AD8352 datasheet(13/20 Pages) AD

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AD8352

Rev. B | Page 13 of 20

This broadband optimization was also performed at 180 MHz.

As with differential input drive, the resulting distortion levels

at lower frequencies are based on the CD and RD specified in

Table 7 and Table 8. As with differential input drive, relative

third-order reduction improvement at frequencies below

140 MHz is realized with proper selection of CD and RD.

–60

–110

FREQUENCY (MHz)

140

190

240

–70

–80

–90

–100

2V p-p OUT

1V p-p OUT

Figure 29. Single-Ended, Third-Order Harmonic Distortion (HD3) vs.

Frequency, 200 Ω Load

–60

–110

FREQUENCY (MHz)

140

190

240

–70

–80

–90

–100

1V p-p OUT

2V p-p OUT

Figure 30. Single-Ended, Second-Order Harmonic Distortion (HD2) vs.

Frequency, 1 kΩ Load

–60

–110

FREQUENCY (MHz)

140

190

240

–70

–80

–90

–100

1V p-p OUT

2V p-p OUT

Figure 31. Single-Ended, Third-Order Harmonic Distortion (HD3) vs.

Frequency, 1 kΩ Load

Table 7. Distortion Cancellation Selection Components

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

AV (dB)

RG (Ω)

CD (pF)

RD (kΩ)

4.3 k

Open

4.3

540

Open

4.3

220

0.1

4.3

120

0.3

4.3

0.6

4.3

0.9

4.3

Table 8. Distortion Cancellation Selection Components

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

AV (dB)

RG (Ω)

CD (pF)

RD (kΩ)

3 k

Open

4.3

470

Open

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 Table 5 and Table 6 were determined for minimizing

broadband, single tone third-order levels.

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 trade-offs.

Figure 32 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 33. These four data points (the

CD value and associated OIP3 levels) are extrapolated to provide

close estimates of OIP3 levels for any specific frequency between

30 MHz and 180 MHz. For frequencies below ~140 MHz, narrow-

band tuning of OIP3 results in relatively higher OIP3s (vs. the

broadband results shown in Table 2 of the specifications). Though

not shown, frequencies below 30 MHz also result in improved

OIP3s when using proper values for CD.

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