Low Cost, DC to 150 MHz,

Variable Gain Amplifier

Data Sheet

AD8330

Rev. H

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FEATURES

Fully differential signal path, also used with single-sided signals

Inputs from 0.3 mV to 1 V rms, rail-to-rail outputs

Automatic offset compensation (optional)

Linear-in-dB and linear-in-magnitude gain modes

Inverted gain mode: 50 dB to 0 dB at −30 mV/dB

Constant bandwidth: 150 MHz at all gains

Low noise: 5 nV/√Hz typical at maximum gain

Low distortion: ≤−62 dBc typical

Available in a space-saving, 3 mm × 3 mm LFCSP package

APPLICATIONS

Pre-ADC signal conditioning

75 Ω cable driving adjust

AGC amplifiers

FUNCTIONAL BLOCK DIAGRAM

OPHI

CMOP

OPLO

VMAG

ENBL

VGA CORE

OUTPUT

CONTROL

GAIN INTERFACE

OUTPUT

STAGES

CM AND

OFFSET

CONTROL

OFST CNTR

INHI

INLO

MODE

VDBS

COMM

CMGN

Figure 1.

GENERAL DESCRIPTION

The AD8330 is a wideband variable gain amplifier for applications

requiring a fully differential signal path, low noise, well-defined

gain, and moderately low distortion, from dc to 150 MHz. The

input pins can also be driven from a single-ended source. The

peak differential input is ±2 V, allowing sine wave operation at

1 V rms with generous headroom. The output pins can drive

single-sided loads essentially rail-to-rail. The differential output

resistance is 150 Ω. The output swing is a linear function of the

voltage applied to the VMAG pin that internally defaults to 0.5 V,

providing a peak output of ±2 V. This can be raised to 10 V p-p,

limited by the supply voltage.

The basic gain function is linear-in-dB, controlled by the voltage

applied to Pin VDBS. The gain ranges from 0 dB to 50 dB for

control voltages between 0 V and 1.5 V—a slope of 30 mV/dB.

The gain linearity is typically within ±0.1 dB. By changing the

logic level on Pin MODE, the gain decreases over the same range,

with an opposite slope. A second gain control port is provided

at the VMAG pin and allows the user to vary the numeric gain

from a factor of 0.03 to 10. All the parameters of the AD8330

have low sensitivities to temperature and supply voltages. Using

VMAG, the basic 0 dB to 50 dB range can be repositioned to

any value from 20 dB higher (that is, 20 dB to 70 dB) to at least

30 dB lower (that is, –30 dB to +20 dB) to suit the application,

thereby providing an unprecedented gain range of over 100 dB.

A unique aspect of the AD8330 is that its bandwidth and pulse

response are essentially constant for all gains, over both the

basic 50 dB linear-in-dB range, but also when using the linear-

in-magnitude function. The exceptional stability of the HF

response over the gain range is of particular value in those VGA

applications where it is essential to maintain accurate gain law-

conformance at high frequencies.

An external capacitor at Pin OFST sets the high-pass corner of

an offset reduction loop, whose frequency can be as low as 5 Hz.

When this pin is grounded, the signal path becomes dc-coupled.

When used to drive an ADC, an external common-mode control

voltage at Pin CNTR can be driven to within 0.5 V of either ground

Other features, such as two levels of power-down (fully off and

a hibernate mode), further extend the practical value of this

exceptionally versatile VGA.

The AD8330 is available in 16-lead LFCSP and 16-lead QSOP

packages and is specified for operation from −40°C to +85°C.