AD9864 datasheet(41/44 Pages) AD

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AD9864

Rev. 0 | Page 41 of 44

VCO

LNA

MIXER

IF SAW 1I

F SAW 2

DUPLEXER PRESELECT

GAIN = –2dB

NF = 2dB

GAIN = 22dB

NF = 1dB

GAIN = –3dB

NF = 3dB

GAIN = 5dB

NF = 12dB

AMP

GAIN = –9dB

NF = –9dB

GAIN = 15dB

NF = 2dB

13MHz

DSP

ASIC

36dB

PAD

SYNCB

DOUTA

CLKOUT

CLKP

CLKN

LOP

LON

AD9864

MASTER

LOOP

FILTER

LOP

LON

IFIN

AD9864

SLAVE

DOUTA

CLKOUT

SYNCB

CLKP

CLKN

IOUTL

LOOP

FILTER

CVAR

0.1

µF

LOSC

RBIAS

COSC

VDDC

IFIN

ATTENUATED PATH WITH

CLIP POINT = 7.0dBm

DIRECT PATH WITH

CLIP POINT = –17dBm

FREF

Figure 73. Example of Split Path Rx Architecture to Increase Receiver Dynamic Range Capabilities

Hung Mixer Mode

The AD9864 can operate in hung mixer mode by tying one of

the LO’s self-biasing inputs to ground, i.e., GNDI, or the

positive supply (VDDI). In this mode, the AD9864 acts as a

narrow-band, band-pass Σ-∆ ADC, since its mixer passes the

IFIN signal without any frequency translation. The IFIN signal

must be centered about the resonant frequency of the Σ-∆ ADC

(i.e., fCLK/8) and the clock rate, fCLK, and decimation factors must

be selected to accommodate the bandwidth of the desired input

signal. Note that the LO synthesizer can be disabled because it

is no longer required.

Since the mixer does not have any losses associated with the mix-

ing operation, the conversion gain through the LNA and mixer is

higher resulting in a nominal input clip point of –24 dBm. The

SNR performance is dependent on the VGA attenuation setting,

I/Q data resolution, and output bandwidth as shown in Figure 74.

Applications requiring the highest instantaneous dynamic range

should set the VGA for maximum attenuation. Also, several extra

decibels in SNR performance can be gained at lower signal band-

widths by using 24-bit I/Q data.

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