Wave Shaping

RC Differentiator

The circuit is a variable RC differentiator with emitter followers to isolate both the input and output of the circuit. The input emitter follower is composed of Q₁, R₁, and emitter resistor R₂. The signal is applied through the current limiting resistor R₁ to the base of Q₁. The differentiator circuit is composed of C₁, R₃, and variable resistor R₄. By varying the arm of R₄, the amount of resistance can be increased or decreased, thus changing the time constant of the circuit. Since C₁ is relatively small and the sum of R₃ and R₄ is small, the circuit will have a short time constant which will prevent the passage of low frequency signals.

R₅ couples the signal to the base of the output emitter follower while R₆ provides a negative bias to maintain Q₂ in the linear portion of its operation. The emitter of Q₂ is connected through the variable resistor R₇ and the resistor R₈ to the positive supply. R₇ provides a method of adjusting the output DC level with a minimum effect on the AC signal.

R₉, C₂, and R₁₀, C₃ form filtering networks.