CN103913240A - Current type terahertz pyroelectricity detector reading circuit - Google Patents

Abstract

The invention discloses a readout circuit of a current-type terahertz pyroelectric detector, which belongs to the field of terahertz detection and imaging. The readout circuit includes a current-voltage converter, a 50Hz trap circuit, a first-order low-pass filter amplifier circuit and a potential raising module. Among them, the signal output by the terahertz pyroelectric detector is input into the current-voltage converter, which is used to convert the current signal into a voltage signal; the signal output by the current-voltage converter is input into the 50Hz trap circuit, which is used to eliminate power frequency interference; The signal output by the 50Hz notch circuit is input into the first-order low-pass filter amplifier circuit for further signal amplification; the signal output by the first-order low-pass filter amplifier circuit is then input into the potential raising module, which is used to raise the voltage so that the voltage signal output by the circuit is consistent with the subsequent The voltage required by the terminal digital acquisition circuit matches. The voltage signal output by the readout circuit is pure, and is suitable for collecting and outputting the weak current of the terahertz pyroelectric detector.

Description

A current mode terahertz pyroelectric detector readout circuit

technical field

The invention belongs to the field of terahertz detection and imaging, in particular to a readout circuit of a current-type terahertz pyroelectric detector.

Background technique

Terahertz (THz) wave is an electromagnetic wave with a frequency in the range of 0.1THz to 10THz, and a wavelength in the range of 30μm to 3mm, which is between microwave and infrared, and is a very important band in the electromagnetic spectrum. Compared with electromagnetic waves in other bands, terahertz radiation has unique and excellent properties such as wide frequency bandwidth, narrow pulse width, good coherence, and low energy. Pay attention to. Compared with other types of terahertz detectors, pyroelectric terahertz detectors have the advantages of miniaturization, wide-spectrum detection, low cost, and fast response, and are currently a widely studied THz detection technology. However, compared with pyroelectric detectors used for infrared imaging, the output signal current of terahertz pyroelectric detectors is weaker, often in the order of pA or even sub-pA. Signal flooded. At present, the readout circuits of terahertz pyroelectric detectors can be divided into two categories, namely voltage mode and current mode. Among them, the voltage mode realizes current-voltage conversion by means of a junction field effect transistor (JFET), which has the characteristics of simple structure, but the disadvantage is that its electrical response time is determined by the equivalent capacitance of the pyroelectric chip and the gate resistance, which is generally within 1 second. On the one hand, this makes the response of the detector slower; on the other hand, it is difficult to eliminate low-frequency interference below 1 Hz (such as external random vibration interference). The current mode uses a CMOS operational amplifier to realize current-voltage conversion, and its detector response time is only related to the feedback impedance, and its order of magnitude is generally tens of milliseconds. In addition, the operating frequency of the current mode detector is generally above tens of Hz or even hundreds of Hz (determined by the feedback impedance), so the low frequency interference is greatly reduced.

Current-mode readout circuits have the advantages of fast response time and low-frequency interference, so they have attracted great attention from researchers. However, the output signal current of the terahertz pyroelectric detector is very weak, and the readout circuit still needs to be carefully designed.

Contents of the invention

The present invention studies and designs a current-type terahertz pyroelectric detector readout circuit to eliminate power frequency interference and other unwanted signal interference, thereby outputting a pure signal voltage, and controlling it through a potential raising module containing a sliding rheostat The boosting multiple of the output voltage makes the voltage signal output by the circuit match the voltage required by the back-end digital acquisition circuit.

Technical scheme of the present invention is as follows:

A current-type terahertz pyroelectric detector readout circuit, including a current-voltage converter 1, a 50Hz trap circuit 2, a first-order low-pass filter amplifier circuit 3 and a potential raising module 4, the terahertz pyroelectric detector The output signal is input into the current-voltage converter 1, which is used to convert the current signal into a voltage signal, and the voltage signal output by the current-voltage converter is input into the 50Hz trap circuit 2, which is used to eliminate power frequency interference, and the output of the 50Hz trap circuit The signal is input to the first-order low-pass filter amplifier circuit 3 for further amplifying the signal, and the signal output by the first-order low-pass filter amplifier circuit is then input to the potential raising module 4 for raising the voltage so that the voltage signal output by the circuit is compatible with the back-end digital acquisition circuit match the required voltage. Among them, the current-voltage converter 1 includes a signal output terminal of the terahertz pyroelectric detector, an operational amplifier and a feedback circuit, the signal output terminal of the terahertz pyroelectric detector is connected to the inverting input terminal of the operational amplifier, and the terahertz pyroelectric detector signal output terminal is connected to the inverting input terminal of the operational amplifier. The ground terminal of the electrical detector is connected to the non-inverting input terminal of the operational amplifier, the feedback circuit is connected between the inverting input terminal of the operational amplifier and the output terminal of the operational amplifier, and the feedback circuit is connected in parallel by a feedback resistor and a feedback capacitor.

