AD8352 datasheet(13/20 Pages) AD

13 / 20 page

AD8352

Rev. 0 | Page 13 of 20

Table 9. Distortion Cancellation Selection Components

(RD and CD) for Required Gain, 1 kΩ Load

–60

–110

FREQUENCY (MHz)

140

190

240

–70

–80

–90

–100

3RDS, 2V p-p OUT

3RDS, 1V p-p OUT

AV (dB)

RG (Ω)

CD (pF)

RD (kΩ)

3 k

0 (DNP)

4.3

470

0 (DNP)

4.3

210

0.2

4.3

120

0.3

4.3

0.5

4.3

NARROW-BAND, THIRD-ORDER

INTERMODULATION CANCELLATION

Broadband, single tone, third-order harmonic optimization

does not necessarily result in optimum (minimum) two tone,

third-order intermodulation levels. The specified values for CD

and RD in

Figure 27. Single-Ended, Third-Order Harmonic Distortion, 200 Ω Load

Table 6 and Table 7 were determined for minimizing

broadband single tone, third-order levels.

–60

–110

FREQUENCY (MHz)

140

190

240

–70

–80

–90

–100

2NDS, 1V p-p OUT

2NDS, 2V p-p OUT

Due to phase-related distortion coefficients, optimizing single

tone, third-order distortion does not result in optimum in band

(2f1 − f2 and 2f2 − f1), third-order distortion levels. By proper

selection of CD (using a fixed 4.3 kΩ RD), IP3s of better than

45 dBm are achieved. This results in degraded out-of-band,

third-order frequencies (f2 + 2f1, f1 + 2f2, 3f1 and 3f2). Thus,

careful frequency planning is required to determine the

tradeoffs.

Figure 30 shows narrow band (2 MHz spacing) OIP3 levels

optimized at 32 MHz, 70 MHz, 100 MHz, and 180 MHz using

the CD values specified in Figure 31. These four data points (the

CD value and associated IP3 levels) are extrapolated to provide

close estimates of IP3 levels for any specific frequency between

30 MHz and 180 MHz. For frequencies below approximately

140 MHz, narrow-band tuning of IP3 results in relatively higher

IP3s (vs. the broadband results shown in

Figure 28. Single-Ended, Second-Order Harmonic Distortion, 1 kΩ Load

–60

–110

FREQUENCY (MHz)

140

190

240

–70

–80

–90

–100

3RDS, 1V p-p OUT

3RDS, 2V p-p OUT

Table 2 specifications).

Though not shown, frequencies below 30 MHz also result in

improved IP3s when using proper values for CD.

200

FREQUENCY (MHz)

100

150

6db

10db

15db

18dB

AV =

RL = 200Ω

RD =4.3kΩ

CD =0.3pF

Figure 29. Single-Ended, Third-Order Harmonic Distortion, 1 kΩ Load

Table 8. Distortion Cancellation Selection Components

(RD and CD) for Required Gain, 200 Ω Load

AV (dB)

RG (Ω)

CD (pF)

RD (kΩ)

4.3 k

0 (DNP)

4.3

540

0 (DNP)

4.3

Figure 30. Third-Order Intermodulation Distortion vs. Frequency for

Various Gain Settings

220

0.1

4.3

120

0.3

4.3

0.6

4.3

0.9

4.3

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