QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1131A
HIGH SIGNAL LEVEL DOWNCONVERTING MIXER
1
LT5557
DESCRIPTION
Demonstration circuit 1131A is optimized for evalua-
tion of the LT5557 active downconverting mixer with
transformer-based IF output matching. Its RF input
and LO input ports are internally matched to 50Ω
ΩΩ
Ω,
from 1.6 to 2.3GHz, and from 1 to 5GHz, respectively.
The IF output is 50Ω
ΩΩ
Ω matched to 240MHz using an L-C
bandpass network followed by an 8:1 transformer.
The LT5557 active mixer is optimized for high linearity,
wide dynamic range downconverter applications. The
IC includes a high-speed differential LO buffer amplifier
driving a double-balanced mixer. Broadband, inte-
grated transformers on the RF and LO inputs provide
single-ended 50Ω
ΩΩ
Ω interfaces. The differential IF output
allows convenient interfacing to differential IF filters
and amplifiers, or is easily matched to drive a single-
ended 50Ω
ΩΩ
Ω load, with or without an external trans-
former.
The LT5557’s high level of integration minimizes the
total solution cost, board space and system-level varia-
tion.
Design files for this circuit board are available. Call
the LTC factory.
, LT, LTC, and LM are registered trademarks of Linear Technology Corporation.
Table 1.
Typical Demonstration Circuit Performance Summary (V
CC
= 3.3V, EN = High, TA = 25°C, f
RF
= 1950MHz, P
RF
= -6dBm, f
LO
=
1710MHz, P
LO
= -3dBm, IF output measured at 240MHz, unless otherwise noted. Test circuit shown in Figure 2.)
PARAMETER CONDITION VALUE
Supply Voltage 2.9 to 3.9V
Total Supply Current EN = High (> 2.7V) 81.6mA
Maximum Shutdown Current EN = Low (< 0.3V) 100µA
RF Input Frequency Range Return Loss > 12dB 1600 to 2300MHz
LO Input Frequency Range Return Loss > 10dB 1000 to 4200MHz
IF Output Frequency Range Return Loss > 10dB 220 to 260MHz
LO Input Power -8 to 2dBm
Conversion Gain 2.9dB
Input 3
rd
Order Intercept 2 RF tones, -6dBm/tone, ∆f = 1MHz 24.7dBm
Single-Sideband Noise Figure 11.7dB
LO to RF Leakage < -45dBm
LO to IF Leakage < -42dBm
RF to LO isolation > 42dB
RF to IF isolation > 41dB
2RF-2LO Output Spurious Product
(f
RF
= f
LO
± f
IF
/2) F
RF
= 1830MHz, P
RF
= -6dBm, f
IF
= 240MHz -53dBc
3RF-3LO Output Spurious Product
(f
RF
= f
LO
± f
IF
/3) F
RF
= 1790MHz, P
RF
= -6dBm, f
IF
= 240MHz -70dBc
Input 1dB Compression 8.8dBm
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1131A
HIGH SIGNAL LEVEL DOWNCONVERTING MIXER
2
APPLICATION NOTE
ABSOLUTE MAXIMUM INPUT RATING
Supply Voltage (V
CC1
, V
CC2
, IF
+
, IF
-
) ................. 4V
Enable Voltage ........................–0.3V to V
CC
+ 0.3V
LO Input Power........................................ +10dBm
LO Input DC Voltage ..................... -1V to V
CC
+ 1V
RF Input Power ........................................ +12dBm
RF Input DC Voltage..................................... ±0.1V
CAUTION: This part is sensitive to electrostatic dis-
charge (ESD). Observe proper ESD precautions when
handling the LT5557.
FREQUENCY RANGE
Demonstration circuit 1131A is optimized for evaluat-
ing the LT5557 IC for downconverting a RF signal in
the frequency range of 1.6GHz to 2.3GHz to a 240MHz
IF frequency with either low-side or high- side LO in-
jection.
The LT5557’s RF input is internally matched to 50Ω
ΩΩ
Ω
from 1.6GHz to 2.3GHz with better than 12dB return
loss. Its LO input port is internally matched to 50Ω
ΩΩ
Ω
from 1GHz to 5GHz with better than 10dB return loss.