Further, a current-limiting resistor is connected in series between the connection between the feedback circuit and the output terminal of the terahertz pyroelectric detector in the current-voltage converter and the inverting input terminal of the operational amplifier.

Furthermore, in the first-order low-pass filter amplifying circuit, the feedback resistor is composed of a fixed resistor and a sliding rheostat connected in series.

Furthermore, in the potential raising module, a sliding rheostat connected in series with a fixed resistor is used in the voltage divider circuit connected to the non-inverting input of the operational amplifier to control the raising multiple of the voltage signal.

Among them, the operational amplifier in the current-voltage converter 1 is the AD8627 operational amplifier; the 50Hz trap circuit 2 is based on the F42N50 module; the cut-off frequency of the first-order low-pass filter amplifier circuit 3 is 100Hz, which meets the requirements of the terahertz pyroelectric detector. Working frequency range.

The beneficial effects of the present invention are:

1. The present invention provides a current-type terahertz pyroelectric detector readout circuit, which is suitable for reading weak current signals, and realizes the elimination of power frequency interference, filtering out unnecessary signals and Noise, amplify the signal, and control the size of the output voltage signal to match the output voltage signal with the voltage required by the back-end digital acquisition circuit.

2. In the current-voltage converter in the readout circuit provided by the present invention, a current-limiting resistor is also connected in series between the connection between the feedback circuit and the output end of the terahertz pyroelectric detector and the inverting input end of the operational amplifier, which can effectively Prevent the damage to the operational amplifier caused by instantaneous high-voltage discharge caused by static electricity or plugging and unplugging the power supply.

3. The 50Hz notch circuit in the readout circuit provided by the present invention can effectively eliminate power frequency signal interference, and at the same time, the positive and negative power supplies of the 50Hz notch circuit are connected with large capacitors to filter out power supply pulsation interference. The F42N50 module used in the 50Hz notch circuit has higher precision, stability and lower noise.

4. In the feedback circuit of the first-order low-pass filter amplifying circuit in the readout circuit provided by the present invention, the feedback resistor is formed by series connection of a fixed resistor and a sliding rheostat, and the magnification can be adjusted by adjusting the sliding rheostat.

5. In the potential raising module in the readout circuit provided by the present invention, a sliding rheostat and a fixed resistor are used in series in the voltage dividing circuit connected to the positive phase terminal of the operational amplifier, and the lifting multiple of the voltage can be adjusted by adjusting the sliding rheostat to output A voltage signal that matches the voltage required by the back-end digital acquisition circuit.

6. In the current-voltage converter in the readout circuit provided by the present invention, the operational amplifier is an AD8627 operational amplifier, which has an extremely low bias current, the maximum being only 1pA, and is suitable for terahertz pyroelectric detectors Collection and output of weak current.

7. The current-voltage converter in the readout circuit provided by the present invention can realize the amplification factor of 109V/A.

Description of drawings

Fig. 1 is a block diagram of the circuit structure of the readout circuit of the current mode terahertz pyroelectric detector provided by the present invention.

Fig. 2 is a circuit diagram of the current-voltage converter in the readout circuit of the current-mode terahertz pyroelectric detector provided by the present invention.

Fig. 3 is a circuit diagram of the 50Hz trap circuit in the readout circuit of the current-mode terahertz pyroelectric detector provided by the present invention.

Fig. 4 is a circuit diagram of the first-order low-pass filter amplifier circuit in the readout circuit of the current-mode terahertz pyroelectric detector provided by the present invention.

Fig. 5 is a circuit diagram of the potential raising module in the readout circuit of the current-mode terahertz pyroelectric detector provided by the present invention.

In the figure: R1-R8, R10, R11, R13: resistors, R9, R12: sliding rheostats, C2-C5: capacitors, U1-U3: operational amplifiers

Detailed ways

The present invention will be further introduced below in conjunction with the accompanying drawings and embodiments.

A current-mode terahertz pyroelectric detector readout circuit, as shown in Figure 1, includes a current-voltage converter, a 50Hz trap circuit, a first-order low-pass filter amplifier circuit, and a potential raising module. Among them, the signal output by the terahertz pyroelectric detector is input into the current-voltage converter, which is used to convert the current signal into a voltage signal; the signal output by the current-voltage converter is input into the 50Hz trap circuit, which is used to eliminate power frequency interference; 50Hz The signal output by the notch circuit is input into the first-order low-pass filter amplifier circuit for further signal amplification; the signal output by the first-order low-pass filter amplifier circuit is then input into the potential raising module, which is used to raise the voltage so that the voltage signal output by the circuit is consistent with the back-end The digital acquisition circuit needs to match the voltage.

