LT5503 Datasheet, PDF (1/20 Pages) Linear Technology – 1.2GHz to 2.7GHz Direct IQ Modulator and Mixer

FEATURES
s _{Single 1.8V to 5.25V Supply}
s _{Direct IQ Modulator with Integrated 90° Phase}
Shifter*
s _{Four Step RF Power Control}
s _{120MHz Modulation Bandwidth}
s _{Independent Double-Balanced Mixer}
s _{Modulation Accuracy Insensitive to Carrier Input}
Power
s _{Modulator I/Q Inputs Internally Biased}
U
APPLICATIO S
s _{IEEE 802.11 DSSS and FHSS}
s _{High Speed Wireless LAN (WLAN)}
s _{Wireless Local Loop (WLL)}
s _{PCS Wireless Data}
s _MMDS
, LTC and LT are registered trademarks of Linear Technology Corporation.
*Patent Pending
TYPICAL APPLICATIO
Final Electrical Specifications
LT5503
1.2GHz to 2.7GHz Direct
IQ Modulator and Mixer
DESCRIPTIO
October 2001
The LT^®5503 is a front-end transmitter IC designed for low
voltage operation, and is compatible with the LTC family of
WLAN products. The IC contains a high frequency quadra-
ture modulator with a variable gain amplifier (VGA) and a
balanced mixer. The modulator includes a precision 90°
phase shifter which allows direct modulation of an RF
signal by the baseband I and Q signals.
In a superheterodyne system, the mixer can be used to
generate the high-frequency RF input for the modulator by
mixing the system’s 1st and 2nd local oscillators.
The LT5503 modulator output delivers –3dBm at 2.5GHz.
The VGA allows output power reduction in three steps up
to 13dB with digital control. The baseband inputs are
internally biased for maximum input voltage swing at low
supply voltage. If needed, they can be driven with external
bias voltages.
V_CC2
2V
2.45GHz
BPF
V_CC1
2V
MIXER
ENABLE
MODULATOR
ENABLE
LO2IN
(750MHz)
V_CCLO2 V_CCLO1
MIXEN
MODEN
LO2
÷2
÷1
MX^– MX⁺
MODIN V_CCRF
BQ⁺ BQ^–
V_CCMOD
V_CCVGA
0°
90°
MODOUT
VGA
GND
DMODE LO1
LO1IN (2075MHz)
CONTROL
LOGIC
GC1 GC2
BI⁺ BI^–
2.45GHz
5503 F01 MODULATED
RFOUT
Figure 1. 2.45GHz Transmitter Application, Carrier for Modulator Generated by Upmixer
2.45GHz Modulated Output
Power vs Supply Voltage
–2
–3
–4
–5
–6
1.8
P_LO1 = –12dBm
P_LO2 = –18dBm
BASEBAND = 1V_P-P
T_A = 27°C
2.4 3.0 3.6 4.2 4.8 5.4
SUPPLY VOLTAGE (V)
5503 TA01b
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1