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# Differential Symmetry Restore without Frequency Change

IP.com Disclosure Number: IPCOM000103809D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 62K

IBM

## Related People

Mikos, JF: AUTHOR

## Abstract

A method for restoring symmetry to a differential signal without changing the frequency of the signal is disclosed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 60% of the total text.

Differential Symmetry Restore without Frequency Change

A method for restoring symmetry to a differential signal
without changing the frequency of the signal is disclosed.

The basic idea is shown in Fig. 1.  An asymmetric differential
signal is the given input (PIN-NIN), while a symmetric differential
signal is the desired output (POUT-NOUT).  The idea is to create a
differential sawtooth shaped signal (C0-C1) whose peak amplitude is
symmetric about the differential switching point (i.e., the positive
peak differential voltage equals the negative peak differential
voltage).  When this sawtooth waveform is fed into a differential
gain stage, a symmetric output signal will result (POUT-NOUT).

The sawtooth signal may be obtained by differentially charging
a timing capacitor.  Note that the charging current must be different
for the up and down cycles of the input, because the signal must
swing the same voltage amount in different amounts of time.  To
accomplish this, the peak value of the sawtooth waveform will be
detected, and the charging current adjusted separately for the up and
down time until the voltage peaks are equal.

The block diagram is shown in Fig. 2.  The differential input
signal is fed to PIN,NIN where it is used to create the sawtooth
signal.  The differential timing capacitor is charged by currents
which are different for the two sides of the circuit.  These currents
are determined by the peak detectors and an...