Linear Technology 642 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 642
HIGH LINEARITY UPCONVERTING MIXER
1
LT5521
DESCRIPTION
Demonstration circuit 642 is an upconverting mixer
featuring the LT
®
5521. The LT
®
5521 is a 10MHz to
3.7GHz High Linearity Up/Downconverting Mixer
optimized for wireless and cable infrastructure
applications. A high-speed, internally matched LO
amplifier drives a double-balanced mixer core,
allowing the use of a low power, single-ended LO
source.
The IF port can be easily matched to a broad range of
frequencies for use in many different applications.
Demonstration circuit 642 is designed for an RF
output frequency range from 1.75GHz to 2.15GHz and
is optimized for a 250MHz IF input frequency.
Design files for this circuit board are available. Call
the LTC factory.
LT is a registered trademark of Linear Technology Corporation.
Table 1. Typical Performance Summary (TA= 25°C)
PARAMETER CONDITION (f
IF
= 250MHz, f
LO
=1700MHz) VALUE
Supply Voltage 4.5V to 5.25V
Supply Current V
CC
= 5V, EN = High 82mA
Maximum Shutdown Current V
CC
= 5V, EN = Low 100µA
RF Frequency Range 1.75GHz to 2.15GHz
IF Input Return Loss Z
0
= 50, with external matching 15dB
LO Input Return Loss Z
0
= 5012dB
RF Output Return Loss Z
0
= 5012dB
LO Input Power -10dBm to 0dBm
Conversion Gain P
IF
= -7dBm, P
LO
= -5dBm -0.5dB
SSB Noise Figure
P
LO
= -5dBm
12.5dB
Input 3
rd
Order Intercept 2-Tone, -7dBm/Tone,
∆ f = 5MHz, P
LO
= -5dBm
+24.2dBm
Input 2
nd
Order Intercept 2-Tone, -7dBm/Tone,
∆ f = 5MHz, P
LO
= -5dBm
+49dBm
Input 1dB Compression P
LO
= -5dBm +10dBm
LO to RF leakage P
LO
= -5dBm -42dBm
LO to IF leakage P
LO
= -5dBm -40dBm

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 642
HIGH LINEARITY UPCONVERTING MIXER
2
APPLICATION NOTE
FREQUENCY RANGE
Demonstration circuit 642 is optimized for an IF input
frequency of 250MHz. This frequency is set by the
input IF matching components on the PCB. Other
values may be used to maintain best performance for
IF frequencies ranging from 10MHz to 3GHz.
CURRENT CONSUMPTION
If lower power consumption is required, the LT
®
5521’s
supply current can be reduced by increasing the value
of the DC return resistors, R1, R2. Operation at a
lower supply current will, however, degrade linearity.
LO TO RF LEAKAGE
Minimum LO to RF leakage is realized when R1 & R2
are closely matched; 0.1% tolerance resistors are
recommended for this reason. Resistors with a greater
tolerance (ie; 1%) may be used with some degradation
of LO to RF leakage.
QUICK START PROCEDURE
Demonstration circuit 642 is easy to set up to evaluate
the performance of the LT
®
5521. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
NOTE:
a. Use high performance signal generators with low
harmonic output for 2
nd
& 3
rd
order distortion
measurements. Otherwise, low-pass filters at
the signal generator outputs should be used to
suppress harmonics, particularly the 2
nd
harmonic.
b. High quality combiners that provide a 50 ohm
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
and to reduce reflection into the sources.
1. Connect all test equipment as shown in Figure 1.
2. Set the DC power supply’s current limit to 90mA,
and adjust output voltage to 5V.
3. Connect Vcc to the 5V DC supply, and then connect
EN to 5V; the mixer is enabled (on).
4. Set Signal Generator #1 to provide a 1700MHz,
-5dBm, CW signal to the demo board LO input port.
5. Set the Signal Generators #2 and #3 to provide two
-10dBm CW signals to the demo board RF input
port—one at 250MHz, and the other at 255MHz.
6. To measure 3
rd
order distortion and conversion gain,
set the Spectrum Analyzer start and stop
frequencies to 1940MHz and 1965MHz, respectively.
Sufficient spectrum analyzer input attenuation
should be used to avoid distortion in the instrument.
7. The 3
rd
order intercept point is equal to (P
1
– P
3
) / 2
+ P
in
, where P
1
is the power level of the two
fundamental output tones at 1950MHz and
1955MHz, P
3
is the 3
rd
order product at 1945MHz
and 1960MHz, and P
in
is the input power (in this
case, -7dBm). All units are in dBm.
8. To measure input 2
nd
order distortion, set the
Spectrum Analyzer start and stop frequencies to
2204MHz and 2206MHz, respectively. Sufficient
spectrum analyzer input attenuation should be used
to avoid distortion in the instrument.
9. The 2
nd
order intercept point is equal to P
1
– P
2
+ P
in
,
where P
1
is the power level of the fundamental
output tone at 1950MHz, P
2
is the 2
nd
order product
at 2205MHz, and P
in
is the input power (in this case,
-7dBm). All units are in dBm.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 642
HIGH LINEARITY UPCONVERTING MIXER
3
Figure 1. Proper Measurement Equipment Setup

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 642
HIGH LINEARITY UPCONVERTING MIXER
4

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