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Emitter Detect Circuit With Gain Compensation and Hysteresis

IP.com Disclosure Number: IPCOM000051796D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 83K

Publishing Venue

IBM

Related People

Craig, TP: AUTHOR [+3]

Abstract

Circuitry for use with an optical coupler in an emitter motion detector of the kind used in typewriters compensates for response variations among individual optical couplers and also provides a hysteresis effect so that slight reverse motion of the emitter wheel does not trigger a false pulse.

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Emitter Detect Circuit With Gain Compensation and Hysteresis

Circuitry for use with an optical coupler in an emitter motion detector of the kind used in typewriters compensates for response variations among individual optical couplers and also provides a hysteresis effect so that slight reverse motion of the emitter wheel does not trigger a false pulse.

Referring to Fig. 1, an optical coupler 10 produces a signal S(E) indicative of emitter wheel motion which appears across load resistor R. The signal S(E) is supplied to a response (CTR) compensation circuit 12 that sends a control signal S(F) to a dependent current source 14 that supplies the drive current, the light source of optical coupler 10. In operation, the signal S(F) serves as a feedback signal for adjusting the signal S(E) to a level in accordance with a reference voltage established by a reference circuit 16.

False pulse indications are avoided by processing the signal S(E) using a hysteresis and latch circuit 18. Preferably, all of the circuits, but the optical coupler 10 and a memory capacitor 20 that cooperates with the CTR compensation circuit 12, are incorporated in a single integrated circuit module (dashed lines).

Referring to Fig. 2, a preferred circuit arrangement includes a reference circuit 16 which has diode D1 and a resistor R1 in series across the 5-volt source acting as a voltage divider to provide the reference signal S(R) to transistor T1 which is connected in a differential pair configuration with transistor T2. Transistor T2 receives the output signal S(E) of the optical coupler 10, and the transistor T3 acts as a current source of the differential pair (T1 and T2). Transistors T1, T2 and T3 cooperate with an amplifier transistor T4 to act as a comparator and produce a discharge signal S(D) across resistor R2 that assumes a state indicative of whether the signal S(E) is above or below a desired level established by the reference signal S(R). The signal S(D) is applied to a transistor T5 that controls the discharge of the memory capacitor 20 through a resistor R3.

Current for charging memory capacitor 20 is supplied through a transis...