AD8352
Rev. B | Page 11 of 20
APPLICATIONS INFORMATION
GAIN AND DISTORTION ADJUSTMENT
(DIFFERENTIAL INPUT)
Table 5 and Table 6 show the required value of R
G
for the gains
specified at 200 Ω and 1 kΩ loads. Figure 22 and Figure 24 plot
gain vs. R
G
up to 18 dB for both load conditions. For other output
loads (R
L
), use Equation 1 to compute gain vs. R
G
.
L
L
G
G
alDifferentiV
R
RR
R
A
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+++
+
=
43053)(5)(
500
(1)
where
R
L
is the single-ended load.
R
G
is the gain setting resistor.
The third-order harmonic distortion can be reduced by using
external components R
D
and C
D
. Table 5 and Table 6 show the
required values for R
D
and C
D
for the specified gains to achieve
(single tone) third-order distortion reduction at 180 MHz.
Figure 23 and Figure 25 show any gain (up to 18 dB) vs. C
D
for
200 Ω and 1 kΩ loads, respectively. When these values are selected,
they result in minimum single tone, third-order distortion at
180 MHz. This frequency point provides the best overall broad-
band distortion for the specified frequencies below and above
this value. For applications above ~300 MHz, C
D
and R
D
are
not required. See the Specifications section and the third-order
harmonic plots for more details (see Figure 12, Figure 14, and
Figure 15).
C
D
can be further optimized for narrow-band tuning requirements
below 180 MHz that result in relatively lower third-order (in-
band) intermodulation distortion terms. See the Narrow-Band,
Third-Order Intermodulation Cancellation section for more
information. Though not shown, single tone, third-order
optimization can also be improved for narrow-band frequency
applications below 180 MHz with the proper selection of C
D
,
and 3 dB to 6 dB of relative third-order improvement can be
realized at frequencies below approximately 140 MHz.
Using the information listed in Table 5 and Table 6, an extrapolated
value for R
D
can be determined for loads between 200 Ω and 1 kΩ.
For loads above 1 kΩ, use the 1 kΩ R
D
values listed in Table 6.
Table 5. Broadband Selection of RG, CD, and RD, 200 Ω Load
A
V
(dB) R
G
(Ω) C
D
(pF) R
D
(kΩ)
3 390 Open 6.8
6 220 Open 4.3
9 140 0.1 4.3
10 115 0.2 4.3
12 86 0.3 4.3
15 56 0.6 4.3
18 35 1 4.3
Table 6. Broadband Selection of R
G
, C
D
, and R
D
, 1 kΩ Load
A
V
(dB) R
G
(Ω) C
D
(pF) R
D
(kΩ)
3 750 Open 6.8
6 360 Open 6.8
9 210 Open 6.8
10 180 0.05 6.8
12 130 0.1 6.8
15 82 0.3 6.8
18 54 0.5 6.8
20
0
0 400
R
G
(Ω)
GAIN (dB)
18
16
14
12
10
8
6
4
2
100 200 30050 150 250 350
05728-026
Figure 22. Gain vs. R
G
, R
L
= 200 Ω
20
0
0
C
D
(pF)
GAIN (dB)
18
16
14
12
10
8
6
4
2
0.2 0.4 0.6 0.8 1.00.1 0.3 0.5 0.7 0.9
05728-027
Figure 23. Gain vs. C
D
, R
L
= 200 Ω
