AD8352ACPZ-R7 datasheet(11/20 Pages) AD

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AD8352

Rev. A | Page 11 of 20

APPLICATIONS

GAIN AND DISTORTION ADJUSTMENT

(DIFFERENTIAL INPUT)

Table 5 and Table 6 show the required value of RG for the gains

specified at 200 Ω and 1 kΩ loads. Figure 22 and Figure 24 plot

gain vs. RG up to 18 dB for both load conditions. For other

output loads (RL), use Equation 1 to compute gain vs. RG.

ial

VDifferent

⎟

⎠

⎞

⎜

⎝

⎛

430

)

(

)

(

500

(1)

where:

RL = single-ended load.

RG = gain setting resistor.

The third-order harmonic distortion can be reduced by using

external components RD and CD. Table 5 and Table 6 show the

required values for RD and CD 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. CD 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 broadband distortion for the specified frequencies below

and above this value. For applications above approximately

300 MHz, CD and RD are not required. See the Specifications

section and third-order harmonic plots in the Typical

Performance Characteristics section for more details.

CD can be further optimized for narrow-band tuning require-

ments 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 CD,

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 RD can be determined for loads between 200 Ω and 1 kΩ.

For loads above 1 kΩ, use the 1 kΩ RD values listed in Table 6.

Table 5. Broadband Selection of RG, CD, and RD: 200 Ω Load

AV (dB)

RG (Ω)

CD (pF)

RD (kΩ)

390

Open

6.8

220

Open

4.3

140

0.1

4.3

115

0.2

4.3

0.3

4.3

0.6

4.3

Table 6. Broadband Selection of RG, CD, and RD: 1 kΩ Load

AV (dB)

RG (Ω)

CD (pF)

RD (kΩ)

750

Open

6.8

360

Open

6.8

210

Open

6.8

180

0.05

6.8

130

0.1

6.8

0.3

6.8

0.5

6.8

400

RG (Ω)

100

200

300

150

250

350

Figure 22. Gain vs. RG, RL = 200 Ω

CD (pF)

0.2

0.4

0.6

0.8

1.0

0.1

0.3

0.5

0.7

0.9

Figure 23. Gain vs. CD, RL = 200 Ω

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