LT5568-2EUF-PBF LINER [Linear Technology], LT5568-2EUF-PBF Datasheet - Page 8

• Manufacturer Part Number: LT5568-2EUF-PBF
• Description: GSM/EDGE Optimized, High Linearity Direct Quadrature Modulator
• Manufacturer: LINER [Linear Technology]

BLOCK DIAGRA
APPLICATIO S I FOR ATIO
LT5568-2
V
The LT5568-2 consists of I and Q input differential volt-
age-to-current converters, I and Q up-conversion mixers,
an RF output balun, an LO quadrature phase generator
and LO buffers.
8
CC
BBMI
BBPI
= 5V
RF
Figure 1. Simplifi ed Circuit Schematic of the LT5568-2
(Only I-Half is Drawn)
12pF
25Ω
R1A
U
C
23Ω
R1B
U
W
BALUN
R3
V
BBMQ
BBPQ
BBMI
REF
BBPI
LOMI
GND
= 540mV
CM
W
14
16
7
5
2
V-I
V-I
R4
4
R2B
23Ω
GND
U
6
LOPI
12pF
R2A
25Ω
LT5568-2
9
90°
FROM
0°
55682 F01
Q
8
V
LO
3
CC
External I and Q baseband signals are applied to the dif-
ferential baseband input pins, BBPI, BBMI, and BBPQ,
BBMQ. These voltage signals are converted to currents and
translated to RF frequency by means of double-balanced
up-converting mixers. The mixer outputs are combined
in an RF output balun, which also transforms the output
impedance to 50Ω. The center frequency of the resulting
RF signal is equal to the LO signal frequency. The LO input
drives a phase shifter which splits the LO signal into in-
phase and quadrature LO signals. These LO signals are then
applied to on-chip buffers which drive the up-conversion
mixers. Both the LO input and RF output are single-ended,
50Ω-matched and AC coupled.
Baseband Interface
The baseband inputs (BBPI, BBMI), (BBPQ, BBMQ) present
a differential input impedance of about 100Ω. At each of the
four baseband inputs, a fi rst-order lowpass fi lter using 25Ω
13
10
BALUN
12
GND
15
LT5568-2
17
55682 BD
11
1
RF
EN
55682f