Resistive broadbanding

Resistive broadbanding is a technique that can be applied to increase the frequency of a pole associated with an independent capacitor voltage or an independent inductor current, while maintaining the contribution of this sub-network to the gain-pole product.

Insertion of resistors into the signal path

Fig. 424 Resistive broadbanding A. Circuit with single-pole voltage transfer: \(H(j\omega)=\frac{V_o}{V_i}\) B. \(R_b\) in parallel with \(C\) implements resistive broadbanding C. Magnitude characteristics of the voltage transfers from circuits A and B.

Resistive broadbanding can be done by inserting a resistor in parallel with a capacitor or in series with an inductor. Fig. 424 illustrates the first method. We have already illustrated the method for compensation of the transimpedance amplifier in example example-transimpedancePZcancel. There, resistive broadbanding was implemented by placing a resistor in parallel with the input of the operational amplifier.

Interaction with other performance aspects

Resistive broadbanding can be regarded as a brute force method for exchanging controller gain with controller bandwidth. If it is done at the input of the controller, the noise penalty, as well as the penalty on the DC error and the temperature drift thereof, can be large. If it is done at stages that carry a large signal level, e.g., at the output of the controller, the penalty on the power efficiency may be large. In general, reduction of the midband loop gain by means of resistive broadbanding will result in a degraded performance of the feedback amplifier.