The variable gain bootstrap active load: a new approach to amplifier voltage gain enhancement and control

This work describes a novel technique for obtaining controllable, high-voltage gain in amplifier circuits where current mirrors and cascading techniques cannot be used. An example of this is in high-frequency design where suitable complementary devices are generally not available. Although the method was originally intended for use in the design of operational transconductance amplifiers (OTAs) implemented in GaAs MESFET technology for use in high-precision filtering applications, it can be applied to other types of gain stage and implemented in other technologies. For example, using the new technique, controllable gains in excess of 40 dB can be obtained using standard GaAs MESFET technology without reliance on device width ratioing or on early saturation. The application of the OTA design in an integrated continuous-time bandpass filter chip is presented with encouraging preliminary results