AD8330-EVAL Analog Devices Inc, AD8330-EVAL Datasheet - Page 23

• Manufacturer Part Number: AD8330-EVAL
• Description: BOARD EVAL FOR AD8330
• Manufacturer: Analog Devices Inc

Specifications of AD8330-EVAL

• Rohs Status: RoHS non-compliant

Figure 62 shows typical results for V
input amplitude of 450 mV (the actual combination is not
important), a rise time of 2 ns, and V
upper waveforms, the load capacitors are both zero, and a small
amount of overshoot is visible; with 40 pF, the response is cleaner.
A shunt capacitance of 20 pF from OPHI to OPLO has a similar
effect. Coupling capacitors for this demonstration are suffi-
ciently large to prevent any visible droop over this time scale.
The outputs at the load side eventually assume a mean value of
zero, with negative and positive excursions depending on the
duty cycle.
The bandwidth from Pin VMAG to these outputs is somewhat
higher than from the normal input pins. Thus, when this pin is
used to rapidly modulate the primary signal, some further
experimentation with response optimization may be required.
In general, the AD8330 is very tolerant of a wide range of
loading conditions.
Preserving Absolute Gain
Although the AD8330 is not laser trimmed, its absolute gain
calibration, based mainly on ratios, is very good. Full details are
found in the Specifications section and in the typical performance
curves (see the Typical Performance Characteristics section).
Nevertheless, having finite input and output impedances, the
gain is necessarily dependent on the source and load conditions.
The loss that is incurred when either of these is finite causes an
error in the absolute gain. The absolute gain can also be
uncertain due to the approximately ±20% tolerance in the
absolute value of the input and output impedances.
Often, such losses and uncertainties can be tolerated and
accommodated by a correction to the gain control bias. On the
other hand, the error in the loss can be essentially nulled by
using appropriate modifications to either the source impedance
(R
padding them with series or shunt components).
The formulation for this correction technique was previously
described. However, to simplify its use, Table 5 shows spot
values for combinations of R
that is not dependent on sample-to-sample variations in on chip
S
) or the load impedance (R
–0.2
–0.2
–0.4
–0.6
–0.8
–1.0
–1.2
–0.2
–0.2
–0.4
–0.6
–0.8
–1.0
–1.2
1.2
1.0
0.8
0.6
0.4
0.2
0.2
1.2
1.0
0.8
0.6
0.4
0.2
0.2
0
0
0
0
0
Figure 62. Typical Pulse Response for Figure 61
5ns
10ns
S
and R
L
), or both (in some cases by
15ns
L
DBS
MAG
resulting in an overall loss
= 0.24 V, a square wave
raised to 2.0 V. In the
20ns
25ns
Rev. E | Page 23 of 32
resistances. Furthermore, this fixed and predictable loss can be
corrected by an adjustment to V
Table 5. Preserving Absolute Gain
R
10
15
20
30
50
75
100
150
200
300
500
750
1 k
1.5 k
2 k
Calculation of Noise Figure
The AD8330 noise is a consequence of its intrinsic voltage noise
spectral density (E
(I
V
(R
as follows:
Note that purely resistive source and input impedances as a conces-
sion to simplicity is assumed. A more thorough treatment of
noise mechanisms, for the case where the source is reactive, is
beyond the scope of these brief notes. Also note that V
the voltage noise spectral density appearing across INHI and
INLO, the differential input pins. In preparing for the calculation
of the noise figure, V
voltage across the source, and V
input to the AD8330. The relationship is simply
At maximum gain, E
Thus, the short-circuit voltage noise is
Next, examine the net noise when R
rectly called the matching condition, rather than source impedance
termination, which is the actual situation in this case.
S
NSD
NOISE_IN
I
(Ω)
), nominally 1 kΩ, and the differential source resistance (R
). Their combined effect generates a net input noise,
V
V
V
NOISE
IN
NOISE
5.08 nV/√Hz
, that is a function of the input resistance of the device
=
R
15 k
10 k
7.5 k
5.0 k
3.0 k
2.0 k
1.5 k
1.0 k
750
500
300
200
150
100
75
L
_
(
_
R
(Ω)
V
IN
IN
I
SIG
=
+
=
R
R
I
S
NSD
{
Factor
0.980
0.971
0.961
0.943
0.907
0.865
0.826
0.756
0.694
0.592
0.444
0.327
0.250
0.160
0.111
E
{
)
(
4
NSD
NSD
Uncorrected Loss
SIG
) and the current noise spectral density
1 .
is defined as the open-circuit signal
2
n
is 4.1 nV/√Hz, and I
+
/ V
I
NSD
Hz
2
IN
MAG
(
R
dB
0.17
0.26
0.34
0.51
0.85
1.26
1.66
2.43
3.17
4.56
7.04
9.72
12.0
15.9
19.1
) (
2
is defined as the differential
I
+
, as indicated in Table 5.
+
S
= R
R
3
S
pA
)
I
2
}
= 1 kΩ, often incor-
/
V
Correct Loss
0.510
0.515
0.520
0.530
0.551
0.578
0.605
0.661
0.720
0.845
1.125
1.531
2.000
3.125
4.500
NSD
Hz
MAG
is 3 pA/√Hz.
)
Required to
2
(
1
AD8330
k
Ω
NOISE_IN
+
0
)
2
(16)
(17)
(18)
}
S
is
)
=