A 15 MHz 20 mW BiCMOS switched-capacitor biquad operating with 150 Ms/s sampling frequency

In order to increase the sampling frequency of SC filters the Precise Opamp Gain (POG) design approach is presented. It is based on the use of large bandwidth opamps with low but precise dc-gain. The finite gain value is taken into account in the design phase. This produces capacitor values slightly different from those obtained with the standard design. A BiCMOS opamp with a nominal gain of 96 and unity-gain frequency of 650 MHz is used in a biquadratic lowpass filter with Q = 2.8 designed with the POG approach. In a 1.2 µm BiCMOS technology, the prototype lowpass biquad operates with sampling frequency up to 150 Ms/s with 0.2 dB accuracy in the transfer function. For a sampling frequency of 150 Ms/s, the cutoff frequency is 15 MHz. The dynamic range (for 1% THD) is 67 dB, and THD is less than –60 dB for a 1.5 Vpp 5 MHz input signal. The chip area is 1 mm2, and the power consumption is 20 mW. © 1995 IEEE