• Input buffer Amplifier: Separate inputs are provided for each channel
• Gain setting amplifier: The gain of each section is controlled by a single through-hole resistor (the through hole design allows easy user modification)
• Input Bandpass filter: These sections are formed from multiple feedback filters. The centre frequency of each these filters sections have been designed for the following frequencies; (Channel 1-6.51kHz (f), Channel 2-13.02kHz (2f), Channel 3-19.53kHz (3f) and Channel 4-13.02kHz (2f)) These filter sections can be changed if an alternate fundamental modulation frequency is required
• AD630 Demodulation section; inputs to this chip are provide from the output of the bandpass filter section and the phase controller board (via the level shift circuitry). A single multiturn potentiometer provides level shifting for all the channels and is used to convert the TTL level signals from the phase controller board to zero crossing voltages on the PSD board
• Output filter: The output filters select the time constant of the control circuitry and are identical. These filters can be easily changed in order to defined the noise performance and temporal response of the measurement system

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