  In this paper a CMOS operational amplifier is presented which operates at 2V
power supply and 1microA input bias current at 0.8 micron technology using non
conventional mode of operation of MOS transistors and whose input is depended
on bias current. The unique behaviour of the MOS transistors in subthreshold
region not only allows a designer to work at low input bias current but also at
low voltage. While operating the device at weak inversion results low power
dissipation but dynamic range is degraded. Optimum balance between power
dissipation and dynamic range results when the MOS transistors are operated at
moderate inversion. Power is again minimised by the application of input
dependant bias current using feedback loops in the input transistors of the
differential pair with two current substractors. In comparison with the
reported low power low voltage opamps at 0.8 micron technology, this opamp has
very low standby power consumption with a high driving capability and operates
at low voltage. The opamp is fairly small (0.0084 mm 2) and slew rate is more
than other low power low voltage opamps reported at 0.8 um technology [1,2].
Vittoz at al [3] reported that slew rate can be improved by adaptive biasing
technique and power dissipation can be reduced by operating the device in weak
inversion. Though lower power dissipation is achieved the area required by the
circuit is very large and speed is too small. So, operating the device in
moderate inversion is a good solution. Also operating the device in
subthreshold region not only allows lower power dissipation but also a lower
voltage operation is achieved.
