Performance characterization of an active attenuator using two cascaded MOSFETs

The practical performance characteristics of an active voltage attenuator suitable for analog integrated circuit applications are presented. The attenuator has attractive performance characteristics including high input impedance, low power consumption, small circuit area, low noise, low THD, and precisely controllable attenuation ratio over a wide range. It can replace conventional resistor attenuators in many monolithic applications. The analysis, design, and performance of the attenuator and an amplifier employing the attenuator in the feedback loop are discussed. An attenuator which has signal to THD ratio of 61.8 dB at 100 mV input voltage, dynamic range of 75.0 dB at 1% THD, and power consumption of 106 μW for an attenuation ratio of 1:10 is readily designable with two transistors smaller than 10×10 μm ². Employing the attenuator in the feedback loop of an amplifier of gain 10, the amplifier has a signal to THD ratio of 81.5 dB at 10 mV input voltage and dynamic range of 79.3 dB at 0.168% THD