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AD8330
*
Low Cost DC-150 MHz
Variable Gain Amplifier
Tel: 781/329-4700 Fax: 781/326-8703
www.analog.com*
Protected by U.S.Patent No. 5,969,657; other patents pending.
FUNCTIONAL BLOCK DIAGRAM
COMM
OPHI
INLO
OPLO
INHI
VPSI
VPSO
CMOP
MODE
VDBS
CMGN
VMAG
OFST
ENBL
CNTR
VPOS
BIAS AND V
REF
GAIN INTERFACE
CM AND
OFFSET
CONTROL
OUTPUT
STAGES
OUTPUT
CONTROL
VGA CORE
12
11
10
9
16
15
14
13
5
6
7
8
1
2
3
4
FREQUENCY – Hz
90
100k
G
30
–10
–50
50
10
–30
1M
10M
100M
300M
70
Figure 1. AC Response over the Extended Gain Range
FEATURES
Fully Differential Signal Path
May also be Used with Single-Sided Signals
Inputs from 0.3 mV to 1 V rms, Rail-Rail Outputs
Differential R
IN
= 1 k
; R
OUT
(Each Output) 75
Automatic Offset Compensation (Optional)
Linear-in-dB and Linear-in-Magnitude Gain Modes
0 dB to 50 dB, for 0 V < V
DBS
< 1.5 V (30 mV/dB)
Inverted Gain Mode: 50 dB to 0 dB at
–
30 mV/dB
0.03 to 10 Nominal Gain for 15 mV < V
MAG
< 5 V
Constant Bandwidth: 150 MHz at All Gains
Low Noise: 5 nV/
√
Hz
typical at Maximum Gain
Low Distortion:
≤
–
62 dBc Typ
Low Power: 20 mA Typ at V
S
of 2.7 V
–
6 V
Available in Space Saving 3 3 LFCSP Package
APPLICATIONS
Pre-ADC Signal Conditioning
75
Cable Driving Adjust
AGC Amplifiers
GENERAL DESCRIPTION
The AD8330 is a wideband variable-gain amplifier for use in
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 sinewave operation at
1 V rms with generous headroom. The output pins can optionally
drive single-sided loads and each swing essentially rail-to-rail.
The differential output resistance is 150
. The output swing is
a linear function of the voltage applied to the VMAG pin, which
internally defaults to 0.5 V, to provide a peak output of
±
2 V.
This may 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 will decrease over the same
range, with opposite slope. A second gain control port is provided
at pin VMAG 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 V
MAG
, 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, 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, not only over 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 may 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 V
S
to accommodate a wide variety of requirements. By
default, the two outputs are positioned at the mid point of the
supply, V
S
/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 a 16-lead LFCSP and 16-lead QSOP
packages and is specified for operation from
–
40
°
C to +85
°
C.