ADL5902ACPZ-R7 datasheet(21/28 Pages) AD

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Data Sheet

ADL5902

Rev. B | Page 21 of 28

Figure 46 shows how output noise varies with CLPF when the

ADL5902 is driven by a single-carrier W-CDMA signal (Test

Model TM1-64, peak envelope power = 10.56 dB, bandwidth =

3.84 MHz). With a 10 μF capacitor on CLPF, there is residual

noise on VOUT of 4.4 mV p-p, which is less than 0.1 dB error

(assuming a slope of approximately 53 mV/dB).

100

10k

100k

100

150

200

250

300

100

1000

CLPF (nF)

OUTPUT NOISE (mV p-p)

10% TO 90% RISE TIME (µs)

90% TO 10% FALL TIME (µs)

Figure 46. Output Noise, Rise and Fall Times vs. CLPF Capacitance, Single-

Carrier W-CDMA (TM1-64) at 2.14 GHz with PIN = 0 dBm

Figure 46 also shows how CLPF affects the response time of VOUT.

To measure this, a RF burst at 2.14 GHz at −10 dBm was applied to

the ADL5902. The 10% to 90% rise time and 90% to 10% fall

time is then measured. It is notable that the fall time is much

longer than the rise time. This can also be seen in the response

time plots, Figure 22, Figure 23, Figure 25, and Figure 26.

In applications where the response time is critical, a different

approach to signal filtering can be taken. This is shown in

Figure 47. The capacitor on the CLPF pin is set to the minimum

value that ensures that a valid rms computation is performed.

The job of noise removal is then handed off to an RC filter on

the VOUT pin. This approach ensures that there is enough

averaging to ensure good rms compliance and does not burden

the rms computation loop with extra filtering that significantly

slows down the response time. By finishing the filtering process

using an RC filter after VOUT, faster fall times can be achieved

with an equivalent amount of output noise. It must be noted

that the RC filter can also be implemented in the digital domain

after the analog-to-digital converter.

In Figure 47, CLPF is equal to 10 nF. This value was experimentally

determined to be the minimum capacitance that ensures good

rms compliance when the ADL5902 is driven by a 1 C W-CDMA

signal (TM1-64). This test was carried out by starting out with a

large capacitance value on the CLPF pin (for example, 10 μF).

The value of VOUT was noted for a fixed input power level (for

example, −10 dBm). The value of CLPF was then progressively

reduced (this can be done with press-down capacitors) until

the value of VOUT started to deviate from the original value (this

indicates that the accuracy of the rms computation is degrading

and that CLPF is getting too small).

BIAS AND POWER-

DOWN CONTROL

LINEAR-IN-dB VGA

(NEGATIVE SLOPE)

IDET

26pF

ADL5902

VREF

2.3V

TEMPERATURE

SENSOR

INLO

INHI

VPOS

POS

TEMP

VSET

VOUT

CLPF

COMM

VTGT

VREF

TADJ/PWDN

G = 5

ITGT

10nF

(SEE TABLE 6 AND

FIGURE 46.)

CFILTER

(SEE FIGURE 48.)

RFILTER

2kΩ

VOUT

Figure 47. Optimizing Setting Time and Residual Ripple

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