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Absolute Value Envelope Detector Scheme using Three-Input Comparators

IP.com Disclosure Number: IPCOM000116756D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 82K

Publishing Venue

IBM

Related People

Greene, RA: AUTHOR [+2]

Abstract

An envelope detector using a three-input comparator reduces power and area by reducing the number of comparators required to generate the envelope. The result is an absolute value envelope detector with high performance while consuming less power and chip area than conventional envelope detectors.

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Absolute Value Envelope Detector Scheme using Three-Input Comparators

      An envelope detector using a three-input comparator reduces
power and area by reducing the number of comparators required to
generate the envelope.  The result is an absolute value envelope
detector with high performance while consuming less power and chip
area than conventional envelope detectors.

      By using an absolute value scheme, we can compare the
differential signal amplitude to given reference thresholds with only
one comparator per threshold instead of two comparators per
threshold.  The comparison is done by a three-input-to-two-output
bipolar differential pair which is eventually converted to a
single-ended signal.

      The signal comes as inputs to two emitter followers in the
threshold circuit (Fig. 1); the signals are then down-shifted by an
amount determined by the voltage drop across resistors R7, R13, R4,
R5, R8, R2, R10, and R9.  The voltage drop over R29 is used to make
the voltage across the current source in the reference
emitter-follower match that of the signal emitter-followers (Q0 and
Q1).  The OUTR0 pin is the reference voltage against which the
signals at OUTP3, OUTN3, OUTP4, OUTN4, OUTP5, and OUTN5 are compared;
the OUTR5 pin can be used to simulate a two-input comparator (if
desired for some timing issue) that still matches a three-input
comparator by tying the pin to one of the signal inputs of the
comparator.

      The comparator (Fig. 2) receives the signals from the threshold
circuit as inputs to three emitter-followers.  The plus and minus
outputs at the emitters of Q10 and Q11 are input to Q2 and Q6 whose
collectors are tied together, and the reference output at the emitter
of Q4 is input to Q9--the other side of the differential pair.  Th...