A capacitor is charged and discharged through switch selectable resistors from regulated DC voltage supplies and clamping diodes to provide the bias signal to control the rise and fall times of the RF output pulse of a PIN diode attenuator. An isolation buffer isolates charging and discharging transients from the bias signal. An adjustable AC gain and adjustable DC offset inverting amplifier provides the isolation buffered signal to a high impedance, very low output AC impedance source for driving the bias input of the PIN diode attenuator. The DC offset is provided by an adjustable regulated voltage source coupled to the inverting amplifier.