Dynamically biased 1 MHz low-pass filter with 61 dB peak SNR and 112 dB input range

Dynamically varying the bias currents in a filter normally causes unacceptable disturbances at its output. This filter has bias currents that can be varied over several orders of magnitude for optimum power consumption and noise at each total input signal level-without disturbing the output. Although the filter is internally nonlinear and time-varying, it is externally linear and time-invariant. The chip uses the first-order log-domain filter.