AD8330 Analog Devices, AD8330 Datasheet - Page 17

• Manufacturer Part Number: AD8330
• Description: Low Cost DC-150MHz Variable Gain Amplifier
• Manufacturer: Analog Devices

Figure 10. Noise Figure for Source Resistance of 50
5 k , at f = 10 MHz (lower) and 100 MHz (Simulation)
Figure 11. Dynamic Range in dB/ Hz vs. V
1 V rms output) Compared with a Representative X-AMP
(Simulation)
Dynamic Range
The ratio of peak output swing, expressed in rms terms, to the
output-referred noise-spectral-density provides a measure of
dynamic range, in dB/ Hz. For a certain class of variable-gain
amplifiers, exemplified by Analog Devices’ X-AMP family, the
dynamic range is essentially independent of the gain setting,
because the peak output swing and noise are both constant. The
AD8330 provides a different dynamic-range profile, since there
is no longer a constant relationship between these two param-
eters. Figure 11 compares the dynamic range of the AD8330 to
a representative X-AMP.
Input Common-Mode Range and Rejection Ratio
The inputs INHI and INLO should be ac-coupled in most applica-
tions, to achieve the stated noise performance. When direct coupling
is used, care must be taken in setting the dc voltage level at these
inputs, in general, and particularly when minimizing noise is
critical. This objective is complicated by the fact that the common-
mode level varies with the basic gain voltage VDBS. Figure 12
shows this relationship for a supply voltage of 5 V, for tempera-
tures of –35 C, +25 C and +85 C. Figure 13 shows the input
noise-spectral-density (R
voltage, for V
that there is a broad range over which the noise is unaffected by
this dc level. The input CMRR is excellent (see TPC 13).
REV. A
144
140
136
132
128
124
120
116
15
14
13
12
11
10
9
8
7
6
5
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
X-AMP WITH 40dB
OF GAIN AND AN
INPUT NSD
OF nV/ Hz
DBS
= 0.5, 0.6 V, 0.75 V, and 1.5 V. It is apparent
100
S
= 0) versus the input common-mode
R
V
S
DBS
–
–
CONSTANT 1V rms
OUTPUT, BOTH CASES
V
1000
DBS
(V
MAG
= 0.5 V,
10k
to
–17–
Output Noise and Peak Swing
The output noise of the AD8330 is the input noise multiplied by
the overall gain, which includes any optional change to the voltage
V
proportional to this voltage, which, at low gains and high values
of V
as follows:
For example, using a reduced value of V
lowers all gain values by 6 dB, the peak output swing is 1 V
(differentially) and the output noise spectral density evaluates to
102.5 nV/ Hz. The peak output swing is no different at full gain,
but the noise is now
for R
5 nV/ Hz. The output noise for very small values of V
(at or below 15 mV) is not precise, partly because the small input
offset associated with this interface has a large effect on the gain.
MAG
MAG
V
V
V
S
Figure 12. Common-Mode Voltage at Input Pins
vs. V
Figure 13. Input Noise vs. Common-Mode Input
Voltage for V
applied to pin VMAG. The peak output swing is also
OUT_PK
NOISE_OUT
NOISE_OUT
= 0 and V
, will affect the output noise. The scaling for V
26
24
22
20
18
16
14
12
10
3.2
3.1
3.0
2.9
2.8
2.7
2.6
8
6
4
0
0
DBS
0.4
SIMULATION
, for V
0.2
DBS
0.8
COMMON-MODE VOLTAGE AT INHI, INLO – V
4 V
= 1.5 V, assuming an input noise of
DBS
85 70 V
0 1 0 32
1.2
S
MAG
0.4
.
= 5 V, T = –35 C, +25 C, and +85 C
= 0.5 V, 0.6 V, 0.75 V, and 1.5 V
1.6
0.6
.
2.0
MAG
V
V
DBS
2.4
MAG
0.8
2.8
nV
V
1.0
/
3.2
MAG
V
T = +85 C
T = –40 C
T = +25 C
/
Hz
V
V
V
V
DBS
3.6
DBS
DBS
DBS
1.2
= 0.25 V, which
Hz
= 0.75V
AD8330
= 0.5V
= 0.6V
= 1.5V
4.0
1.4
4.4
MAG
DBS
4.8
1.6
= 0 is
(10)
(8)
(9)