ADA4522-4ARZ-R7 datasheet(21/32 Pages) AD

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Data Sheet

ADA4522-1/ADA4522-2/ADA4522-4

Rev. E | Page 21 of 32

THEORY OF OPERATION

The ADA4522-1/ADA4522-2/ADA4522-4 are single, dual, and

quad, ultralow noise, high voltage, zero drift, rail-to-rail output

operational amplifiers. They feature a chopping technique that

offers an ultralow input offset voltage of 5 µV and an input

offset voltage drift of 22 nV/°C maximum for theADA4522-1 and

ADA4522-2 and 25 nV/°C maximum for the ADA4522-4. Offset

voltage errors due to common-mode voltage swings and power

supply variations are also corrected by the chopping technique,

resulting in a superb typical CMRR figure of 160 dB and a

PSRR figure of 160 dB at a 30 V supply voltage.

The ADA4522-1/ADA4522-2/ADA4522-4 have wide operating

voltages from ±2.25 V (or 4.5 V) to ±27.5 V (or 55 V). The

devices are single supply amplifiers, where their input voltage

range includes the lower supply rail. They also offer low voltage

noise density of 5.8 nV/√Hz (at f = 1 kHz, AV = 100) and reduced

1/f noise component. These features are ideal for the amplifica-

tion of low level signals in high precision applications. A few

examples of such applications are weigh scales, high precision

current sensing, high voltage buffers, and signal conditioning

for temperature sensors, among others.

Figure 71 shows the ADA4522-1/ADA4522-2/ADA4522-4

architecture block diagram. The architecture consists of an

input EMI filter and clamp circuitry, three gain stages (Gm1, Gm2,

and Gm3), input and output chopping networks (CHOPIN and

CHOPOUT), a clock generator, offset and ripple correction loop

circuitry, frequency compensation capacitors (C1, C2, and C3),

and thermal shutdown circuitry.

An EMI filter and clamp circuit is implemented at the input

front end to protect the internal circuitry against electrostatic

discharge (ESD) stresses and high voltage transients. The ability

of the amplifier to reject EMI is explained in detail in the EMI

Rejection Ratio section.

CHOPIN and CHOPOUT are controlled by a clock generator and

operate at 4.8 MHz. The input baseband signal is initially

modulated by CHOPIN. Next, CHOPOUT demodulates the input

signal and modulates the millivolt level input offset voltage and

1/f noise of the input transconductance amplifier, Gm1, to the

chopping frequency at 4.8 MHz. The chopping networks remove

the low frequency errors, but, in return, the networks introduce

chopping artifacts at the chopping frequency. Therefore, a offset

and ripple correction loop, operating at 800 kHz, is used. This

frequency is the switching frequency of the amplifier. This

circuitry reduces chopping artifacts, allowing the ADA4522-1/

ADA4522-2/ADA4522-4 to have a high chopping frequency

with minimal artifacts.

The thermal shutdown circuit shuts down the circuit when

the die is overheated (see the Thermal Shutdown section for

more information).

Gm1

Gm2

Gm3

EMI

FILTER

AND

CLAMP

THERMAL

SHUTDOWN

OFFSET

AND RIPPLE

CORRECTION

LOOP

+IN x

–IN x

CHOPIN

CHOPOUT

OUT

4.8MHz CLOCKS

800kHz CLOCKS

CLOCK

GENERATOR

NOTES

1. THE INPUTS ARE +IN x/–IN x ON THE ADA4522-2 AND ADA4522-4,

AND +IN/–IN ON THE ADA4522-1.

2. THE OUTPUT IS OUT ON THE ADA4522-1 AND OUT x ON THE

ADA4522-2 AND ADA4522-4.

Figure 71. ADA4522-1/ADA4522-2/ADA4522-4 Architecture Block Diagram

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