LT5571 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT5571' PDF : 16 Pages View PDF
LT5571
APPLICATIONS INFORMATION
Application Measurements
The ACPR performance is sensitive to the amplitude
The LT5571 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’s noise floor (Application Note 99).
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.
mismatch 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) 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
offsets at the I and the Q baseband inputs. Image rejection
can be improved by adjusting the amplitude and phase
difference between the I and the Q baseband inputs. The
Because of the LT5571’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
LO feedthrough and Image Rejection can also change
as a function of the baseband drive level, as depicted in
Figure 14.
on ACPR measurement if needed.
I-DAC
14
16 V-I
8, 13
VCC
LT5571
5V
100nF
×2 RF = 620MHz
TO 1100MvHz
–40
DOWNLINK TEST
MODEL 64 DPCH
–50
3-CH ACPR
–60
3-CH AltCPR
–110
–120
1-CH
ACPR –130
EN
Q-DAC
I-CH
1
0°
90°
7 Q-CH
5 V-I
11
PA
BALUN
–70
–80
1-CH AltCPR
3-CH NOISE
–140
1-CH NOISE
–150
BASEBAND
GENERATOR
2, 4, 6, 9, 10, 12, 15, 17
3
VCO/SYNTHESIZER
5571 F10
–90
–30 –25 –20 –15 –10 –5
–160
0
RF OUTPUT POWER PER CARRIER (dBm)
5571 F11
Figure 10. 620MHz to 1.1GHz Direct Conversion Transmitter Application
Figure 11. CDMA2000 ACPR, ALTCPR and Noise vs
RF Output Power at 900MHz for 1 and 3 Carriers
–30
DOWNLINK TEST
–40 MODEL 64 DPCH
–50
–60
–70
–80
–90
–100
UNCORRECTED
SPECTRUM
CORRECTED
SPECTRUM
–110
–120
–130
896.25
SPECTRUM ANALYSER NOISE FLOOR
897.75 899.25 900.75 902.25 903.75
RF FREQUENCY (MHz)
5571 F12
Figure 12. 1-Channel CDMA2000 Spectrum
–30
DOWNLINK
–40 TEST MODEL
64 DPCH
–50
–60
–70
UN-
CORRECTED
–80 SPECTRUM
–90
SPECTRUM
ANALYSER
NOISE
FLOOR
–100
–110
–120
–130
894
CORRECTED SPECTRUM
896 898 900 902 904 906
RF FREQUENCY (MHz)
5571 F13
Figure 13. 3-Channel CDMA2000 Spectrum
20
10
PRF
0
–10
–20
25°C
–30
85°C
–40°C
LO FT
–40
–50
IR
–60
–70
–80
–90
0
fBBI = 2MHz, 0°
VCC = 5V, fBBQ = 2MHz, 90°
EN = HIGH, fRF = fBB + fLO
fLO = 900MHz, PLO = 0dBm
1
2
3
4
5
I AND Q BASEBAND VOLTAGE (VP-P,DIFF)
5571 F14
Figure 14. Image Rejection and LO Feed-
Through vs Baseband Drive Voltage After
Calibration at 25°C
5571f
13
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