lt5572 Linear Technology Corporation, lt5572 Datasheet - Page 14

• Manufacturer Part Number: lt5572
• Description: 1.5ghz To 2.5ghz High Linearity Direct Quadrature Modulator
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT5572
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.
14
Figure 15. LO Feedthrough and Image Rejection
vs Temperature After Calibration at 25°C
–40
–50
–60
–70
–80
–90
–40
LO FEEDTHROUGH
–20
U
TEMPERATURE (°C)
0
U
20
REJECTION
CALIBRATED WITH
P
IMAGE
RF
V
f
f
f
f
EN = HIGH
P
40
BBI
BBQ
LO
RF
= –10dBm
CC
LO
= f
= 2GHz
= 2MHz, 0°
= 5V
= 0dB
= 2MHz, 90°
W
BB
60
+ f
LO
5572 F15
80
U
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.
Figure 16. RF Output Power, Image Rejection and
LO Feedthrough vs Baseband Drive Voltage After
Calibration at 25°C
–10
–20
–30
–40
–60
–50
–70
–80
10
0
0
I AND Q BASEBAND VOLTAGE (V
P
RF
1
V
f
f
EN = HIGH
BBI
BBQ
CC
= 2MHz, 0°
2
= 5V
= 2MHz, 90°
LO FT
IR
3
f
f
EN = HIGH
P
LO
RF
LO
P-P(DIFF)
= f
= 2GHz
= 0dB
4
BB
25°C
85°C
–40°C
5572 F16
+ f
)
LO
5
5572f