NEW Phase locked amplifier AD630 module minimum system phase sensitive detection weak signal conditioning
I. Overview
The AD630 is a balanced modem with high dynamic range. When configured as a lock-in amplifier, it can recover small signals from l00dB of interference noise. The internal phase sensitive detector is based on the switch multiplication structure to ensure its operation. Accuracy and stability, the internal resistance is the use of high-precision SiCr thin film resistors, internal compensation capacitors, only need to connect the chip pins to work stably in the closed-loop gain. The integrated resistor network inside the chip can be configured with a precision closed-loop gain of ±1 and ±2. It is also possible to use an external feedback resistor to achieve the special required function.
Second, the characteristics
1. Can recover signal from 100 dB noise
2. Bandwidth: 2 MHz channel bandwidth
3. Slew rate: 45 V/us
4. Low crosstalk: -120 dB at 1 kHz and -100 dB at 10 kHz
5. Gain: Pin programmable, closed loop gain of ±1 and ±2
6. Bandwidth: 350 kHz full power bandwidth
7. Gain accuracy: 0.05% closed loop gain accuracy
8. Offset voltage: 100μV channel offset voltage
Third, the application
Balanced modulation, demodulation
2. Synchronous detection
3. Phase detection
4. Orthogonal detection
5. Phase sensitive detection
6. Lock-in amplification
7. Square wave multiplication
Five, circuit description
Lock-in amplifier mode
Connection: M1-B3, M1-B4, M1-B6 (amplified by the same direction amplifier, gain = 1+R2/R1)
Disconnected: other
Input: signal to be tested -> VIN, reference signal (usually square wave) -> REFIN
Output: VOUT -> RMS of the useful frequency signal in the signal to be tested
Remarks:
1) The lock-in amplifier output passes through a fourth-order low-pass filter (cutoff frequency is 0.1Hz), indicating the effective value of the useful frequency signal.
2) To test the signal before passing through the low-pass filter, test TP1.
2. Balanced modulator mode
Connection: M2-B1, M2-B2, M2-B5 (not directly input through the amplifier)
Disconnected: other
Input: baseband signal -> VIN, reference signal (typically square wave) -> REFIN
Output: VOUT -> modulated signal
Remarks:
1) This mode can also be used as a precision rectifier. Input the same signal to both inputs.
2) This mode can also be used as a balanced demodulator, VIN input modulation signal, REFIN input carrier signal, VOUT output unfiltered baseband signal, so an appropriate low-pass filter is needed to filter out the low-frequency baseband signal.
3. Other instructions
1) The supply voltage is plus or minus 5V to plus or minus 18V
2) The output of the low-pass filter is a DC signal whose magnitude is proportional to the effective value of the signal component of the input signal that is the same as the frequency of the reference signal, ie ****
3) The higher the cut-off frequency of the low-pass filter, the faster the lock-in amplifier locks, but the greater the error of the output DC signal.
Second, test the picture
Verification of the relationship between the phase difference of the input signal of the AD630 and the output waveform:
When the phase difference between the input signal and the reference signal is 0, the TP1 output is as shown below:
When the phase difference between the input signal and the reference signal is 90°, the TP1 output is as shown below.
When the phase difference between the input signal and the reference signal is 180°, the TP1 output is as shown below:
When the phase difference between the input signal and the reference signal is 270°, the TP1 output is as shown below:
For waveform analysis, when the phase difference is 0, the output waveform is all higher than 0, that is, the output voltage reaches a positive maximum value. When the phase difference is 90, the output waveform has a DC component of 0, that is, the output voltage is 0. When the phase difference is 180, the output voltage reaches a negative minimum value, and when the phase difference is 270, the output voltage is 0.