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Browse Prior Art Database

Differential Loss of Signal Detector

IP.com Disclosure Number: IPCOM000110453D
Original Publication Date: 1992-Nov-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 1 page(s) / 59K

Publishing Venue

IBM

Related People

Holstein, WH: AUTHOR [+4]

Abstract

A low-power differential loss of signal detector is disclosed. This circuit will flag the loss of signal condition in a differential amplifier while consuming only 4 milliwatts. The differential nature of this circuit allows for both true and complemented outputs, LOS and NLOS, respectively.

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This is the abbreviated version, containing approximately 76% of the total text.

Differential Loss of Signal Detector

      A low-power differential loss of signal detector is disclosed.
This circuit will flag the loss of signal condition in a differential
amplifier while consuming only 4 milliwatts.  The differential nature
of this circuit allows for both true and complemented outputs, LOS
and NLOS, respectively.

      Figure 1 illustrates how this circuit would be used.  The
circuit functions as follows.  Transistors Q1 and Q2 are wire Ored
together to function as a single input.  The combination of Q3, Q4,
and RC1 form a high gain inverting amplifier.  Transistors Q5 and Q6,
along with connected resistors, form an emitter- coupled differential
pair.  Transistors Q7 and Q8 establish a reference voltage for one
side of this pair.  The inverting amplifier acts as the second input
to the differential pair.  When the base of Q5 rises above the
reference on the base of Q6, the LOS signal will go high.  NLOS will
simultaneously go low.  This will occur only when both IN1 and IN2
fall below 2.1 volts.

      By design, depending on the state of the input, the circuit
will drive either transistor Q3 or Q5 hard into saturation to take
advantage of their base-to-collector capacitance as storage elements.
During normal operation when IN1 and IN2 cycle above the 2.1 volt
threshold, Q3 is driven into saturation.  When both inputs fall
simultaneously, this capacitance must discharge through a 18K ohm
path before LOS switches high.  This dis...