ADRF6510ACPZ-WP Analog Devices Inc, ADRF6510ACPZ-WP Datasheet - Page 20

• Manufacturer Part Number: ADRF6510ACPZ-WP
• Manufacturer: Analog Devices Inc

Specifications of ADRF6510ACPZ-WP

• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 32
• Lead Free Status / RoHS Status: Supplier Unconfirmed

ADRF6510
An overall RF-to-baseband EVM performance was obtained
with the
An 840 MHz RF signal with a modulation setting of 64 QAM
and a 7 MHz symbol rate was used. The local oscillator (LO) is
set at 1680 MHz to obtain 840 MHz at the quadrature core after
the divide-by-2 stage. The analog gain of the ADRF6510 was
adjusted to maintain 1.5 V p-p into a 1 kΩ load impedance.
Figure 49 shows EVM vs. input power and the corresponding
analog gain voltage.
LOW IF IMAGE REJECTION
The image rejection ratio is the ratio of the intermediate frequency
(IF) signal level produced by the desired input frequency to that
produced by the image frequency. The image rejection ratio is
expressed in decibels (dB). Appropriate image rejection is critical
because the image power can be much higher than that of the
desired signal, thereby plaguing the downconversion process.
Figure 51 illustrates the image problem. If the upper sideband is
the desired band, a 90° shift to the Q channel cancels the image
at the lower sideband. In the same way, if the lower sideband is
the desired band, a 90° shift to the I channel cancels the image
at the upper sideband. Phase and gain balance between the I
and Q channels are critical for high levels of image rejection.
32
30
28
26
24
22
20
–65
ADL5387
–55
Figure 49. EVM vs. RF Input Power Level
ω
IQ demodulator preceding the ADRF6510.
LSB
ω
RF INPUT POWER (dBm)
–45
IF
ω
LO
ω
IF
–35
ω
USB
–25
SINω
COSω
LO
LO
–15
t
t
Figure 51. Illustration of the Image Problem
–5
2.5
2.0
1.5
1.0
0.5
0
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–ω
–ω
IF
IF
Figure 50 shows the image rejection of the ADL5387 and the
ADRF6510 for various baseband frequencies. The modulation
is 64 QAM with a 7 MHz symbol rate. Note the following:
•
•
To the right of the 5 MHz center frequency, the filter is
programmed to be 5 MHz greater than the centered base-
band frequency. This ensures that the signal edge is well
within the pass band of the filter. In such cases, where the
filter bandwidth is set to be greater than the signal bandwidth,
the image rejection of the ADL5387 tends to be the limiting
factor, and the ADRF6510 has minimal effects.
To the left of 5 MHz—specifically at a center frequency
of 3.5 MHz—the filter corner is lowered to the baseband
signal edge, degrading the image rejection. When the
centered baseband frequency is 3.5 MHz and the filter is
set at 7 MHz (instead of a safer 8 MHz), the filter corner
conflicts with the edge of the modulated signal. Channel
mismatch in group delay characteristics and variation in
absolute group delay (from the normal flat response) tend
to degrade image rejection.
0
0
45
40
35
30
25
20
15
10
Figure 50. Image Rejection of the ADL5387 and ADRF6510
5
0
3
+ω
+ω
IF
IF
5
AT CENTER FREQUENCIES GREATER
THAN 5MHz, FILTER CORNER IS
SET TO 5MHz HIGHER THAN SIGNAL EDGE
AT CENTER FREQUENCY = 3.5MHz,
FILTER CORNER IS SET TO 7MHz
–90°
+90°
BASEBAND FREQUENCY (MHz)
0°
0°
7
9
0
0
11
+ω
+ω
IF
IF
13
1
5