LT5558 Просмотр технического описания (PDF) - Linear Technology
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LT5558 Datasheet PDF : 16 Pages
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LT5558
APPLICATIONS INFORMATION
J1
BBIM
J2
BBIP
VCC
R1
100
VCC EN
J4
LO
IN
J5
BBQM
16 15 14 13
BBMI GND BBPI VCC
1
12
EN
GND
2
GND
11
RF
3
LO
LT5558
10
GND
4
GND
9
GND
17
GND
BBMQ GND BBPQ VCC
5678
C1
100nF
GND
C2
100nF
J3
RF
OUT
J6
BBQP
BOARD NUMBER: DC1017A
5558 F07
Figure 7. Evaluation Circuit Schematic
Figure 8. Component Side of Evaluation Board
Application Measurements
The LT5558 is recommended for base-station applications
using various modulation formats. Figure 10 shows a
typical application.
Figure 11 shows the ACPR performance for CDMA2000
using one and three channel modulation. Figures 12 and 13
illustrate the 1- and 3-channel CDMA2000 measurement.
To calculate ACPR, a correction is made for the spectrum
analyzer noise floor (Application Note 99).
12
Figure 9. Bottom Side of Evaluation Board
If the output power is high, the ACPR will be limited by the
linearity performance of the part. If the output power is
low, the ACPR will be limited by the noise performance of
the part. In the middle, an optimum ACPR is obtained.
Because of the LT5558’s very high dynamic-range, the test
equipment can limit the accuracy of the ACPR measure-
ment. Consult Design Note 375 or the factory for advice
on ACPR measurement if needed.
The ACPR performance is sensitive to the amplitude mis-
match of the BBIP and BBIM (or BBQP and BBQM) inputs.
This is because a difference in AC current 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.
LO feedthrough and image rejection performance may
be improved by means of a calibration procedure. LO
feedthrough is minimized by adjusting the differential DC
offset at the I and the Q baseband inputs. Image rejec-
tion can be improved by adjusting the gain and the phase
difference between the I and the Q baseband inputs. The
LO feedthrough and Image Rejection can also change
as a function of the baseband drive level, as depicted in
Figure 14.
5558fa
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