Deadband circuits find applications in servo-control systems. A precisio current source and a half-wave inverting rectifier form a positive dead band circuit (Figure 1). The REF01, IC1, is a precision 10V voltage reference. It forms a precision current source with the addition of a unity-gain buffer (IC2A) and resistor R1. IC2A forces the ground pin (Pin 4) of IC1 to assume the potential at IC2A’s non inverting input. IC1 forces its highly accurate reference voltage (10V) across R1, so the current I1 through R1 is 10V/R1. Because the inverting input of IC2B connects to the output of the current source, the feedback diode, D1, becomes forward-biased with current I1. The forward-biased diode keeps the output of IC2B at approximately –0.6V. Because the cathode end of D2 stays at virtual ground through R3, D2 remains reverse-biased. Hence, VOUT remains at virtual ground ( 0 V). Any positive voltage applied to VIN further forward- and reverse - biases D1 and D2, respectively, and the output remains at 0V (deadband zone) for VI N> 0 V. Negative inputs tend to forward-bias D2 and reverse- bias D1. This bias situation occurs only when the current through R2 (because of the negative VI N) equals or exceeds 10V/R1. So, the output is 0V (de adband) until VIN reaches a value equal to –10R2/ R1. If you choose R1=20 kV, VO U T remains at 0V for VIN> ( – 5 V); for VI Nm ( – 5 V) , VOUT= ( – VIN– 5 V). Figure 2 shows the transfer function for this scenario. C1, C2, and C3 a re decoupling capacitors for IC1 and IC2. R4 reduces the offset voltage of IC2B in the non deadband region . You could realize an alternative straight-forward circuit by prebiasing the inverting half-wave rectifier through a precision resistor connected to a voltage reference without using the unity-gain buffer, IC2A. However, this alternative would increase the noise gain, thereby increasing the offset and noise at the output.
