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The group delay and phase delay properties of a linear time-invariant (LTI) system are functions of frequency, giving the time from when a frequency component of a time varying physical quantity—for example a voltage signal—appears at the LTI system input, to the time when a copy of that same frequency component—perhaps of a different physical phenomenon—appears at the LTI system output.
An ideal delay line characteristic has constant attenuation and linear phase variation, with frequency, i.e. it can be expressed by =where τ is the required delay.. As shown in lattice networks, the series arms of the lattice, za, are given by
A phase equalizer is a circuit which is cascaded with a network in order to make the overall phase response more linear (or to make the group delay more constant). The combined circuit will transmit waveforms with improved fidelity, compared to the performance of the initial network alone. Phase equalization is often necessary because many ...
Gain and group delay of the third-order Butterworth filter with = The group delay is defined as the negative derivative of the phase shift with respect to angular frequency and is a measure of the distortion in the signal introduced by phase differences for different frequencies. The gain and the delay for this filter are plotted in the graph ...
Group delay can be different at different frequencies (as by band-limited passive loudspeakers or microphones), or it can be (roughly) constant for certain circuits, e.g., delay lines, and you cannot observe time-smearing of frequencies within the limited frequency band where group delay is constant (i.e., phase response is linear).
Compared to finite-order approximations of the Gaussian filter, the Bessel filter has a slightly better shaping factor (i.e., how well a particular filter approximates the ideal lowpass response), flatter phase delay, and flatter group delay than a Gaussian filter of the same order, although the Gaussian has lower time delay and zero overshoot. [8]
The transfer function of a two-port electronic circuit, such as an amplifier, might be a two-dimensional graph of the scalar voltage at the output as a function of the scalar voltage applied to the input; the transfer function of an electromechanical actuator might be the mechanical displacement of the movable arm as a function of electric ...
The bridged T topology is used for delay equalisation, particularly the differential delay between two landlines being used for stereophonic sound broadcasts. This application requires that the filter has a linear phase response with frequency (i.e., constant group delay) over a wide bandwidth and is the reason for choosing this topology.