AD8363ACPZ-R7 datasheet(26/36 Pages) AD

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AD8363

Rev. 0 | Page 26 of 36

CH1 500mV

M 1.00ms

A CH1

600mV

CH1 RISE

81.78µs

CH1 FALL

1.337ms

T 10.00%

Table 5 shows the recommended values of CLPF for popular

modulation schemes. For nonpulsed waveforms, increase CLPF

until the residual output noise falls below 50 mV (±0.5 dB). In

each case, the capacitor can be increased to further reduce the

noise. A 10% to 90% step response to an input step

is also listed. Where the increased response time is unacceptably

high, reduce CLPF, which increases the noise on the output. Due

to the random nature of the output ripple, if it is sampled by

an ADC, averaging in the digital domain further reduces the

residual noise.

Table 5 gives CLPF values to minimize noise while trying to keep

a reasonable response time. For nonpulsed type waveforms,

averaging is not required on the output. For pulsed waveforms,

the smaller the noise, the less averaging is needed on the output.

Figure 62. AD8363 Output to a WiMAX 802.16, 64 QAM, 256 Subcarriers,

10 MHz Bandwidth Signal with CLPF = 0.027 μF

System specifications determine the necessary rise time and fall

time. For example, the suggested CLPF value for WiMAX assumes

that it is not necessary to measure the power in the preamble.

Figure 62 shows how the rise time cuts off the preamble. Note

that the power in the preamble can be easily measured; however,

the CLPF value would have to be reduced slightly, and the noise in

the main signal would increase.

As shown in Figure 61, the fall time for the AD8363 increases

faster than the rise time with an increase in CLPF capacitance.

Some pulse-type modulation standards require a fast fall time as

well as a fast rise time, and in all cases, less output ripple is desired.

Placing an RC filter on the output reduces the ripple, according

to the frequency content of the ripple and the filter’s poles and

zeros. Using an RC output filter also changes the rise and fall

time vs. the output ripple response as compared to increasing

the CLPF capacitance.

Table 5. Recommended CLPF Values for Various Modulation Schemes

Modulation/Standard

Crest Factor (dB)

CLPF

Residual Ripple

(mV p-p)

Response Time (Rise/Fall)

10% to 90%

W-CDMA, 1Carrier, TM1-64

0.1 μF

236 μs/2.9 ms

W-CDMA, 1Carrier, TM1-64 (EVDO)

3900 pF

150

8.5 μs/100 μs

W-CDMA 4Carrier, TM1-64

0.1 μF

240 μs/2.99 ms

CDMA2000, 1Carrier, 9CH

9.1

0.1 μF

210 μs/3.1 ms

CDMA2000, 3Carrier, 9CH

0.1 μF

215 μs/3.14 ms

WiMAX 802.16 , 64 QAM, 256 Subcarriers, 10 MHz Bandwidth

0.027 μF

83 μs/1.35 ms

6C TD-SCDMA

0.01 μF

24 μs/207 μs

1C TD-SCDMA

11.4

0.01 μF

24 μs /198 μs

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