparator 251, the zero detection circuit 250 can accurately detect the zero position of the second signal SIG2 (alternating signal). Thereby, the time for the AC-coupled amplifying circuit 200 to stabilize the AC signal of the input signal is less.

In an embodiment, the AC coupled amplifier circuit 200 further includes a coupling circuit 260. The coupling circuit 260 is electrically coupled between the amplifier 240 and the zero detection circuit 250. The coupling circuit 260 is configured to quickly capture the second signal SIG2 to the zero detection circuit 250 during the initial period, so that the zero detection circuit 250 can quickly detect the zero position of the second signal SIG2, thereby reducing the time for stabilizing the second signal SIG2. .

In an embodiment, the coupling circuit 260 includes a second capacitor CP2 and a coupling resistor 261. The second capacitor CP2 includes a first end and a second end. First The first end of the second capacitor CP2 is electrically coupled to the output of the amplifier 240. The second end of the second capacitor CP2 is electrically coupled to the first input end of the comparator 251. The coupling resistor 261 includes a first end and a second end. The first end of the coupling resistor 261 is electrically coupled to the second end of the second capacitor CP2. The second end of the coupling resistor 261 is electrically coupled to the ground GND.

In this embodiment, the capacitance value of the second capacitor CP2 is much smaller than the capacitance value of the first capacitor CP1. In one embodiment, the capacitance of the second capacitor CP2 is approximately one thousandth of the capacitance of the first capacitor CP1, but the invention is not limited thereto. In addition, the resistance value of the coupling resistor 261 is approximately equal to the resistance value of the input resistor 220. Since the zero point detection circuit 250 still needs an input resistance value matched with the amplifier 240 to accurately detect the size of the second signal SIG2. Therefore, in the coupling circuit 260, only the capacitance value of the second capacitor CP2 is adjusted.

Similarly, since the capacitance value of the second capacitor CP2 is much smaller than the capacitance value of the first capacitor CP1, the time for capturing the second signal SIG2 through the second capacitor CP2 and the coupling resistor 261 is also greatly reduced. In an embodiment, if the capacitance of the second capacitor CP2 is about one thousandth of the capacitance of the first capacitor CP1, the speed of the second signal SIG2 is faster than the impedance of the original matching. Times.

In an embodiment, the AC coupled amplifier circuit 200 further includes a first buffer 270 and a second buffer 280. The first buffer 270 includes an input and an output. The input end of the first buffer 270 is electrically coupled to the second end of the first capacitor CP1. The output end of the first buffer 270 is electrically coupled to the input end of the amplifier 240. The first buffer 270 is configured to buffer the alternating signal of the first signal SIG1. The second buffer 280 includes an input and an output. Second buffer The input end of the second capacitor 280 is electrically coupled to the first end of the second capacitor CP2. The second buffer 280 is configured to buffer the second signal SIG2.

According to the embodiment of the present invention, when the AC-coupled amplifier circuit 200 starts to receive the first signal SIG1 (for example, the AC-DC signal transmitted by the amplifier of the previous stage), that is, the first signal SIG1 is received through the first capacitor CP1. When the switch SW7 is turned on, the DC signal in the first signal SIG1 is quickly charged to the first capacitor CP1 through the parallel input resistor 220 and the acceleration resistor 230 whose resistance value is much smaller than the input resistor 220, so as to quickly filter out the DC signal, and The switch SW is kept turned on during the initial period. Then, the zero point detecting circuit 250 and the coupling circuit 260 can quickly detect the zero position of the second signal SIG2 (ie, the alternating current signal) (for example, the position of the alternating current signal is 0 degree or 180 degrees), and is detected. After the zero position of the second signal SIG2 is turned off, the switch SW is turned off (that is, after the initial period), so that the amplifier 240 reconnects the originally matched input impedance (ie, the first capacitor CP1 and the input resistor 220), thereby reducing the stability of the second The time of the signal SIG2. When the AC-coupled amplifying circuit 200 is applied to an oscilloscope, the time of the signal test can be further reduced, especially for the high-voltage chopping measurement, which has a significant advantage in the test speed.

Referring to FIG. 3, FIG. 3 is an output signal (eg, second signal SIG2) generated by the AC-coupled amplifying circuit 200 and an input signal (eg, the first signal SIG1) according to an embodiment of the invention. A waveform diagram of the relationship. In the present embodiment, the magnification of the amplifier 240 is set to be doubled. As shown in Figure 3, when the DC signal in the signal is input The voltage is 3 volts, and the peak-to-peak voltage of the input signal is 2 volts, and the frequency of the sine wave is 1 kilohertz (KHz). The output signal (ie, the AC signal) generated by the AC-coupled amplifying circuit 200 is shortened from the original 500 milliseconds (as shown in FIG. 1) to 50 milliseconds. In other words, through the AC-coupled amplifying circuit 200 disclosed in the present invention, the time for stabilizing the AC signal can be shortened to one tenth of the time required for the stabilization of the conventional coupling circuit. When the DC signal and the AC signal in the input signal are larger, the AC signal stabilization time improved by the AC-coupled amplifying circuit 200 is more obvious.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and the present invention can be modified and modified without departing from the spirit and scope of the present invention. The scope is subject to the definition of the scope of the patent application attached.

