LT5572
14
5572f
APPLICATIO S I FOR ATIO
WUU
U
Figure 15. LO Feedthrough and Image Rejection
vs Temperature After Calibration at 25°C
Figure 16. RF Output Power, Image Rejection and
LO Feedthrough vs Baseband Drive Voltage After
Calibration at 25°C
TEMPERATURE (°C)
–40
–90
LO FEEDTHROUGH (dBm), IR (dB)
–80
–70
–60
–50
–40
–20
02040
5572 F15
60 80
V
CC
= 5V
f
BBI
= 2MHz, 0°
f
BBQ
= 2MHz, 90°
f
LO
= 2GHz
f
RF
= f
BB
+ f
LO
EN = HIGH
P
LO
= 0dB
IMAGE
REJECTION
LO FEEDTHROUGH
CALIBRATED WITH
P
RF
= –10dBm
I AND Q BASEBAND VOLTAGE (V
P-P(DIFF)
)
0
–80
PRF, LOFT (dBm), IR (dBc)
–70
–50
–40
–30
2
4
5
10
P
RF
LO FT
IR
5572 F16
–60
13
–20
–10
0
25°C
85°C
–40°C
V
CC
= 5V
f
BBI
= 2MHz, 0°
f
BBQ
= 2MHz, 90°
EN = HIGH
f
LO
= 2GHz
f
RF
= f
BB
+ f
LO
EN = HIGH
P
LO
= 0dB
Because of the LT5572’s very high dynamic range,
the test equipment can limit the accuracy of the ACPR
measurement. Consult the factory for advice on the ACPR
measurement if needed.
The ACPR performance is sensitive to the amplitude match
of the BBIP and BBIM (or BBQP and BBQM) input voltage.
This is because a difference in AC voltage amplitude will
give rise to a difference in amplitude between the even-order
harmonic products generated in the internal V-I converter.
As a result, they will not cancel out entirely. Therefore, it
is important to keep the amplitudes at the BBIP and BBIM
(or BBQP and BBQM) inputs as equal as possible.
When the temperature is changed after calibration, the
LO feedthrough and the image rejection performance will
change. This is illustrated in Figure 15. The LO feedthrough
and image rejection can also change as a function of the
baseband drive level as depicted in Figure 16.
