AD8285CP-EBZ datasheet(14/27 Pages) AD

14 / 27 page

AD8285

Data Sheet

Rev. B | Page 14 of 27

THEORY OF OPERATION

RADAR RECEIVE PATH AFE

The primary application for the AD8285 is a high speed ramp,

frequency modulated, continuous wave radar (HSR-FMCW radar).

Figure 24 shows a simplified block diagram of an HSR-FMCW

radar system. The signal chain requires multiple channels, each

including a LNA, a PGA, an AAF, and an ADC with a 12-bit

parallel output. The AD8285 provides all of these key components

in a single 10 × 10 LFCSP package.

The performance of each component is designed to meet the

demands of an HSR-FMCW radar system. Some examples of

these performance metrics are the LNA noise, PGA gain range,

AAF cutoff characteristics, and ADC sample rate and resolution.

The AD8285 includes a multiplexer (mux) in front of the ADC

as a cost saving alternative to having an ADC for each channel.

The mux automatically switches between each active channel

after each ADC sample. The DSYNC output indicates when

Channel A data is at the ADC output and when data for each

active channel follows sequentially with each clock cycle.

The effective sample rate for each channel is reduced by a factor

equal to the number of active channels. The ADC resolution of

12 bits with up to 72 MSPS sampling satisfies the requirements

for most HSR-FMCW approaches.

Figure 24. Simplified Block Diagram of a Single Channel

Figure 25. Radar System Overview

MUX

AD8285

MUX

CONTROLLER

SPI

INTERFACE

SDIO

SCLK

AAF

PGA

LNA

PIPELINE

ADC

THIRD-ORDER

ELLIPTICAL FILTER

–6dB,

0dB,

6dB,

12dB

12-BIT

72MSPS

INx+

INx–

22dB

200Ω/

200kΩ

PARALLEL

3.3V CMOS

D11 TO D0

DSYNC

DSP

ANTENNA

VCO

12-BIT

ADC

AAF

PGA

LNA

PGA

LNA

PGA

LNA

AD8285

MUX

REF.

OSCILLATOR

CHIRP RAMP

GENERATOR

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