QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 792A
900MHZ HIGH LINEARITY, LOW POWER DOWNCONVERTING MIXER
LT5525
DESCRIPTION
Demonstration circuit 792A is a high linearity, low
power downconverting mixer featuring the LT5525.
The RF input frequency is 900MHz, and the IF output
frequency is 140MHz.
The LT5525 is a low power broadband mixer opti-
mized for high linearity applications such as point-to-
point data transmission, cable infrastructure and
wireless infrastructure systems. The device includes
an internally matched high speed LO amplifier driving
a double-balanced active mixer core. An integrated
RF buffer amplifier provides excellent LO-RF isolation.
The RF and IF ports can be easily matched across a
broad range of frequencies for use in a wide variety of
applications.
The LT5525 offers a high performance alternative to
passive mixers. Unlike passive mixers which have
conversion loss and require high LO drive levels, the
LT5525 delivers conversion gain at significantly lower
LO input levels and is much less sensitive to LO
power level variations.
Design files for this circuit board are available. Call
the LTC factory.
Table 1. Typical Performance Summary (V
CC
= 5V, EN = High, f
RF
= 1900MHz, P
RF
= -15dBm, f
LO
= 1760MHz, P
LO
= -5dBm, f
IF
=
140MHz, T
A
= 25°C, unless otherwise noted. Test circuit shown in Figure 2.)
PARAMETER
Supply Voltage
Supply Current
Maximum Shutdown Current
RF to LO isolation
Conversion Gain
Input 3 Order Intercept
Single Sideband Noise Figure
LO to RF Leakage
LO to IF Leakage
2RF-2LO Output Spurious Product
(f
RF
= f
LO
± f
IF
/2)
3RF-3LO Output Spurious Product
(f
RF
= f
LO
± f
IF
/3)
Input 1dB Compression
rd
CONDITION
EN = High
EN = Low
VALUE
3.6V to 5.3V
28mA
100µA
38dB
-1.9dB
2-Tone, -15dBm/tone,
∆f
= 1MHz
17.6dBm
15.1dB
-43dBm
-39dBm
f
RF
= 1830MHz, P
RF
= -15dBm, f
LO
= 1760MHz
f
RF
= 1806.67MHz, P
RF
= -15dBm, f
LO
= 1760MHz
-53dBc
-59dBc
+4dBm
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 792A
900MHZ HIGH LINEARITY, LOW POWER DOWNCONVERTING MIXER
APPLICATION NOTE
ABSOLUTE MAXIMUM INPUT RATING
Supply Voltage ..................................................... 5.5V
Enable Voltage.................................–0.3V to V
CC
+0.3V
RF Input Power .............................................. +10dBm
LO Input Power .............................................. +10dBm
FREQUENCY RANGE
Demonstration circuit 792A is optimized for evaluat-
ing the LT5525 for 1900MHz RF to 140MHz IF down-
conversion with either low-side or high- side LO in-
jection.
The RF input port is well matched with better than
12dB return loss over the frequency range from
1300MHz to 2300GHz. The IF output port is matched
for 140MHz with a 10dB return loss bandwidth of
50MHz.
With proper matching, the RF and IF ports can be
tuned for operation at other frequencies. Please refer
to the LT5525 datasheet Applications Information
section.
The LO input is internally matched to 50Ω.
TEST EQUIPMENT AND SETUP
Refer to
Error! Reference source not found.
for
proper measurement equipment setup.
Use high performance signal generators with low
harmonic output for 2-tone measurements. Other-
wise, low-pass filters at the signal generator outputs
should be used to suppress higher-order harmonics.
High quality combiners that provide broadband 50Ω
termination on all ports and have good port-to-port
isolation should be used. Attenuators on the outputs
of the signal generators are recommended to further
improve source isolation, to prevent the sources from
modulating each other and generating intermodula-
tion products.
Spectrum analyzers can produce significant internal dis-
tortion products if they are overdriven. Generally, spec-
trum analyzers are designed to operate at their best with
about –30dBm to -40dBm at their input. Sufficient
spectrum analyzer input attenuation should be used
to avoid saturating the instrument.
