ADL5902 datasheet(22/28 Pages) AD

22 / 28 page

ADL5902

Data Sheet

Rev. B | Page 22 of 28

Figure 48 shows the resulting rise and fall times (signal is pulsed

between off and −10 dBm) with CLPF equal to 10 nF. A 2 kΩ

resistor is placed in series with the VOUT pin, and the capacitance

from this resistor to ground (CFILTER in Figure 47) is varied

up to 1 μF.

100

10k

100k

100

150

200

250

300

100

CFILTER (nF)

RESIDUAL RIPPLE (V p-p)

10% TO 90% RISE TIME (µs)

90% TO 10% FALL TIME (µs)

Figure 48. Residual Ripple, Rise and Fall Times Using an RC Low-Pass Filter

at VOUT, PIN = 0 dBm at 2.14 GHz

For large values of CFILTER, the fall time is dramatically reduced

compared to Figure 46. This comes at the expense of a moderate

increase in rise time.

As CFILTER is reduced, the fall time flattens out. This is because

the fall time is now dominated by the 10 nF CLPF which is

present throughout the measurement.

Table 6 shows recommended minimum values of CLPF for

popular modulation schemes, using just a single filter capacitor

at the CLPF pin. Using lower capacitor values results in rms

measurement errors. Output response time (10% to 90%) is also

shown. If the output noise shown in Table 6 is unacceptably

high, it can be reduced by



Increasing CLPF



Adding an RC filter at VOUT, as shown in Figure 47



Implementing an averaging algorithm after the ADL5902

output voltage is digitized by an ADC

Table 6. Recommended Minimum CLPF Values for Various Modulation Schemes

Modulation/Standard

Peak-Envelope

Power

Signal

Bandwidth

CLPF (min)

Output Noise

Rise/Fall Time (10% to 90%)

W-CDMA, One-Carrier, TM1-64

10.56 dB

3.84 MHz

10 nF

95 mV p-p

12/330

s

W-CDMA Four-Carrier, TM1-64, TM1-32,

TM1-16, TM1-8

12.08 dB

18.84 MHz

5.6 nF

164 mV p-p

7/200

s

LTE, TM1 1CR 20 MHz (2048 Subcarriers,

QPSK Subcarrier Modulation)

11.58 dB

20 MHz

1000 pF

452 mV p-p

1.3/38

s

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