CLASS AB CONTROL

OUT

InP

InM

LMV601, LMV602, LMV604

SNOSC70B – APRIL 2012 – REVISED MARCH 2013

www.ti.com

APPLICATION SECTION

LMV601/LMV602/LMV604

The LMV601/LMV602/LMV604 family of amplifiers features low voltage, low power, and rail-to-rail output

operational amplifiers designed for low voltage portable applications. The family is designed using all CMOS

technology. This results in an ultra low input bias current. The LMV601 has a shutdown option, which can be

used in portable devices to increase battery life.

A simplified schematic of the LMV601/LMV602/LMV604 family of amplifiers is shown in Figure 44. The PMOS

input differential pair allows the input to include ground. The output of this differential pair is connected to the

Class AB turnaround stage. This Class AB turnaround has a lower quiescent current, compared to regular

turnaround stages. This results in lower offset, noise, and power dissipation, while slew rate equals that of a

conventional turnaround stage. The output of the Class AB turnaround stage provides gate voltage to the

complementary common-source transistors at the output stage. These transistors enable the device to have rail-

to-rail output.

Figure 44. Simplified Schematic

CLASS AB TURNAROUND STAGE AMPLIFIER

This patented folded cascode stage has a combined class AB amplifier stage, which replaces the conventional

folded cascode stage. Therefore, the class AB folded cascode stage runs at a much lower quiescent current

compared to conventional folded cascode stages. This results in significantly smaller offset and noise

contributions. The reduced offset and noise contributions in turn reduce the offset voltage level and the voltage

noise level at the input of the LMV601/LMV602/LMV604. Also the lower quiescent current results in a high open-

loop gain for the amplifier. The lower quiescent current does not affect the slew rate of the amplifier nor its ability

to handle the total current swing coming from the input stage.

The input voltage noise of the device at low frequencies, below 1kHz, is slightly higher than devices with a BJT

input stage; However the PMOS input stage results in a much lower input bias current and the input voltage

noise drops at frequencies above 1kHz.

SAMPLE AND HOLD CIRCUIT

The lower input bias current of the LMV601 results in a very high input impedance. The output impedance when

the device is in shutdown mode is quite high. These high impedances, along with the ability of the shutdown pin

to be derived from a separate power source, make LMV601 a good choice for sample and hold circuits. The

sample clock should be connected to the shutdown pin of the amplifier to rapidly turn the device on or off.

14

Submit Documentation Feedback

Copyright © 2012–2013, Texas Instruments Incorporated

Product Folder Links: LMV601 LMV602 LMV604