Detection and correction of asymmetric transient signals

An apparatus for detecting asymmetry in transient signals of an input signal, the apparatus comprising:

• a pre-shoot filter (1) for receiving an input signal and asymmetrically filtering it utilizing a first set of filter coefficients to provide a first output in which substantially only pre-shoots of input transient signals are present;
• an after-shoot filter (2) for receiving the input signal and asymmetrically filtering it utilizing a second set of filter coefficients to provide a second output in which substantially only after-shoots of input transient signals are present;
• and
• summing and comparison means (3 to 11) for summing the first outputs over a predetermined time interval, summing the second outputs over the predetermined time interval and comparing first and second summed outputs to give an output signal indicating whether pre-shoots or after-shoots predominate over the predetermined time interval.

A peaking filter (14-19;

• 23-26), comprising:
• means for receiving a detection signal indicating whether pre-shoots or after-shoots are found to systematically predominate in transients of an input signal;
• and
• means for varying filter coefficients of the peaking filter in accordance with the detection signal to provide a corrected output in which transients are substantially symmetrical.

A peaking circuit according to claim 11, wherein said peaking filter (14, 15, 17) for performing peaking correction on the input signal comprises an FIR filter comprising:

• a delay line (14) for receiving the input signal and having a plurality of outputs (140 . . . 144);
• a plurality of multipliers (150 . . . 154) each having a first input terminal connected to a respective individual output (140 . . . 144) of the delay line (14) representing a multiplicand and each having a second input terminal for receiving a respective filter coefficient representing a multiplier and each having an output terminal for outputting a respective product;
• and
• a summing circuit (17) for receiving the respective products from the multipliers (150 . . . 154), summing them and providing a summed output, wherein said filter coefficients are variable such that if neither pre-shoots nor after-shoots are found to predominate in transients of the input signal then said coefficients are determined purely based upon a desired amount of peaking required and an impulse response of the filter will be symmetrical, whereas if pre-shoots are found to predominate then said coefficients are varied so as to provide an asymmetrical impulse response in which additional after-shoots are produced, and if after-shoots are found to predominate then said coefficients are varied so as to provide an asymmetrical impulse response in which additional pre-shoots are produced.