BIOLOGICAL_SIGNAL_WAVEFORM_GENERATOR

Published:2009/7/16 21:35:00 Author:Jessie | From:SeekIC

The circuit operates as follows: U1A and U1B form a triangle waveform generator, using R6 to offset the output so that it is a positive-going signal. The amplitude is set by R2 and R3, and the ramp's rate of rise is set by R1 and C1. Using the values shown, the output has an amplitude of >1 V with rise and fall times of 0.5 ms, giving a total zeta duration of 1 ms. U1C provides an inverted output of U1B. When the RESET pin on U3 is triggered, its Q1 output goes low and the short is removed across C1 by one half of the analog switch (U4). At this time, the output of U1A will be negative and the output of U1B will start to ramp up. During this time, the output of the circuit is taken from U1B via the other half of the analog switch. When the ramp reaches its positive voltage threshold, the output of U1A goes positive and U1B will start to ramp down. The output of U1A is taken via U2A and U2B (both inverting Schmitt triggers with special input circuitry that protects the input from negative voltages and allows them to level-shift) to the CLOCK input of U3. It is also taken to the analog switch, which now takes the output of the circuit from U1C (which has an output ramping up from the negative maximum to 0V). At 0 V, the output of U1A will go negative, resulting in the Q1 output of U3 going high and again shorting C1. This produces 0V output until the next trigger input resets U3 and the cycle is repeated.



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