QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 696
IF RECEIVER, WIDE BB
LT5546
DESCRIPTION
Demonstration circuit 696 with LT5546 IC is a 40MHz
to 500MHz monolithic integrated quadrature demodu-
lator with variable gain amplifier (VGA), designed for
low voltage operation. It supports standards that use
linear modulation format. The chip consists of a
VGA, quadrature down-converting mixers and 17MHz
lowpass noise filters. The LO port consists of a di-
vide-by-two stage and LO buffers. The IC provides all
building blocks for IF down-conversion to I and Q
baseband signals with a single supply voltage of 1.8V
to 5.25V. The VGA gain has a linear-in-dB relation-
ship to the control input voltage. Hard-clipping am-
plifiers at the mixer outputs reduce the recovery time
from a signal overload condition. The lowpass filters
Table 1. Dip-Switch Setting For Different Operating Modes
EN
Low
Low
High
STBY
Low
High
Low or High
COMMENTS
Shutdown Mode
Standby Mode
Normal Operation Mode
reduce the out-of-band noise and spurious frequency
components. The –3dB corner frequency of the noise
filters is approximately 17MHz. The external 2XLO
frequency is required to be twice the IF input fre-
quency 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.
Design files for this circuit board are available. Call
the LTC factory.
LT is a trademark of Linear Technology Corporation
DC POWER CONSUMPTION MEASUREMENTS
1) Connect test equipment and power supplies to the
demo board as shown in Figure 1.
2) Set Power Supply #1 and Power Supply #2 to
+3.0V.
NOTE: One Power Supply can be used as well.
3) Set Power Supply #3 Between +4.75V and
+5.25V. This is the voltage source for the two Op-
Amps U2 and U3.
4) Set Power Supply #4 to 0V (minimum gain).
5) Shutdown Mode
a) Set dipswitches for EN and STBY to “On”
(Logic Low).
b) Measure Current in Vcc1. It should be ap-
proximately 0.2µA.
6) Standby Mode
a) Set EN dipswitch to “On” position (Logic
Low).
b) Set STBY dipswitch to “Off” position (Logic
High).
c) Measure Current in Vcc1. It should be ap-
proximately 3.6mA.
7) Normal Operation Mode
a) Set EN dipswitch to “Off” position (Logic
High).
b) Set STBY dipswitch to either “On” or “Off”.
c) Measure Current in Vcc1. It should be ap-
proximately 27mA.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 696
IF RECEIVER, WIDE BB
Figure 1. Test and Measurement Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 696
IF RECEIVER, WIDE BB
TOTAL HARMONIC DISTORTION MEASUREMENTS
1) Use setting steps 1 to 4 from previous DC power
consumption measurements.
2) Set dipswitch of EN and STBY to “Off “ position
(Logic High). The IC is in Normal Operation
Mode.
3) Set Signal Generator # 1 for f
IF
=280.0MHz, CW
mode, with P
IF
= –40dBm.
4) Set Signal Generator # 2 for f
IF
=280.1MHz, CW
mode, with P
IF
= –40dBm.
5) Set Signal Generator # 3 for f
LO
=570MHz, CW
mode, with P
LO
= -3dBm.
6) Set the Spectrum Analyzer to the following:
a) Center Frequency = 4.9MHz.
b) Frequency Span = 1MHz.
c) Amplitude Reference Level = 0dBm.
d) Res. BW = 10kHz,
e) Vid. BW = 30kHz.
Two CW tones will be on the screen of the spec-
trum analyzer, at 4.9MHz and 5.0MHz.
7) Slowly adjust the power supply #4 for V
ctrl
(V
ctrl
or
Gain Control Voltage) to set the output of Funda-
mental tones at –10dBm each.
NOTE: Do not adjust this voltage to more than
Vcc1. If necessary, adjust the P
IF
of either Signal
Generator #1 or Signal Generator #2 so that the
two tones are equivalent in level or Power value
(power delta of 0.3dB or less, preferably).
8) Record the actual value of the two tones on the
Spectrum Analyzer. These are the two Funda-
mental tones.
9) Set the Spectrum Analyzer to the following:
a) Center Frequency = 4.8MHz.
b) Frequency Span = 50kHz.
c) Amplitude Reference Level = –30dBm.
d) Averaging = ON.
e) Measure the lower IM3 Product on the Spec-
trum Analyzer at 4.8MHz.
10) Repeat step 9 for the Upper IM3 product at
5.1MHz.
NOTE: IM5 and IM7 products can be measured with
higher IF input signal levels.
BASEBAND LOWPASS FILTER, IF DETECT (OVERLOAD) AND PHASE &
AMPLITUDE MISMATCH MEASUREMENTS
1) Use setting steps 1 to 4 from previous DC power
consumption measurements.
2) Set signal generator # 3 for f
LO
=570MHz, CW
mode, with P
LO
= –3dBm.
3) Set Signal Generator # 1 for f
IF
=286.0MHz, CW
mode, with P
IF
= –30dBm.
4) Turn “Off” the RF output for the signal generator
#2.
5) Set dipswitch of EN and STBY to “Off “ position
(Logic High).
6) Set the Spectrum Analyzer to the following:
a) Start Frequency = 100kHz.
b) Stop Frequency = 50MHz.
c) Amplitude Reference Level = 0dBm.
d) Res. BW = 100kHz.
7) Slowly adjust the Power Supply #4 for Vcc4 (V
ctrl
or Gain Control Voltage) to set the output tone at
–4dBm.
8) BaseBand Filters frequency response can be
measured by sweeping input IF frequency from
286MHz to 335MHz. Correspondingly, BB output
will have 1 to 50MHz sweep. In case of manual
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 696
IF RECEIVER, WIDE BB
frequency sweep of IF input, the Spectrum Ana-
lyzer should be in “Maximum Hold” mode. One
marker should be placed at 1MHz point as a ref-
erence and another marker should be placed at
the point where the frequency response of the BB
filter has a 3.0dB drop. This represents the 3.0dB
corner frequency of the BB filter.
9) IF Detector (Overload) measurement:
a) Change Signal Generator # 1 Output power
with 1 or 2dB step size, from –30 to +8dBm.
b) IF Detector (Overload) Output voltage should
be in a range of 0.3 to 1.2 Volts correspond-
ingly.
10) BaseBand Phase and Amplitude mismatch meas-
urements.
a) Connect two (vertical) inputs of the oscillo-
scope to BB outputs.
NOTE: An Oscilloscope of 1GHz or faster is
recommended. Calibration and identical con-
necting cables are required. Measurements
should be done with internal or external 50-
ohm termination resistors.
b) Measure Phase and Amplitude error.
Phase error should be
±3.0
degrees maxi-
mum. Amplitude error should be within
±0.5dB.
NOTE: If available, an Impedance Analyzer like
the HP 4192A is recommended for BB Phase
and Amplitude mismatch measurements.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 696
IF RECEIVER, WIDE BB
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