ADA4622-1ARJZ-R2 datasheet(27/38 Pages) AD

27 / 38 page

Data Sheet

ADA4622-1/ADA4622-2/ADA4622-4

Rev. E | Page 27 of 38

THEORY OF OPERATION

SLEW

ENHANCEMENT

CIRCUIT

ED1

+IN x

V+

OUT x

V–

–IN x

ED2

R10

OUTPUT

STAGE

VBIAS

OUT1

OUT2

ED3

ED4

ED5

ED6

IMAGIC

CURRENT

CURRENT MIRROR

Figure 80. Simplified Circuit Diagram

INPUT CHARACTERISTICS

The ADA4622-1/ADA4622-2/ADA4622-4 input stage consists

of N-channel JFETs that provide low offset, low noise, and high

impedance. The minimum input common-mode voltage

extends from −0.2 mV below V− to 1 V less than V+. Driving

the input closer to the positive rail causes loss of amplifier

bandwidth and increased common-mode voltage error. Figure 81

shows the rounding of the output due to the loss of bandwidth.

The input and output are superimposed.

CH1 1.00V CH2 1.00V

M2.00µs

A CH1

3.00V

Figure 81. Bandwidth Limiting due to Headroom Requirements

The ADA4622-1/ADA4622-2/ADA4622-4 do not exhibit phase

reversal for input voltages up to V+. For input voltages greater

than V+, a 10 kΩ resistor in series with the noninverting input

prevents phase reversal at the expense of higher noise (see

Figure 82).

CH1 1.00V CH2 1.00V

M2.00µs

A CH1

3.84V

Figure 82. No Phase Reversal

Because the input stage uses N-channel JFETs, the input current

during normal operation is negative. However, the input bias

current changes direction as the input voltage approaches V+

due to internal junctions becoming forward-biased (see Figure 83).

–3

–2

–1

–5

–4

–3

–2

–1

COMMON-MODE VOLTAGE (V)

Figure 83. Input Bias Current vs. Common-Mode Voltage with ±5 V Supply

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