ANALOG DEVICES AD8432 Service Manual

Dual-Channel Ultralow Noise Amplifier with

AD8432

BIAS

ENB COMM

INH1 IND1

INL1

INH2 IND2

INL2

VPS1 VPS2

OPH1 OPL1

GMH1 GO

H1 GOL1 GML1

OPH2 OPL2

GMH2 GOH2 GOL2 GML2

LNA1

LNA2

AD8432

08341-001

FEATURES

Low noise

Input voltage noise: 0.85 nV/√Hz Current noise: 2.0 pA/√Hz

High speed

200 MHz bandwidth (G = 12.04 dB) 295 V/µs slew rate

Selectable gain

G = 12.04 dB (×4) G = 18.06 dB (×8) G = 21.58 dB (×12)

G = 24.08 dB (×16) Active input impedance matching Integrated input clamp diodes Single-ended input, differential output Supply range: 4.5 V to 5.5 V Low power: 60 mW/channel

APPLICATIONS

CW Doppler ultrasound front ends Low noise preamplification Predriver for I/Q demodulators and phase shifters Wideband analog-to-digital drivers

Selectable Gain and Input Impedance

FUNCTIONAL BLOCK DIAGRAM

Figure 1.

GENERAL DESCRIPTION

The AD8432 is a dual-channel, low power, ultralow noise amplifier with selectable gain and active impedance matching. Each channel has a single-ended input, differential output, and integrated input clamps. By pin strapping the gain setting pins, four accurate gains of G = 12.04 dB, 18.06 dB, 21.58 dB, and 24.08 dB (×4, ×8, ×12, and ×16, respectively) are possible. A bandwidth of 200 MHz at G = 12.04 dB makes this amplifier well suited for many high speed applications.

The exceptional noise performance of the AD8432 is made possible by the active impedance matching. Using a feedback network, the input impedance of the amplifiers can be adjusted to match the signal source impedance without compromising the noise performance. Impedance matching and low noise in the AD8432 allow designers to create wider dynamic range systems that are able to detect even very low level signals.

Rev. B

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The AD8432 achieves 0.85 nV/√Hz input-referred voltage noise for a gain of 12.04 dB. The AD8432’s ultralow noise, low distortion, gain accuracy, and channel-to-channel matching are ideal for high performance ultrasound systems and for processing I/Q demodulator signals.

The AD8432 operates on a single supply of 5 V at 24 mA. It is available in a 4 mm × 4 mm, 24-lead LFSCP. The LFCSP features an exposed paddle that provides a low thermal resistance path to the PCB, which enables more efficient heat transfer and increases reliability. The operating temperature range is −40°C to +85°C.

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