LT5502
1
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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IEEE802.11
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High Speed Wireless LAN
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Wireless Local Loop
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Single 1.8V to 5.25V Supply
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IF Frequency Range: 70MHz to 400MHz
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84dB Limiting IF Gain
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90dB Linear RSSI Range
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7.7MHz Lowpass Output Filter
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Baseband I/Q Amplitude Imbalance: <0.7dB
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4dB Noise Figure
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Low Supply Current: 25mA
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Outputs Biased Up While in Standby
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Shutdown Current: 1µA
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24-Lead Narrow SSOP Package
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
TYPICAL APPLICATIO
U
400MHz Quadrature
IF Demodulator with RSSI
, LTC and LT are registered trademarks of Linear Technology Corporation.
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.
I/Q Output Swing, RSSI Output vs IF Input Power
IF INPUT POWER (dBm)
–85
DIFFERENTIAL OUTPUT SWING (mV
P-P
)
1200
1000
800
600
400
200
RSSI OUTPUT (V)
1.2
1.0
0.8
0.6
0.4
0.2
–70
–55 –40 –25
5502 TA01b
–10 5
2XLO
+
2XLO
–
IF
+
IF
–
EN
V
CC
I
OUT
+
I
OUT
–
Q
OUT
+
Q
OUT
–
90°
0°
GND
2V
C2
1µF
C1
1nF
C4
1.8pF
RSSI
ENABLE
2XLO
INPUT
IF
INPUT
R1
240Ω
C3
22nF
BASEBAND
DIFFERENTIAL
I/Q OUTPUTS
5502 TA01a
÷2
LT5502
