Lattice phase equaliser

A lattice phase equaliser or lattice filter is an example of an all-pass filter. That is, the attenuation of the filter is constant at all frequencies but the relative phase between input and output varies with frequency. The lattice filter topology has the particular property of being a constant-resistance network and for this reason is often used in combination with other constant-resistance filters such as bridge-T equalisers. The topology of a lattice filter, also called an X-section, is identical to bridge topology. The lattice phase equaliser was invented by Otto Zobel^[1]^[2] using a filter topology proposed by George Campbell.^[3]

^ Zobel, O J, Phase-shifting network, US patent 1 792 523, filed 12 March 1927, issued 17 Feb 1931.
^ Zobel, O J, Distortion Compensator, US patent 1 701 552, filed 26 June 1924, issued 12 Feb 1929.
^ Darlington, S, "A history of network synthesis and filter theory for circuits composed of resistors, inductors, and capacitors", IEEE Trans. Circuits and Systems, vol 31, pp. 3–13, 1984.

[1] Zobel, O J, Phase-shifting network, US patent 1 792 523, filed 12 March 1927, issued 17 Feb 1931.

[2] Zobel, O J, Distortion Compensator, US patent 1 701 552, filed 26 June 1924, issued 12 Feb 1929.

[Darlington-3] Darlington, S, "A history of network synthesis and filter theory for circuits composed of resistors, inductors, and capacitors", IEEE Trans. Circuits and Systems, vol 31, pp. 3–13, 1984.

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