Threshold Follower Circuit
Original Publication Date: 1985-Jun-01
Included in the Prior Art Database: 2005-Feb-18
A threshold follower circuit is a solution to undesired pulse-width modulation due to amplitude variation in a fiber-optic link. As a result, the crossover point of the incoming signal in relation to the threshold remains the same so that the resulting output pulse maintains a constant duration. With no signal at EI 11, the circuit parameters are chosen such that, in the quiescent state, the current through diode 12 (I1 + I2) is equal to the emitter current I3 of transistor 16, as shown in Fig. 1. This causes the DC voltage drop from base to the emitter of transistor 16 to equal the voltage drop from the anode to cathode of diode 12. The actual voltage at the cathode of diode 12 is higher than the voltage at the emitter of transistor 16 by an amount equal to the voltage drop across resistor 17.