Datasheet

LTC6946
27
6946fa
APPLICATIONS INFORMATION
LTC6946-2 Driving a Modulator
MUTE GND RF
–
RF
+
V
RF
+
BB
REF
+
REF
–
V
REF
+
CP
V
CP
+
GND
V
REFO
+
REFO
STAT
CS
SCLK
SDI
SDO
V
D
+
V
VCO
+
GND
CM
A
CM
B
CM
C
GND
TB
TUNE
LTC6946-2
SPI BUS
3.3V
470pF
51.1Ω
+
15Ω
5V
R
Z
1μF
3.3V
LOOP COMPENSATION
COMPONENT VALUES ARE
APPLICATION SPECIFIC
DEPENDING ON THE LO
FREQUENCY RANGE AND
STEP SIZE AND THE PHASE
NOISE OF THE REFERENCE
C
I
0.01μF
0.1μF
3.3V
3.3V
1μF
0.01μF
0.01μF
2.2μF
C
P
0.01μF
470pF
10MHz
REFERENCE
3.3V3.3V
THE UNUSED RF
–
OUTPUT
IS AVAILABLE TO DRIVE
ANOTHER 50Ω LOAD
68nH
LOM
LO = 1950MHz
TOKO
4DFB-1950L-10
3.3V
V
CC2
RF
GNDRF
BBPI
BBMI
BBPQ
BBMQ
LOP
GND
LINOPT
6946 TA02
LTC5588-1
V
CC1
1nF
68nH
0.1μF
4.7μF
3.3V
1nF
50Ω
1Ω
1.3Ω
1nF
50Ω
10nF
1810MHz
140MHz
VGA
1nF
4.7μF
0°
90°
BASEBAND
GENERATOR
EN EN
I-DAC
Q-DAC
LTC2630
PA
RF FREQUENCY (MHz)
1802.5
–120
POWER IN 30kHz BW (dBm)
–90
–90
–80
–70
–60
–50
1807.5
1812.5
6946 TA02b
–40
–30
MEASURED SIGNAL
MEASUREMENT NOISE FLOOR
–110
1817.5
≈–80dBc
Measured W-CDMA ACPR
(3.84MHz Bandwidth)
LTC6946-2 Modulator Application
Phase Noise
OFFSET FREQUENCY (Hz)
–130
–140
PHASE NOISE (dBc/Hz)
–110
–90
–150
–120
–100
100 10k 100k 1M 10M
6946 TA02c
–160
1k
RMS NOISE = 0.281°
f
RF
= 1950MHz
f
PFD
= 2MHz
OD = 2
f
STEP
= 1MHz