Posted on Oct 6, 2012

Many applications require control signals that have phase shifts with reference to an input signal. Circuit accepts a sine, square, or triangular wave as an input reference signal and produces square-wave outputs with 0`, 90`, 180`, and 270` phase shifts with respect to the input. Figure 38-3B shows the input and output waveforms. The circuit contains two !Cs: an LM565 phase-locked loop and a 7474 dual-D positive edge-triggered flip-flop. R1 and C1 set the free-running frequency of the LM565`s VCO. You should adjust R1 so that the frequency is approximately four times that of the input reference signal.

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The LM565 responds to input signals greater than 10 mV pk-pk; 3 V pk-pk is the chip"s maximum allowable input level. Q1 matches the LM565"s output to the flip-flops" inputs. The flip-flops" outputs provide the TTL-compatible square-wave signals with 0", 90", 180", and 270" phase shift with reference to the input signal.

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