A Continuously Adjustable Video-Frequency Current Amplifier for Filter Applications

The adjustable balanced-signal current amplifier presented in this paper amplifies a current by first transforming it into a voltage signal using two poly-silicon resistors and then back into a current signal using a single MOSFET resistor operating in the linear region. We implemented the amplifier in the double-poly 0.6 μm CMOS process by Austria Mikro Systeme International. It consumes 12.4 mW from a 3.3 V supply and covers an area of 0.07 mm2. Measurements show that it is suitable for building biquadratic filters with a spurious-free dynamic range of more than 45 dB, a pole Q of 3 and a pole frequency of up to 900 kHz. We also show that a modification of the circuit allows building filters with pole frequencies up to 6 MHz.