AD8432ACPZ-R7 datasheet(20/32 Pages) AD

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AD8432

Data Sheet

Rev. D | Page 20 of 32

100

RS (Ω)

(SIMULATED RESULTS)

ACTIVE IMPEDANCE

MATCH

UNTERMINATED

RESISTIVE TERMINATION

(RS = RIN)

Figure 67. Noise Figure vs. RS for Resistive, Active Match, and

Unterminated Inputs

100

RS (Ω)

(SIMULATED RESULTS)

RIN = UNTERMINATED

RIN = 50Ω

RIN = 75Ω

RIN = 100Ω

RIN = 200Ω

RIN = 1kΩ

Figure 68. Noise Figure vs. RS for Various Values of RIN, Actively Matched

The user must determine the level of matching accuracy desired

and adjust RFB accordingly. The RFB and CFB network presents a

load to OPL that OPH does not see. The user can add an identical

load on OPH to improve slightly the distortion caused by this

imbalance.

There is a feedback capacitor (CFB) in series with RFB (see

Figure 65) because the dc levels of the positive output and the

positive input are different. At higher frequencies, the value

of the feedback capacitor must be considered.

The unterminated bandwidth (RFB = ∞) is 200 MHz. The AD8432

has a low input-referred voltage noise of 0.85 nV/√Hz at the

lowest gain, 12.04 dB (unterminated configuration). To achieve

such low noise, the dual amplifier consumes 24 mA, resulting in

a power consumption of 120 mW.

Table 6. Feedback Resistance for Several RIN and Gain Combinations

Desired RIN (Ω)

Differential Gain (V/V)

Single-Ended Gain,

G/2 (V/V)

Exact RFB (Ω),

Equation 2

RFB (Ω), 1% Standard Value

Actual RIN (Ω),

Equation 2

151.2

150

49.6

227.8

226

74.4

100

304.9

301

98.7

200

620

619

199.7

1 k

3.58 k

3.57 k

998.4

252

250

49.6

100

508.2

511

100.5

352.9

357

50.6

100

711.5

715

100.5

453.7

453

49.9

100

914.8

909

99.4

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