ADL5565-EVALZ(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADL5565-EVALZ Datasheet PDF : 28 Pages
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The single-ended gain can be determined using the following
formula. The values of RG and RX for each gain configuration
are shown in Table 8.
AV1 =
200
× R2 × RX + RS × RL
RG
+
⎜⎜⎝⎛
RS
RS
× R2
+ R2
⎟⎟⎠⎞
RS + R2
RX
10 + RL
(2)
In Equation 2, RG is the gain setting resistor (see Figure 1).
Table 8. Values of RG and RX for Single-Ended Gain
Gain (dB)
RG (Ω)1
RX (Ω)
5.3
100
R2 || 1582
10.3
50
R2 || 962
13
33.5
R2 || 742
1 RG is the gain setting resistor (see Figure 1).
2 These values are based on a 50 Ω input match.
GAIN ADJUSTMENT AND INTERFACING
The effective gain of the ADL5565 can be reduced using a number
of techniques. A matched attenuator network can reduce the
effective gain; however, this requires the addition of a separate
component that can be prohibitive in size and cost. Instead, a
simple voltage divider can be implemented using the combination
of additional series resistors at the amplifier input and the input
impedance of the ADL5565, as shown in Figure 36. A pair of
resistors is used to match to the impedance of the previous stage.
1/2 RS
AC
1/2 RS
1/2 RSHUNT
1/2 RSHUNT
0.1µF 1/2 RSERIES
0.1µF 1/2 RSERIES
VIN1
VIN2
VIP1 ADL5565
VIP2
Figure 36. Gain Adjustment Using a Series Resistor
Figure 36 shows a typical implementation of the divider concept
that effectively reduces the gain by adding attenuation at the
input. For frequencies less than 100 MHz, the input impedance
of the ADL5565 can be modeled as a real 66 Ω, 100 Ω, or 200 Ω
resistance (differential) for maximum, middle, and minimum
gains, respectively. Assuming that the frequency is low enough
to ignore the shunt reactance of the input and high enough so
that the reactance of moderately sized ac coupling capacitors
can be considered negligible, the insertion loss, Il, due to the
shunt divider can be expressed as
Il(dB)
=
20 log⎜⎜⎝⎛
RG
RSERIES +
RG
⎟⎟⎠⎞
(3)
In Equation 3, RG is the gain setting resistor (see Figure 1).
Adjusted Gain (dB) =
6 dB, 12 dB, or 15.5 dB Gain – Il (dB)
(4)
ADL5565
The necessary shunt component, RSHUNT, to match to the source
impedance, RS, can be expressed as
RSHUNT = 1 −
1
1
(5)
RS RSERIES + RG
In Equation 5, RG is the gain setting resistor (see Figure 1).
The insertion loss and the resultant power gain for multiple
shunt resistor values are summarized in Table 9. The source
resistance and input impedance need careful attention when
using Equation 3, Equation 4, and Equation 5. The reactance
of the input impedance of the ADL5565 and the ac coupling
capacitors must be considered before assuming that they make
a negligible contribution.
Table 9. Differential Gain Adjustment Using Series Resistor
Gain Differential
Differential Differential
(dB) RG (Ω)4
RS (Ω) RSERIES (Ω)
RSHUNT (Ω)5
01
200
50
200
57.6
11
200
50
154
57.6
21
200
50
118
59
31
200
50
84.5
60.4
41
200
50
52.3
61.9
51
200
50
24.9
64.9
61
200
50
0
66.5
72
100
50
78.7
69.8
82
100
50
59
73.2
92
100
50
42.2
76.8
102 100
50
26.7
82.5
112 100
50
12.7
88.7
122 100
50
0
100
133 66.7
50
23.7
113
143 66.7
50
13.7
133
15.53 66.7
50
0
200
1 Amplifier is configured for 6 dB gain setting.
2 Amplifier is configured for 12 dB gain setting.
3 Amplifier is configured for 15.5 dB gain setting.
4 RG is the gain setting resistor (see Figure 1).
5 The resistor values are rounded to the nearest real resistor value.
Rev. 0 | Page 19 of 28
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