ADRF6510(RevB) データシートの表示（PDF） - Analog Devices
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ADRF6510 Datasheet PDF : 32 Pages
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Data Sheet
EVM
The basic setup to test EVM for the ADRF6510 consisted of an
Agilent E4438C used as a RF signal source with an Agilent
InfiniiVision DSO7104B oscilloscope in conjunction with the
Agilent 89600 VSA software to sample the signal and compute
the EVM. The E4438C RF output drove the RF port of the
ADL5380 IQ demodulater, which in turn drove the baseband
differential inputs of the ADRF6510.
The I and Q outputs of the ADRF6510 were taken differentially
into two AD8130 difference amplifiers to convert them into
single-ended signals. The single-ended signals were connected
to the input channels of the oscilloscope, which captured the
modulated waveforms.
An overall baseband EVM performance was measured on the
ADRF6510. A modulation setting of 4 QAM and, unless
otherwise noted, a 5 MHz symbol rate were used, with a pulse
shaping filter alpha of 0.35. The analog gain of the ADRF6510
was adjusted to maintain 1.5 V p-p into a 1 kΩ differential load
impedance. Figure 50 shows EVM vs. input power for three
different IF frequencies. The input power is the integrated input
power over the bandwidth of the modulated signal.
In Figure 50, the ADRF6510 shows excellent EVM of better
than −-35 dB over a 50 dB range at a 0Hz IF. The user can
chose to use a complex IF of 5 MHz to achieve even a better
EVM of at least −40 dB over a 50 dB range.
0
–5
–10
–15
–20
–25
–30
–35
2.5MHz IF
–40
0Hz IF
–45
5MHz IF
–50
–80 –70 –60 –50 –40 –30 –20 –10 0 10
PIN (dBm)
Figure 50. EVM vs. RF Input Power Level; OFDS Pulled Low, COFS = 1 µF
EFFECT OF FILTER BANDWIDTH ON EVM
Care should be taken when selecting the filter bandwidth. In
a digital transceiver, the modulated signal is filtered by a pulse
shaping filter (such as a root-raised cosine filter) at both the
transmit and receive ends to guard against intersymbol inter-
ference (ISI). If additional filtering of the modulated signal is
done, the signal must be within the pass band of the filter. When
the corner frequency of the ADRF6510 filter begins to encroach
on the modulated signal, ISI is introduced and degrades EVM,
which can lead to loss of signal lock.
ADRF6510
While low-pass filtering with the ADRF6510 to reject out-of-
band undesired signals (blockers), more rejection of the
undesired signals may be required. If the filter bandwidth is set
to approximately the same as the signal bandwidth, the user
may trade some degradation of EVM for a gain in rejection of
the out-of-band undesired signals, by lowering the low-pass
filter bandwidth corner (for example, by 1 MHz).
Lowering the filter bandwidth to gain more rejection works
progressively better the lower the signal and filter bandwidths
are set to (see Figure 43). A 1 MHz change from 3 MHz filter
bandwidth to 2 MHz filter bandwidth yields about 20 dB more
rejection. Compare that to a 1 MHz change from 29 MHz filter
band-width to 28 MHz filter bandwidth, which will yield about
1 dB more in rejection.
Figure 51 shows that degradation of EVM as signal bandwidth
(positive frequency only) is swept while keeping the filter
bandwidth set to 5 MHz. Three different COFS capacitor values
were used.
0
FILTER BW CORNER
–5
–10
COFS = 1nF
–15
–20
–25
COFS = 100nF
–30
–35
–40
0
COFS = 1µF
2
4
6
8
10
12
14
SIGNAL BANDWIDTH (MHz)
Figure 51. EVM vs. Signal Bandwidth over COFS Values While Maintaining a
Filter Bandwidth of 5 MHz
EFFECT OF OUTPUT VOLTAGE LEVELS ON EVM
Output voltage level can affect EVM greatly when the signal
is compressed. When changing the output voltage levels of
the ADRF6510, take care that the output signal is not in compression, which
causes EVM degradation.
Rev. B | Page 21 of 32
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