Low Offset Voltage Comparator
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
This voltage comparator has a high AC input impedance and low offset voltage, and requires no negative supply voltage. Transistors Q5 and Q6 are current sources that are matched by conventional techniques. Q6 feeds diode configured transistor Q4, such that when Vin equals Vr, the currents as shown in the figure exist (this assumes that the VBE values of the transistors are matched as would be the case in an integrated circuit configuration). Thus, when the two signals are equals (Vin equals Vr), 2IB is available to drive transistor Q7. Since the betas of the transistors track, the emitter current of Q7 equals 2(I-IB). Resistor R3 is sized to give gain, and, therefore, transistor Q8 is saturated and Vout equals the collector-to- emitter voltage of Q8 when Q8 is saturated.