A 2.5 V active lowpass filter using all-npn gain cells with a 1 V/sub pp/ linear input range

Describes an all-npn gain cell with a highly linear V-I converter, which has a 1-V/sub pp/ linear input range and is suitable for operation at 2 V. An active LPF is used to test the transconductor. The LPF is derived from a doubly-terminated third-order Butterworth LC ladder filter prototype with 192-kHz nominal cutoff. Measured total harmonic distortion (THD) of the LPC as a function of the input voltage is shown. The maximum linear input range of 1 V/sub pp/ is achieved when the supply voltage is 2.5 V and THD is -53 dB at 10 kHz. Equi-THD curves of the LPF with the input range and the supply voltage taken as parameters are also shown.<>