AFE5808A datasheet(40/66 Pages) TI1

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Sum Amp

with LPF

LNA1

Voltage to

Current

Converter

Sum Amp

with LPF

I-CH

Q-CH

I-CLK

Q-CLK

LNA8

Voltage to

Current

Converter

I-CH

Q-CH

I-CLK

Q-CLK

I-CH

Q-CH

Clock

Distribution

Circuits

1×

fcw CLK

N×

fcw CLK

AFE5808A

SLOS729B – OCTOBER 2011 – REVISED APRIL 2012

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CONTINUOUS-WAVE (CW) BEAMFORMER

Continuous-wave Doppler is a key function in mid-end to high-end ultrasound systems. Compared to the TGC

mode, the CW path needs to handle high dynamic range along with strict phase noise performance. CW

beamforming is often implemented in analog domain due to the mentioned strict requirements. Multiple

beamforming methods are being implemented in ultrasound systems, including passive delay line, active mixer,

and passive mixer. Among all of them, the passive mixer approach achieves optimized power and noise. It

satisfies the CW processing requirements, such as wide dynamic range, low phase noise, accurate gain and

phase matching.

A simplified CW path block diagram and an In-phase or Quadrature (I/Q) channel block diagram are illustrated

below respectively. Each CW channel includes a LNA, a voltage-to-current converter, a switch-based mixer, a

shared summing amplifier with a low-pass filter, and clocking circuits. All blocks include well-matched in-phase

and quadrature channels to achieve good image frequency rejection as well as beamforming accuracy. As a

result, the image rejection ratio from an I/Q channel is better than -46dBc which is desired in ultrasound systems.

Figure 69. Simplified Block Diagram of CW Path

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