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 linearin-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 lawconformance
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
or VS to accommodate a wide variety of requirements. By default,
the two outputs are positioned at the midpoint of the supply, VS/2.
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.
Applications
- Pre-ADC signal conditioning
- 75 Ω cable driving adjust
- AGC amplifiers
