lt5558 Linear Technology Corporation, lt5558 Datasheet - Page 8

• Manufacturer Part Number: lt5558
• Description: 600mhz To 1100mhz High Linearity Direct Quadrature Modulator
• Manufacturer: Linear Technology Corporation

BLOCK DIAGRAM
LT5558
PIN FUNCTIONS
The LT5558 consists of I and Q input differential voltage-
to-current converters, I and Q up-conversion mixers, an
RF output signal combiner/balun, an LO quadrature phase
generator and LO buffers.
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 in-
put drives a phase shifter which splits the LO signal into
in-phase and quadrature LO signals. These LO signals
LO (Pin 3): LO Input. The LO input is an AC-coupled single-
ended input with approximately 50Ω input impedance at
RF frequencies. Externally applied DC voltage should be
within the range –0.5V to (V
turning on ESD protection diodes.
BBPQ, BBMQ (Pins 7, 5): Baseband Inputs for the
Q-channel. The differential input impedance is 3kΩ. These
pins are internally biased at about 2.1V. Applied common
mode voltage must stay below 2.5V.
V
nected to each other internally. It is recommended to use
APPLICATIONS INFORMATION
8
CC
(Pins 8, 13): Power Supply. Pins 8 and 13 are con-
CC
+ 0.5V) in order to avoid
BBMQ
BBPQ
BBMI
BBPI
14
16
7
5
2
4
V-I
V-I
GND
6
9
90°
0°
8
V
CC
13
LO
0.1μF capacitors for decoupling to ground on each of
these pins.
RF (Pin 11): RF Output. The RF output is an AC-coupled
single-ended output with approximately 50Ω output im-
pedance at RF frequencies. Externally applied DC voltage
should be within the range –0.5V to (V
to avoid turning on ESD protection diodes.
BBPI, BBMI (Pins 14, 16): Baseband Inputs for the
I-channel. The differential input impedance is 3kΩ. These
pins are internally biased at about 2.1V. Applied common
mode voltage must stay below 2.5V.
3
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) pres-
ent a differential input impedance of about 3kΩ. At each
of the four baseband inputs, a low-pass fi lter using 200Ω
and 1.8pF to ground is incorporated (see Figure 1), which
limits the baseband –1dB bandwidth to approximately
250MHz. The common-mode voltage is about 2.1V and
is slightly temperature dependent. At T
common-mode voltage is about 2.28V and at T
it is about 2.01V.
10
BALUN
12
GND
LT5558
15
17
11
1
5558 BD
RF
EN
CC
+ 0.5V) in order
A
= -40°C, the
A
= 85°C
5558fa