AD9864-EBZ datasheet(45/48 Pages) AD

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AD9864

Data Sheet

Rev. A | Page 44 of 47

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

0.1µF

LOSC

RBIAS

COSC

VDDC

IFIN

ATTENUATED PATH WITH

CLIP POINT = 7.0dBm

DIRECT PATH WITH

CLIP POINT = –17dBm

FREF

Figure 75. 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 self biasing inputs of the LO to ground (that is, GNDI), or

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

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

IFIN signal without any frequency translation. The IFIN signal

must be centered around the resonant frequency of the Σ-∆

ADC, 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.

Because the mixer does not have any losses associated with the

mixing 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 76. Applications requiring the highest

instantaneous dynamic range must set the VGA for maximum

attenuation. Several extra decibels in SNR performance can be

gained at lower signal bandwidths by using 24-bit I/Q data.

105

BW (kHz)

120

140

160

100

MIN ATTEN WITH

24-BIT I/Q DATA

MAX ATTEN WITH

16-BIT I/Q DATA

MIN ATTEN WITH

16-BIT I/Q DATA

MAX ATTEN WITH

24-BIT I/Q DATA

fCLK = 18MSPS

Figure 76. Hung Mixer SNR vs. BW and VGA

AD9864-EBZ Datasheet(PDF) 45 Page - Analog Devices

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