CLC5526

Digital Variable Gain Amplifier (DVGA)

General Description

The CLC5526 is a high performance, digitally controlled,

variable-gain amplifier (DVGA). It has been designed for use

in a broad range of mixed signal and digital communication

applications such as mobile radio, cellular base stations and

back-channel modems where automatic-gain-control (AGC)

is required to increase system dynamic range.

The CLC5526 has differential input and output, allowing

large signal swings on a single 5V rail. The input impedance

is 200

Ω. The differential output impedance is 600Ω and is

designed to drivea1k

Ω differential load. The output ampli-

fier

has

excellent

intermodulation

performance.

The

CLC5526 is designed to accept signals from RF elements

and maintain a terminated impedance environment.

The CLC5526 maintains a 350 MHz bandwidth over its en-

tire gain and attenuation range from +30 dB to −12 dB. Inter-

nal clamping ensures very fast overdrive recovery. Two tone

intermodulation distortion is excellent: at 150 MHz, 1 V

−64 dBc.

Input signals to the CLC5526 are scaled by an accurate, dif-

ferential R-2R resistive ladder with an input impedance of

200

Ω. A scaled version of the input is selected under digital

control and passed to the internal amplifier. The input com-

mon mode level is set at 2.4V via a bandgap referenced bias

generator which can be overridden by an external input.

Following the resistive ladder is a fixed, 30 dB gain amplifier.

The output stage common mode voltage of the CLC5526 is

set to 3V, by internal, positive supply connected resistors.

Digital control of the CLC5526 is accomplished by a 3-bit

parallel gain control input and a data valid pin to latch the

data. If the data is not latched, the DVGA is transparent to

gain control updates. All digital inputs are TTL/CMOS com-

patible.

A shutdown input reduces the CLC5526 supply currrent to a

few mA. During shutdown, the input termination is main-

tained and current attenuation settings are held.

The CLC5526 operates over the industrial temperature

range of −40˚C to +85˚C. The part is available in a 20-pin

SSOP package.

Features

n 350 MHz bandwidth

n Differential input and output

n Gain control: parallel w/data latching

n Supply voltage:

+5V

n Supply current:

48 mA

Key Specifications

n Low two tone intermod:

24.5 dBm IP3, 150 MHz

n Low noise:

2.5 nV/

9.3 dB noise figure (max gain)

n Wide gain range:

+30 dB to −12 dB

n Gain step size:

6 dB

Applications

n Cellular/PCS base stations

n IF sampling receivers

n Infrared/CCD imaging

n Back-channel modems

n Electro-optics

n Instrumentation

n Medical imaging

n High definition video

Block Diagram

DS015016-2

June 1999

© 1999 National Semiconductor Corporation

DS015016

www.national.com