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What problem arise in comparator circuit when noisy sinusoidal waveform is applied?
A problem arises with the comparator when the input signal is noisy. If the comparator is fast enough, the output can jitter back and forth between the HIGH and LOW states. This can be unacceptable if the output is to be connected to a high-speed digital circuit.
What is the effect of noise in comparator circuit?
A comparator normally changes its output state when the voltage between its inputs crosses through approximately zero volts. Small voltage fluctuations due to noise, always present on the inputs, can cause undesirable rapid changes between the two output states when the input voltage difference is near zero volts.
Why is the output of a comparator buffered?
This reference voltage has relatively high output impedance, since it is designed to be input to a comparator; therefore, this output should be buffered in most cases. Without a buffer circuit, you can still look at the output voltage using a high-impedance input like a voltmeter or an oscilloscope.
How does the state of a comparator change?
The shift of the state of its output depends on the direction of passage through zero of voltage v B applied at the input of this comparator. Voltage v B evolves in time according to a negative slope, starting from value (V CC /2). At t = τ = R 1 .C 1, voltage v B reaches and drops below zero (v B becomes slightly < 0).
When does the voltage of a comparator go to zero?
At t = τ = R 1 .C 1, voltage v B reaches and drops below zero (v B becomes slightly < 0). The output state of the comparator shifts from the high state to the low state. Moreover, at this precise instant, the value of voltage v B goes to − V CC due to the abrupt passage of v A from + V CC to − V CC.
How is the phase comparator output signal formed?
The phase comparator output signal is formed by a signal rich in harmonics. This signal is the result of the comparison of the reference signal ve and signal v S provided by the output of the VCO. The signal at the phase comparator output also contains a slowly varying component that is retrieved at the output of the low-pass filter.