LT5506
40MHz to 500MHz
Quadrature Demodulator
with VGA
U
FEATURES
DESCRIPTIO
TheLT®5506isa40MHzto500MHzmonolithicintegrated
quadraturedemodulatorwithvariablegainamplifier(VGA),
designed for low voltage operation. It supports standards
that use a linear modulation format. The chip consists of
a VGA, quadrature down-converting mixers and lowpass
noise filters. The LO port consists of a divide-by-two stage
and LO buffers. The IC provides all building blocks for IF
down-conversionto IandQbasebandsignalswithasingle
supplyvoltageof1.8Vto5.25V. TheVGAgainhasalinear-
in-dB relationship to the control input voltage. Hard-clip-
ping amplifiers at the mixer outputs reduce the recovery
time from a signal overload condition. The lowpass filters
reduce the out-of-band noise and spurious frequency
components. The cut-off frequency of the noise filters is
approximately 8.8MHz. The external 2xLO frequency is
required to be twice the IF input frequency for the mixers.
The standby mode provides reduced supply current and
fast transient response into the normal operating mode
when the I/Q outputs are AC-coupled to a baseband chip.
, LTC and LT are registered trademarks of Linear Technology Corporation.
■
Wide Range 1.8V to 5.25V Supply
■
Frequency Range: 40MHz to 500MHz
■
–4dB to 59dB Variable Power Gain
■
THD < 0.12% (–58dBc)
at 800mVP-P Differential Output Level
■
8.8MHz I/Q Lowpass Output Noise Filters
■
IF Overload Detector
■
Baseband I/Q Amplitude Imbalance: 0.2dB
■
Baseband I/Q Phase Imbalance: 0.6°
■
6.8dB Noise Figure at Max Gain
■
Input IP3 at Low Gain: –0.5dBm
■
Low Supply Current: 27mA
■
Low Delay Shift Over Gain Control Range: 2ps/dB
■
Outputs Biased Up While in Standby
■
16-Lead QFN 4mUm x 4mm Package with Exposed Pad
APPLICATIO S
■
IEEE802.11
High Speed Wireless LAN
■
■
Wireless Local Loop
U
TYPICAL APPLICATIO
Total Harmonic Distortion vs
IF Input Level at 1.8V Supply
–30
1.8V
280MHz
IF INPUT
C2
C1
f
f
f
= 280MHz
= 280.1MHz
= 570MHz
IF, 1
IF, 2
2xLO
+
1µF
1nF
IF
L1
15nH
C3
10pF
L2
15nH
–35
–40
–45
–50
–55
–60
800mV DIFFERENTIAL OUT
P-P
V
CC
+
–
I
I
OUT
–
IF
OUT
IF DET
+
V
CTRL
C3
1.8pF
GAIN CONTROL
+
2xLO
Q
OUT
2xLO
C4
L3
39nH
560MHz
3.3pF
–
÷2
Q
OUT
INPUT
–
2xLO
–60
–40
–30
–20
–10
–50
LT5506
EN
ENABLE
STBY
STANDBY
GND
C5
3.3pF
IF INPUT POWER EACH TONE (dBm)
5506 TA01
5506 TA01b
5506fa
1