System and method for a dual bandwidth capacitor multiplying filter

The present invention is related to a filter circuit that allows preamplifiers, such as those used in hard disk drives, to quickly recover from transients such transients caused by power switching, write to read switching, and thermal asperity. According to an embodiment of the present invention, under normal conditions, such as signals at 100 KHz to 10 MHz, signals at medium frequencies, such as signals at 100 KHz to 10 MHz, pass through a low pass filtering circuit. When a transient signal is received, then a change in voltage for Vout of the low pass filtering circuit increases by more than 100*Vout. For example, during transient conditions, the low pass filter circuit may also pass signals ranging from 10 MHz to 100 MHz. Accordingly, under transient conditions, the low pass pole moves approximately 100 times or more. A feedback loop subtracts the resulting low pass signals from the original signal, acting as a high pass filter. The overall circuit recovers quickly from the transient by adjusting for the tail end of the transient. Transient conditions may include a signal that is low frequency or higher amplitude or both. As the transient condition disappears, then the filter circuit resumes normal operation.