14-Bit, 40 MSPS/65 MSPS

Analog-to-Digital Converter

AD6644

Rev. D

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FEATURES

65 MSPS guaranteed sample rate

40 MSPS version available

Sampling jitter < 300 fs

100 dB multitone SFDR

1.3 W power dissipation

Differential analog inputs

Pin compatible to AD6645

Twos complement digital output format

3.3 V CMOS compatible

Data-ready for output latching

APPLICATIONS

Multichannel, multimode receivers

AMPS, IS-136, CDMA, GSM, WCDMA

Single channel digital receivers

Antenna array processing

Communications instrumentation

Radar, infrared imaging

Instrumentation

GENERAL DESCRIPTION

The AD6644 is a high speed, high performance, monolithic 14-bit

analog-to-digital converter (ADC). All necessary functions,

including track-and-hold (TH) and reference, are included on-

chip to provide a complete conversion solution. The AD6644

provides CMOS-compatible digital outputs. It is the third

generation in a wideband ADC family, preceded by the AD9042

(12-bit 41 MSPS) and the AD6640 (12-bit 65 MSPS, IF

sampling).

Designed for multichannel, multimode receivers, the AD6644

is part of the Analog Devices, Inc. new SoftCell® transceiver

chipset. The AD6644 achieves 100 dB multitone, spurious-free

dynamic range (SFDR) through the Nyquist band. This break-

through performance eases the burden placed on multimode

digital receivers (software radios) which are typically limited by

the ADC. Noise performance is exceptional; typical signal-to-

noise ratio is 74 dB.

The AD6644 is also useful in single channel digital receivers

designed for use in wide-channel bandwidth systems (CDMA,

WCDMA). With oversampling, harmonics can be placed

outside the analysis bandwidth. Oversampling also facilitates

the use of decimation receivers (such as the AD6620), allowing

the noise floor in the analysis bandwidth to be reduced. By

replacing traditional analog filters with predictable digital

components, modern receivers can be built using fewer RF

components, resulting in decreased manufacturing costs, higher

manufacturing yields, and improved reliability.

The AD6644 is built on the Analog Devices high speed

complementary bipolar process (XFCB) and uses an innovative,

multipass circuit architecture. Units are packaged in a 52-lead

plastic low profile quad flat package (LQFP) specified from –

25°C to +85°C.

PRODUCT HIGHLIGHTS

1. Guaranteed sample rate is 65 MSPS.

2. Fully differential analog input stage.

3. Digital outputs can be run on 3.3 V supply for easy interface

to digital ASICs.

4. Complete solution: reference and track-and-hold.

5. Packaged in small, surface-mount, plastic, 52-lead LQFP.

FUNCTIONAL BLOCK DIAGRAM

5

6

5

AD6644

AIN

AIN

ENCODE

ENCODE

GND

DMID OVR DRY D13

(MSB)

D12 D11 D10 D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

(LSB)

ADC3

TH5

TH4

DAC2

ADC2

TH3

A2

DAC1

DIGITAL ERROR CORRECTION LOGIC

TH2

ADC1

TH1

A1

2.4V

INTERNAL

TIMING

Figure 1.