ADL5565ACPZ-R7 datasheet(19/29 Pages) AD

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Data Sheet

ADL5565

Rev. D | Page 19 of 28

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 9.













200

(2)

In Equation 2, RG is the gain setting resistor (see Figure 1).

Table 9. Values of RG and RX for Single-Ended Gain

Gain (dB)

RG (Ω)1

RX (Ω)

5.3

100

R2 || 1582

10.3

R2 || 962

33.5

R2 || 742

RG is the gain setting resistor (see Figure 1).

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.

0.1µF

1/2 RSHUNT

1/2 RS

0.1

µF 1/

2 RSERIES

VIP1

VIN2

VIN1

VIP2

1/2 RSERIES

1/2 RSHUNT

ADL5565

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













SERIES

log

)

(

(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)

The necessary shunt component, RSHUNT, to match to the source

impedance, RS, can be expressed as

SERIES

SHUNT

−

(5)

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 10. 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 10. Differential Gain Adjustment Using Series Resistor

Gain

(dB)

Differential

RG (Ω)4

RS (Ω)

Differential

RSERIES (Ω)

Differential

RSHUNT (Ω)5

200

57.6

200

154

57.6

200

118

200

84.5

60.4

200

52.3

61.9

200

24.9

64.9

200

66.5

100

78.7

69.8

100

73.2

100

42.2

76.8

102

100

26.7

82.5

112

100

12.7

88.7

122

100

133

66.7

23.7

113

143

66.7

13.7

133

15.53

66.7

200

Amplifier is configured for 6 dB gain setting.

Amplifier is configured for 12 dB gain setting.

Amplifier is configured for 15.5 dB gain setting.

RG is the gain setting resistor (see Figure 1).

The resistor values are rounded to the nearest real resistor value.

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