Current-mode amplifiers

Traditional voltage-feedback amplifier configurations, both discrete and integrated, have always suffered from the severe disadvantage of drastically restricted bandwidth at high gains due to the problem of constant gain-bandwidth product. The author shows how adopting a current-mode approach to a range of amplifier designs based on current conveyors enables high grain and wide bandwidth to be achieved simultaneously with the added bonus of increased slew rates. Applying current feedback around a conveyor amplifier is shown to improve performance even further, achieving a 40-dB voltage gain at a bandwidth of 3.3 MHz. A new conveyor instrumentation amplifier format is presented that enables an intrinsically high current-mode rejection ratio to be obtained without the need for any resistor matching