The circuit diagram of the current-to-voltage converter is shown in Figure 2. Among them, the current-voltage converter uses the AD8627 operational amplifier as the core, the signal output terminal of the terahertz pyroelectric detector is connected to the inverting input terminal of the AD8627 operational amplifier, and the ground terminal of the detector is connected to the non-inverting input terminal of the AD8627 operational amplifier. The feedback resistor R1 is 1GΩ, so that the amplification factor of 109V/A can be obtained, the feedback capacitor C2 is 10pF, and the inverting input terminal of AD8627 is connected in series with a 10kΩ resistor R2.

The circuit diagram of the 50Hz notch circuit is shown in Figure 3. The 50Hz notch circuit is based on the F42N50 module. The positive and negative power supplies of the F42N50 module are connected in parallel with 2.2μF capacitors (C3 and C4) to filter out the power supply ripple and make the notch module work more stably; the input terminal is connected with a 180kΩ resistor R3; a 1kΩ resistor R4 is connected between the RQ terminal and the ground; a 180kΩ resistor R5 is connected between the RG terminal and the output terminal to stabilize the output.

The circuit diagram of the first-order low-pass filter amplifier circuit is shown in Figure 4. The first-order low-pass filter amplifier circuit is based on the LM324 ordinary operational amplifier. Its feedback capacitor C5 is 18nF. The feedback resistor is composed of a 100KΩ fixed resistor R7 and a sliding rheostat R9 with a resistance value of 2MΩ. The resistance of the positive input terminal of the operational amplifier is R8 is 10kΩ, the magnification of the circuit is adjustable from 10 to 200 times, and the inverting terminal resistance R6 is 10kΩ.

The circuit diagram of the potential raising module is shown in Figure 5. The potential raising module first cooperates with a 100kΩ fixed resistor R11 and a 100kΩ sliding rheostat R12 to raise the potential to 1/2Vcc~Vcc, and the divided potential is input to the positive phase terminal of the LM324 operational amplifier, and the feedback resistor R13 and The resistors R10 at the inverting terminal are all 10kΩ, so that the signal and the boosted level form a double summation circuit, which can minimize the interference of power supply noise on the final output signal without reducing the signal amplitude.

Claims (6)

1. a current mode Terahertz pyroelectric detector sensing circuit, comprise current-voltage converter (1), 50Hz trap circuit (2), single order low-pass filtering amplifying circuit (3) and current potential lifting module (4), the signal of Terahertz pyroelectric detector output is inputted described current-voltage converter (1), for current signal is converted to voltage signal, the signal of described current-voltage converter output is inputted described 50Hz trap circuit (2), being used for eliminating power frequency disturbs, the signal of described 50Hz trap circuit output is inputted described single order low-pass filtering amplifying circuit (3), for further amplifying signal, the signal of described single order low-pass filtering amplifying circuit output is inputted described current potential lifting module (4) again, for lifting voltage, described current-voltage converter (1) comprises Terahertz pyroelectric detector signal output part, operational amplifier and feedback circuit, Terahertz pyroelectric detector signal output part is connected with the inverting input of operational amplifier, the ground end of Terahertz pyroelectric detector is connected with operational amplifier normal phase input end, feedback circuit is connected between the inverting input of operational amplifier and the output terminal of operational amplifier, and feedback circuit is by feedback resistance and feedback capacity parallel connection.

2. current mode Terahertz pyroelectric detector sensing circuit according to claim 1, it is characterized in that, in described current-voltage converter (1), between the junction of feedback circuit and Terahertz pyroelectric detector output terminal and the inverting input of operational amplifier, be in series with current-limiting resistance.

3. current mode Terahertz pyroelectric detector sensing circuit according to claim 1, is characterized in that, the feedback resistance in described single order low-pass filtering amplifying circuit (3) is in series by fixed resistance and slide rheostat.

4. current mode Terahertz pyroelectric detector sensing circuit according to claim 1, is characterized in that, in described current potential lifting module (4), adopts slide rheostat and fixed resistance series connection with operational amplifier normal phase input end in the bleeder circuit being connected.

5. current mode Terahertz pyroelectric detector sensing circuit according to claim 1, is characterized in that, the operational amplifier in described current-voltage converter (1) is AD8627 operational amplifier.

6. current mode Terahertz pyroelectric detector sensing circuit according to claim 1, is characterized in that, described 50Hz trap circuit (2) is taking F42N50 module as core.