LT5502 Datasheet, PDF (1/12 Pages) Linear Technology – 400MHz Quadrature IF Demodulator with RSSI

FEATURES
s _{Single 1.8V to 5.25V Supply}
s _{IF Frequency Range: 70MHz to 400MHz}
s _{84dB Limiting IF Gain}
s _{90dB Linear RSSI Range}
s _{7.7MHz Lowpass Output Filter}
s _{Baseband I/Q Amplitude Imbalance: <0.7dB}
s _{4dB Noise Figure}
s _{Low Supply Current: 25mA}
s _{Outputs Biased Up While in Standby}
s _{Shutdown Current: 1µA}
s _{24-Lead Narrow SSOP Package}
U
APPLICATIO S
s _IEEE802.11
s _{High Speed Wireless LAN}
s _{Wireless Local Loop}
TYPICAL APPLICATIO
Final Electrical Specifications
LT5502
400MHz Quadrature
IF Demodulator with RSSI
January 2001
DESCRIPTIO
The LT^®5502 is a 70MHz to 400MHz monolithic integrated
quadrature IF demodulator. It consists of an IF limiter,
quadrature down mixers, integrated lowpass filters, and
divide-by-two LO buffers. The demodulator provides all
building blocks for demodulation of I and Q baseband
signals with a single supply voltage of 1.8V to 5.25V. The
IF limiter has 84dB small-signal gain, and a built-in receive
signal strength indicator (RSSI) with over 90dB linear
range. The input referred noise-spectral-density is
1.45nV/√Hz, which is equivalent to a 4dB noise figure
when the input is terminated with a 50Ω source. The
integrated lowpass output filters act as antialiasing and
pulse-shaping filters for demodulated I/Q-baseband sig-
nals. The 3dB cutoff frequency of the filters is about
7.7MHz. The VCO frequency is required to be twice the
desired operating frequency to provide quadrature local
oscillator (LO) signals to the mixers. The standby mode
provides fast transient response to the receive mode with
reduced supply current when the I/Q outputs are
AC-coupled to a baseband chip.
, LTC and LT are registered trademarks of Linear Technology Corporation.
IF
INPUT
2XLO
INPUT
C2
1µF
C3
22nF
IF⁺
R1
240Ω
IF ^–
2XLO⁺
2XLO^–
ENABLE EN
2V
C1
1nF
V_CC
90°
÷2
0°
LT5502
GND
I/Q Output Swing, RSSI Output vs IF Input Power
1200
1.2
I_OUT+
I_OUT–
Q_OUT+
Q_OUT–
RSSI
BASEBAND
DIFFERENTIAL
I/Q OUTPUTS
C4
1.8pF
5502 TA01a
1000
1.0
800
0.8
600
0.6
400
0.4
200
–85
0.2
–70 –55 –40 –25 –10 5
IF INPUT POWER (dBm)
5502 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.
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