CMOS low-voltage operational amplifiers with constant-gm rail-to-rail input stage

Two 3.3-V operational amplifiers with constant-g _m rail-to-rail input stage and rail-to-rail output stage are presented. The constant transconductance (g _m ) ensures a constant unity-gain frequency within the whole commonmode input range. Two new methods to control theg _m are introduced. Both operational amplifiers use the same rail-to-rail output stage. The operational amplifiers have been integrated in a CMOS semicustom process with transistor lengths of 10µm. The common-mode input voltage swing extends beyond the positive supply rail by 400 mV and beyond the negative supply rail by 200 mV. The output voltage is able to reach within 130 mV of the supply rails. The output current of the operational amplifiers is 2 mA and the voltage gain is 85 dB. The unity-gain frquency is 165 kHz, which is mainly limited by the relatively long transistor lengths of 10µm. In another process with channel lengths of 2µm, simulation results showed that a unity-gain frequency of 4 MHz can easily be obtained.     

Operational amplifier with 1-V rail-to-rail multipath-driven outputstage

A bipolar operational amplifier (op amp) with a rail-to-rail multipath-driven output stage that operates at supply voltages down to 1 V is presented. The bandwidth of this output stage is as high as possible, viz, equal to that of one of the output transistors, loaded by the output capacitance. The output voltage can reach both supply rails within 100 mV and the output current is ±15 mA. The op amp is designed to be loaded by a 100-pF capacitor and the unity-gain bandwidth is 3.4 MHz at a 60° phase margin. The voltage gain is 117 dB and the CMRR is 100 dB. The frequency behavior of the multipath-driven (MPD) topology has an improved performance when compared to that of previously presented low-voltage output stages. A figure of merit F_M for low-voltage op amps has been defined as the bandwidth-power ratio     

1-V operational amplifier with rail-to-rail input and output ranges

A bipolar operational amplifier (OA) with rail-to-rail input and output ranges which can operate at supply voltages down to 1 V is presented. At this supply voltage, the input offset voltage is typically 1.0 mV in an input common-mode voltage range that extends beyond both supply rails for about 300 mV, with a common-mode rejection ratio (CMRR) between 38 and 100 dB, depending on conditions. The output voltage can reach both supply rails within 100 mV, the output current is limited to ±10 mA, the voltage gain is 100 dB, and the bandwidth is 450 kHz. The die is 2.5×5.5 mm². Qualities such as offset, input-bias current, and CMRR are improved when the supply voltage is increased and the dynamic level shift is autonomically turned off. The OA has been protected against unintentional reversal of the output signal when the inputs are substantially overdriven. The output stage of the circuit consists of two full complementary composite transistors, whose HF characteristics have been improved by internal Miller compensation and linearization of the transconductance     

A curvature-corrected low-voltage bandgap reference

A curvature-corrected bandgap reference that can function at supply voltages as low as 1 V, at a supply current of only 100 μA, is presented. After trimming, this bandgap reference has a temperature coefficient (TC) of ±4 p.p.m./°C. The reference voltage is about 200 mV and it can easily be adjusted to higher values. The temperature range of this circuit is from 0 to 125°C. This bandgap reference is realized using a standard bipolar process with base-diffused resistors     

Integrated 1 V thermal shutdown circuit

A 1 V thermal shutdown circuit for the protection of electronic circuits against undesired power dissipation is presented. The circuit functions as a nonlinear current modifier which cuts the bias current of the main circuit down to zero at temperatures above 130 degrees C. The voltage coefficient is 0.5 degrees C/V and the untrimmed accuracy is 7 degrees C.<>