A 10.7-MHz fully balanced, high-Q, 87-dB-dynamic-range current-tunable Gm-C bandpass filter

A 10.7-MHz fully balanced, high-Q, wide-dynamic-range current-tunable Gm-C bandpass filter is presented. The technique is relatively simple based on two fully balanced components, i.e. an adder and a low-Q-based bandpass filter. The Q factor is approximately equal to a typically high and constant value of a common-emitter current gain (beta) and is, for the first time, independent of variables such as a center frequency. Possible solutions for good stability of the Q factor with temperature are suggested. Not only can the need for additional Q-tunable circuits be greatly reduced, the sensitivity of the Q factor can be greatly improved. Sensitivities of either the Q factor or the center frequency are constant between 1 and -1 and are no longer strongly affected by the Q factor or variables. As a simple example at 10.7 MHz, the paper demonstrates the high-Q factor of 121, the low total output noise of 5.303 mu V-rms, the 3rd-order intermodulation-free dynamic range (IMFDR3) of 74.45 dB and the wide dynamic range of 87.45 dB at 1% IM3. The center frequency is current tunable over three orders of magnitude. Comparisons to other 10.7-MHz Gm-C approaches are also included.