LT5528 LINER [Linear Technology], LT5528 Datasheet - Page 8

• Manufacturer Part Number: LT5528
• Description: 1.5GHz to 2.4GHz High Linearity Direct Quadrature Modulator
• Manufacturer: LINER [Linear Technology]

BLOCK DIAGRA
APPLICATIO S I FOR ATIO
LT5528
The LT5528 consists of I and Q input differential voltage-
to-current converters, I and Q up-conversion mixers, an
RF output balun, an LO quadrature phase generator and
LO buffers.
V
8
CC
BBMI
BBPI
= 5V
RF
Figure 1. Simplifi ed Circuit Schematic of the LT5528
(Only I-Half is Drawn)
12pF
20Ω
R1A
U
C
R1B
23Ω
U
W
BALUN
R3
V
REF
LOMI
GND
CM
= 0.52V
BBMQ
BBPQ
BBMI
BBPI
W
14
16
7
5
2
R4
23Ω
R2B
V-I
V-I
4
GND
U
LOPI
6
20Ω
R2A
12pF
LT5528
FROM
9
90°
0°
Q
5528 F01
8
V
LO
3
CC
13
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 90Ω. At each of the
four baseband inputs, a fi rst-order low-pass fi lter using 20Ω
10
BALUN
12
GND
15
17
LT5528
5528 BD
11
1
RF
EN
5528f