FEEDBACK ANALYSIS OF TRANSIMPEDANCE OPERATIONAL-AMPLIFIER CIRCUITS

The transimpedance or current feedback operational amplifier (CFB op-a mp) is reviewed and compared to a conventional voltage mode op-amp usi ng an analysis emphasizing the basic feedback characteristics of the c ircuit. With this approach the paradox of the constant bandwidth obtai ned from CFB op-amps is explained. It is demonstrated in a simple mann er that the constant gain-bandwidth product of the conventional op-amp and the constant bandwidth of the CFB op-amp are both in accordance w ith basic feedback theory and that the differences between the traditi onal op-amp and the CFB op-amp are due to different ways of controllin g the closed-loop gain. For the traditional op-amp the closed-loop gai n is altered by altering the loop gain whereas the closed-loop gain in a CFB op-amp configuration is altered by altering the input attenuati on to the feedback loop while maintaining a constant-loop gain.