ADL5511ACPZ-R7 datasheet(21/29 Pages) AD

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Data Sheet

ADL5511

Rev. C | Page 21 of 29

For applications that are not response time critical, a relatively

large capacitor can be placed on the FLT4. There is no maximum

capacitance limit for CFLT4.

Figure 50 shows how output noise, rise time and fall time vary

vs. CFLT4 when the ADL5511 is driven by an 1.9 GHz LTE carrier

with a bandwidth of 10 MHz (LTE Test Model E-TM1_1_10MHz,

peak-to-average ratio = 11.99 dB).

Figure 50. Output Noise, Rise and Fall Times vs. CFLT4 Capacitance, 10 MHz

BW LTE Carrier (LTE Test Model E-TM1_1_10MHz) at 1.9 GHz with PIN = 0 dBm

ENVELOPE TRACKING ACCURACY

The envelope tracking accuracy of the ADL5511 is measured in

terms of the higher order distortion of the envelope output when

the RF input signal is AM modulated using a low-harmonic

sinusoid at a given frequency. Such an input sinusoidal envelope

has been generated using the ADL5390 multiplier modulator.

This generates a double sideband AM modulated signal of a

known modulation index. In this measurement, the ADL5511

acts as free-running AM demodulator without requiring a local

oscillator to demodulate the signal.

Figure 51. THD on VENV vs. RF Input Level; 1900 MHz RF Input, AM Modulated

by a 20 MHz Sine Wave (Modulation Index = 0.25), VENV Output AC-Coupled

into a 50 Ω Spectrum Analyzer Load

Figure 51 shows such a plot total harmonic distortion (THD) of

the VENV output vs. RF input power for the modulation index

of 0.25.

As the input power level increases, the THD improves until it

sharply degrades at an input power level of approximately 13

dBm. This sharp decrease is caused by the clipping of the AM

signal’s peak envelope. Figure 51 also shows carrier leakage at

VENV in dBc with respect to the input carrier amplitude.

This measurement, when conducted over the full input power

range of the ADL5511, suffers from measurement inaccuracies

of the input modulated signal due to the spectrum analyzer’s

noise floor and therefore does not accurately reveal the ADL5511’s

limitations at the lower end of the measurement range. In

addition to this, the process of generating an AM signal for this

test (using the ADL5390 multiplier) is not perfect and resulted

in a source signal whose envelope was not harmonically pure.

TIME DOMAIN ENVELOPE TRACKING ACCURACY

The envelope tracking accuracy of the ADL5511 can also be

assessed in the time domain by looking at the input peak power

levels that cause clipping.

The usable rms input power range of the ADL5511 varies

depending on the desired accuracy level and the peak-to-average

ratio of the input signal. Figure 4 shows the linear operating range

of the VENV output when the RF input is driven by unmodulated

sine waves at various frequencies. This shows operation up to rms

input levels of approximately 19 dBm. If the signal has a peak-

to-average ratio that is greater than the square root of two, the

usable input range on RFIN will decrease. In general, the maximum

input power for linear operation should be determined by the

peak envelope power (PEP) of the input signal. Figure 52 shows

the time-domain response of the VENV output to a 900 MHz

LTE carrier with a bandwidth of 20 MHz (Test Model E-

TM1_2_20MHz). The signal level of the carrier (7 dBm rms,

19 dBm PEP) was deliberately increased until clipping was

observed at the VENV output.

Note that the peak envelope power of a signal is derived based on

the rms level of the signal during a peak cycle, that is V p-p/√2. For

example, a signal that achieves a peak voltage of 10 V (or 20 V p-p)

has a PEP of 30 dBm. According to this definition, the PEP of a

sine wave is equal to its rms power level because it has a constant

envelope.

0.1

100

1000

10000

100000

1000000

10000000

100

200

300

400

500

600

700

800

100

1000

CFLT4 (nF)

OUTPUT NOISE (mV p-p)

10% TO 90% RISE TIME (µs)

90% TO 10% FALL TIME (µs)

–80

–70

–60

–50

–40

–30

–20

–10

–35

–30

–25

–20

–15

–10

–5

RFIN (dBm)

THD (dBc)

CARRIER SUPPRESSION (dBc)

ENVELOPE GAIN (dB)

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