Final Electrical Specifications
LT5502
400MHz Quadrature
IF Demodulator with RSSI
January 2001
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DESCRIPTIO
FEATURES
TheLT®5502isa70MHzto400MHzmonolithicintegrated
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
IFlimiterhas84dBsmall-signalgain, andabuilt-inreceive
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
■
Single 1.8V to 5.25V Supply
■
IF Frequency Range: 70MHz to 400MHz
■
84dB Limiting IF Gain
■
90dB Linear RSSI Range
■
7.7MHz Lowpass Output Filter
■
Baseband I/Q Amplitude Imbalance: <0.7dB
■
4dB Noise Figure
Low Supply Current: 25mA
Outputs Biased Up While in Standby
Shutdown Current: 1µA
24-Lead Narrow SSOP Package
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APPLICATIO S
■
IEEE802.11
■
High Speed Wireless LAN
■
Wireless Local Loop
AC-coupled to a baseband chip.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
I/Q Output Swing, RSSI Output vs IF Input Power
2V
C2
C1
1200
1000
800
1.2
1.0
0.8
0.6
0.4
0.2
1µF
1nF
C3
22nF
+
IF
V
CC
+
I
OUT
IF
INPUT
R1
240Ω
–
–
IF
BASEBAND
DIFFERENTIAL
I/Q OUTPUTS
I
OUT
90°
0°
+
2XLO
+
Q
OUT
600
2XLO
INPUT
÷2
–
Q
OUT
–
2XLO
EN
400
RSSI
LT5502
GND
ENABLE
C4
1.8pF
200
–85
–55
–40
–25
–10
5
–70
5502 TA01a
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-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
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