200‧‧‧AC coupled amplifier circuit

210‧‧‧ Analog/Digital Converter

220‧‧‧Input resistance

230‧‧‧Acceleration resistance

240‧‧‧Amplifier

250‧‧‧ Zero detection circuit

251‧‧‧ Comparator

260‧‧‧coupled circuit

261‧‧‧Coupling resistor

270‧‧‧ first buffer

280‧‧‧second buffer

CP1‧‧‧first capacitor

CP2‧‧‧second capacitor

SIG1‧‧‧ first signal

SIG2‧‧‧ second signal

CTL‧‧‧ control signal

GND‧‧‧ ground terminal

VREF‧‧‧reference voltage

SW‧‧ switch

Claims (8)

An AC-coupled amplifying circuit includes: a first capacitor for receiving a first signal and outputting an AC signal of the first signal; an amplifier for amplifying the AC signal to generate a second signal; an input The resistor is electrically coupled to the first capacitor; an accelerating resistor is electrically coupled to the first capacitor through a switch, wherein the resistance of the accelerating resistor is much smaller than the resistance of the input resistor; and a zero point detecting circuit And generating a control signal according to the voltage of the second signal to turn off the switch, wherein the switch is turned on during an initial period in which the first capacitor receives the first signal, and after the initial period, the switch is off open. The AC-coupled amplifying circuit of claim 1, wherein the zero-point detecting circuit is configured to selectively detect a voltage when the phase of the second signal is 0 degrees or 180 degrees, and selectively select the second signal. The control signal is generated when the phase is 0 degrees or 180 degrees. The AC-coupled amplifying circuit of claim 1, wherein the zero-point detecting circuit comprises a comparator for comparing the voltage of the second signal with a reference voltage to generate the control signal. The AC-coupled amplifying circuit of claim 1, further comprising a coupling circuit electrically coupled between the amplifier and the zero point detecting circuit, the coupling The circuit is configured to capture the second signal to the zero point detecting circuit during the initial period. The AC-coupled amplifying circuit of claim 4, wherein the coupling circuit comprises: a second capacitor electrically coupled between the amplifier and the zero detecting circuit, wherein a capacitance of the second capacitor is much smaller than the first a capacitance value of a capacitor; and a coupling resistor electrically coupled to the second capacitor, wherein the resistance of the coupling resistor is approximately equal to a resistance value of the input resistor. The AC-coupled amplifying circuit of claim 1, wherein in the initial period, the DC signal in the first signal charges the first capacitor through the input resistor and the acceleration resistor connected in parallel. An AC-coupled amplifying circuit includes: a first capacitor, comprising a first end and a second end, the first end of the first capacitor is configured to receive a first signal; and an amplifier includes an input end and a first The output end of the amplifier is electrically coupled to the second end of the first capacitor, the output end of the amplifier is configured to output an AC signal in the amplified input signal; and an input resistor includes a The first end is electrically coupled to the second end of the first capacitor, and the second end of the input resistor is electrically coupled to a ground end; An acceleration resistor includes a first end and a second end, the first end of the accelerating resistor is electrically coupled to the second end of the first capacitor through a switch, and the second end of the accelerating resistor is electrically The grounding end is coupled to the grounding end, wherein the resistance value of the acceleration resistor is much smaller than the resistance value of the input resistor; and a comparator includes a first input end, a second input end, and an output end, the first of the comparators An input is electrically coupled to the output of the amplifier, the second input of the comparator is configured to receive a reference voltage, and the output of the comparator is configured to output a control signal to turn off the switch, wherein The switch is turned on during an initial period in which the first capacitor receives the first signal, and after the initial period, the switch is turned off. The AC-coupled amplifying circuit of claim 7, further comprising: a second capacitor comprising a first end and a second end, the first end of the second capacitor being electrically coupled to the output of the amplifier The second end of the second capacitor is electrically coupled to the first input end of the comparator, wherein a capacitance value of the second capacitor is much smaller than a capacitance value of the first capacitor; and a coupling resistor includes a first The first end of the coupling resistor is electrically coupled to the second end of the second capacitor, and the second end of the coupling resistor is electrically coupled to the ground end, wherein the coupling resistor The resistance value is approximately equal to the resistance value of the input resistor.