Class Discussion: Clock Timing

A clock signal must be implemented on board to drive the LED driver circuit. By repeatedly flashing LED's on an off modulation is achieved. The photons from LED's after passing through fingertip are received on a photo diode. This signal then must be demodulated back to baseband.

The question is: If the clock for S/H demodulator is out of phase or delayed from clock driving LED's then will error occur and how can it be fixed. The problem could arise from delays in the circuit. The oscillator is designed as a simple charging RC circuit with dual inverters. There exists a delay in switching of inverters.

To match clocks a phase delay of some sort must be introduced in the circuit. A simple RC delay can be introduced providing a phase of 45 degrees and can be cascaded to the desired result. This result assumes the delay is constant and a multiple of 45 degrees. A more complex delay network could be developed to provide variable tuning delay with a potentiometer or variable capacitor. If inductors are allowed in the design, then a maximum phase of 90 degrees could be achieved.