Before performing measurements on the DUT, the
system performance should be evaluated to ensure
that: 1) a clean input signal is obtained and 2) the
spectrum analyzer internal distortion is minimized.
QUICK START PROCEDURE
Demonstration circuit 792A is easy to set up to evalu-
ate the performance of the LT5525. Refer to
Error!
Reference source not found.
for proper measure-
ment equipment setup and follow the procedure be-
low:
1.
3.
4.
Connect DC power supply negative (-) output to
demo board GND pin (E2 or E4).
Connect DC power supply positive (+) output (3.6V
to 5.25V) to demo board Vcc pin (E1).
NOTE:
Do
Connect signal generator outputs to demo board
RFin port (SMA connector J1) and LOin port (SMA
connector J3) via coaxial cable.
Connect demo board IFout port (SMA connector
J2) to spectrum analyzer input via coaxial cable.
not exceed 5.5V, the absolute maximum
supply voltage.
5.
2.
Using a jumper cable, connect demo board Vcc pin
(E3) to EN pin (E1). Now the detector is enabled
(on) and is ready for measurement.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 792A
900MHZ HIGH LINEARITY, LOW POWER DOWNCONVERTING MIXER
the input power (in this case, -15dBm). All units
are in dBm.
11.
NOTE:
Make
sure that the power is not applied to the
EN pin before it is applied to the Vcc pin. The volt-
age on the EN pin must never exceed the voltage
on the Vcc pin +0.3V.
6.
Apply RF and LO input signals to perform AC
measurements.
not exceed +10dBm, the absolute maxi-
mum RF and LO input power.
NOTE:
Do
7.
Set the LO signal generator (#1) to provide a
1760MHz, -5dBm, CW signal to the demo board
LO input port.
Set the RF signal generators (#2 and #3) to provide
two –15dBm CW signals to the demo board RF in-
put port—one at 1900MHz, and the other at
1901MHz.
Set the Spectrum Analyzer’s frequency range to
capture the 140MHz IF output. Sufficient spectrum
analyzer input attenuation should be used to avoid
saturating the instrument.
gain and Input 3
rd
order intercept can
be measured:
Gc = P1 – Pin
IIP3 = (P1 – P3) / 2 + Pin
To measure the 2RF-2LO output spurious product,
turn off signal generator 3. Set signal generator 2
to f
RF
= f
LO
± f
IF
/2. In this case, f
RF
= 1760MHz +
140MHz / 2 = 1830MHz. Then the desired output
would be at 70MHz, and the 2RF-2LO output spur
would be at 140MHz. The dBc difference between
the two tones is the 2RF-2LO output spurious
product.
the same procedure for 3RF-3LO output
spurious product measurement. This time, set
signal generator 2 to f
RF
= f
LO
± f
IF
/3 = 1760MHz +
140MHz / 3 = 1806.67MHz. The desired output
would be at 46.67MHz, and the 3RF-3LO output
spur would be at 140MHz. The dBc difference be-
tween the two tones is the 3RF-3LO output spuri-
ous product.
12.
Follow
8.
9.
13.
Measure
RF to LO isolation, LO leakages, and Input
1dB compression.
10.
Conversion
a.
b.
14.
Single-Sideband
Where P1 is the power level of the fundamental
output tone at 140MHz or at 141MHz, P3 is the 3
rd
order product at 139MHz or at 142MHz, and Pin is
Noise Figure can be measured on a
noise figure meter. Refer to noise figure meter man-
ual for instructions. Be sure to use a high quality sig-
nal generator and a band-pass filter on the LO input.
A band-pass filter on the RF input port is required for
image suppression.
Figure 1.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 792A
900MHZ HIGH LINEARITY, LOW POWER DOWNCONVERTING MIXER
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 792A
900MHZ HIGH LINEARITY, LOW POWER DOWNCONVERTING MIXER
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