ADA4511-2ARMZ-R7 datasheet(20/28 Pages) AD

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Data Sheet

ADA4511-2

THEORY OF OPERATION

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Figure 75. Simplified Schematic

The ADA4511-2 is a dual-channel, low-power, rail-to-rail input

and output, precision complementary metal-oxide semiconductor

(CMOS) op amp that operates over a wide supply voltage range of

6 V to 40 V.

INPUT AND GAIN STAGES

Figure 75 shows the simplified circuit diagram for the ADA4511-2.

The input architecture provides high-impedance, rail-to-rail differ-

ential and common-mode input swing, low noise, low-input bias

current, and low-offset voltage.

An integrated EMI filter increases the signal robustness and helps

prevent EMI signals from coupling into the amplifier. Depending

on the input common-mode voltage, either the negative channel

metal-oxide semiconductor (NMOS) or the positive channel metal-

oxide semiconductor (PMOS) input stage can be active at any time.

The low-offset voltage and low-offset voltage drift specifications are

possible by trimming both the NMOS and PMOS input stages.

The ADA4511-2 includes circuitry that extends the linear input

range, which provides higher slew rates than a traditional input

differential pair and improves the THD. The wide gain bandwidth

product of 10.4 MHz is achieved through internal Miller compensa-

tion.

OUTPUT STAGE

The output of the ADA4511-2 swings rail-to-rail to within 100 mV

of either supply rail. A capacitive load compensation block senses

the load capacitor and adds additional phase margin, if required,

to drive a large capacitor (at least 1 nF) and maintain amplifier

stability.

EMI REJECTION

High-frequency EMI is a threat to precision amplifier performance

in an intended application. Op amps must accurately amplify input

signals despite low signal strength and long transmission lines. All

op amp pins are susceptible to EMI signals. These high-frequency

signals are coupled into an op amp by various means, such as

conduction, near-field radiation, or far-field radiation. For example,

wires and PCB traces act as antennas to pick up high-frequency

EMI signals.

Op amps do not amplify EMI or RF signals due to the relatively low

bandwidth of the amplifier. However, due to the nonlinearities of the

input devices, op amps can rectify these out-of-band signals, which

then appear as a DC offset at the output.

The ADA4511-2 is designed with integrated EMI filters at the

input stage of the op amp. The EMIRR describes the ability of

the ADA4511-2 to perform as intended in the presence of electro-

magnetic energy. The EMIRR is specified for the noninverting pin

in Electrical Specifications. A mathematical method of measuring

EMIRR is defined as follows:

EMIRR=20 log×

∆VIN−PEAK/∆VOS (1)

The EMIRR performance of the ADA4511-2 is shown in Figure 26.

NO PHASE INVERSION

The ADA4511-2 does not suffer from output voltage phase reversal

that occurs in some op amps when the specified input VCM range is

exceeded. Output voltage phase reversal causes the output voltage

to swing to the opposite rail until the input comes back within

the common-mode range. Typically, the inputs of conventional op

amps fail to reach or exceed the common-mode limit toward the

negative range. Phase-reversal is most often associated with junc-

tion field effect transistor (JFET) and/or bipolar field effect transistor

(BiFET) amplifiers, but some bipolar single-supply amplifiers are

also susceptible phase-reversal. The ADA4511-2 guarantees no

phase inversion beyond the entire specified input VCM range all the

way to the absolute maximum input voltage limit.

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