The frequency range of both ports is easily extended
with simple external matching. Please refer to the
LT5557 datasheet Applications Information section.
Demonstration circuit 1131A utilizes a transformer for
impedance transformation and differential to single-
ended conversion on the IF output port. The IF output
is 50Ω
ΩΩ
Ω matched for 240MHz, but can be modified for
other IF frequencies. Equations for calculating com-
ponent values, as well as values for several common IF
frequencies are given in the LT5557 datasheet Applica-
tions Information section.
TEST EQUIPMENT AND SETUP
Refer to Figure 1 for proper measurement equipment
setup.
Use high performance signal generators with low har-
monic output for 2-tone measurements. Otherwise,
low-pass filters at the signal generator outputs should
be used to suppress higher-order harmonics.
High quality combiners that provide broadband 50Ω
ΩΩ
Ω
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 intermodulation
products.
Spectrum analyzers can produce significant internal
distortion products if they are overdriven. Generally,
spectrum analyzers are designed to operate at their
best with about –30dBm to -40dBm at their input. Suf-
ficient spectrum analyzer input attenuation should be
used to avoid saturating the instrument.
Before performing measurements on the DUT, the sys-
tem 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 1131A is easy to set up to evalu-
ate the performance of the LT5557. Refer to Figure 1
for proper measurement equipment setup and follow
the procedure below:
Note 1: Care should be taken to never exceed absolute
maximum input ratings.
Note 2: DC power should never be applied to the EN
pin before it is applied to the V
CC
pin.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1131A
HIGH SIGNAL LEVEL DOWNCONVERTING MIXER
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1.
Connect all test equipment as shown in Figure 1.
2.
Apply 3.3V DC supply power, and verify that the cur-
rent consumption is approximately 81.6mA.
3.
Apply RF and LO input signals to perform AC meas-
urements.
4.
Set the LO signal generator (#1) to provide a
1710MHz, -3dBm, CW signal to the demo board LO
IN port.
5.
Set the RF signal generators (#2 and #3) to provide
two –6dBm CW signals to the demo board RF IN
port—one at 1950MHz, and the other at 1951MHz.
6.
Set the Spectrum Analyzer’s frequency range to cap-
ture the 240MHz IF output. Sufficient spectrum ana-
lyzer input attenuation should be used to avoid satu-
rating the instrument.
7.
Conversion gain and Input 3
rd
order intercept can be
measured:
a.
Gc = P1 – Pin
b.
IIP3 = (P1 – P3) / 2 + Pin
Where P1 is the lowest power level of the two fun-
damental output tones at either 240MHz or at
241MHz, P3 is the largest 3
rd
order product at either
239MHz or at 242MHz, and Pin is the input power
(in this case, -6dBm). All units are in dBm.
8.
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
= 1710MHz +
240MHz / 2 = 1830MHz. Then the desired output
would be at 120MHz, and the 2RF-2LO output spur
would be at 240MHz. The dBc difference between
the two outputs is the 2RF-2LO output spurious
product.
9.
Follow the same procedure for 3RF-3LO output spu-
rious product measurement. This time, set signal
generator 2 to f
RF
= f
LO
+ f
IF
/3 = 1710MHz +
240MHz / 3 = 1790MHz. The desired output would
be at 80MHz, and the 3RF-3LO output spur would
be at 240MHz. The dBc difference between the two
outputs is the 3RF-3LO output spurious product.
10.
Measure RF to LO isolation, LO leakages, and Input
1dB compression.
11.
Single-Sideband Noise Figure can be measured on a
noise figure meter. Refer to noise figure meter
manual for instructions. Be sure to use a high qual-
ity signal generator and a band-pass filter on the LO
input. A band-pass filter on the RF input port is re-
quired for image suppression.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1131A
HIGH SIGNAL LEVEL DOWNCONVERTING MIXER
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Figure 1.
Proper Measurement Equipment Setup
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1131A
HIGH SIGNAL LEVEL DOWNCONVERTING MIXER
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