Low-voltage current-mode CMOS IC continuous-time filters with orthogonal ω0-Q tuning

The design of fully differential high-frequency continuous-time current-mode filters in digital CMOS technology is presented. A universal biquad is constructed from two basic building blocks, lossless and lossy differential current-mode integrators. The circuits are very simple, can readily be integrated, are suitable for high-frequency applications, and can operate with a power supply as low as 3 V. Pole frequency ω₀ and quality factor Q are tuned orthogonally by means of a translinear circuit. The orthogonal ω ₀-Q tuning method permits the design of digitally programmable analog filters where all programming activities take place in the DC bias circuitry, with no switches and their unavoidable parasitics in the signal path. The design is illustrated on a 100 MHz fifth-order cascade lowpass filter, simulated for a standard 0.6 μ digital CMOS process. With 3 V supply voltage and 100 μA bias current, power dissipation equals 4.2 mW per biquad. Total harmonic distortion (THD) was simulated to be -84 dB. Implementations in bipolar, CMOS, or biCMOS are possible; no special technology is required