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DESCRIPTION
Demonstration Circuit 1710A-D is a dual 2.3GHz to
4.5GHz high dynamic range downconverting mixer
featuring the LTC®5593. The LTC5593 is part of a
family of dual-channel high dynamic range, high
gain downconverting mixers covering the 600MHz
to 4.5GHz frequency range.
The Demo Circuit
1710A-D and the LTC5593 are optimized for
2.3GHz to 4.5GHz RF applications. The LO frequency must fall within the 2.1GHz to 4.2GHz
range for optimum performance.
A typical application is a LTE or WiMAX multichannel or diversity
receiver with a 2.3GHz to 2.7GHz RF input.
The LTC5593 is designed for 3.3V operation, however the IF amplifiers can be powered by 5V for the
highest P1dB. A low current mode is provided for
power savings, and each of the mixer channels
has independent shutdown control.
The LTC5593’s high conversion gain and high dynamic range enable the use of lossy IF filters in
high-selective receiver designs, while minimizing
the total solution cost, board space and systemlevel variation.
High Dynamic Range Dual Downconverting Mixer Family
DEMO # IC PART # RF RANGE LO RANGE
DC1710A-A LTC5590 600MHz-1.7GHz 700MHz-1.5GHz
DC1710A-B LTC5591 1.3GHz-2.3GHz 1.4GHz-2.1GHz
DC1710A-C LTC5592 1.6GHz-2.7GHz 1.7GHz-2.5GHz
DC1710A-D LTC5593 2.3GHz-4.5GHz 2.1GHz-4.2GHz
Design files for this circuit board are available. Call
the LTC factory.
, LT, LTC, LTM, Linear Technology and the Linear Logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of
their respective owners.
DEMO CIRCUIT 1710A-
D
QUICK START GUIDE
LTC559
3
Dual 2.3GHz to 4.5
GHz
HIGH DYNAMIC RANGE
DOWNCONVERTING MIXER
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LTC5593
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APPLICATIONS NOTE
For detailed applications information, please refer
to the LTC5593 datasheet.
ABSOLUTE MAXIMUM RATINGS
NOTE.
Stresses beyond Absolute Maximum Ratings may cause
permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Supply Voltage (VCC)
.............................................4.0V
IF Supply Voltage (VCCIF)
......................................
5.5V
Enable Voltage (ENA, ENB)
.............
-0.3V to V
CC
+ 0.3V
Bias Adjust Voltage (IFBA, IFBB)
......
-0.3V to V
CC
+ 0.3V
Power Select Voltage (ISEL)
.............
-0.3V to V
CC
+ 0.3V
LO Input Power (1GHz to 3GHz)
...........................
9dBm
RFA, RFB Input Power (1GHz to 3GHz)
................
15dBm
Operating Temperature Range
.................
-40°C to 105°C
SUPPLY VOLTAGE RAMPING
Fast ramping of the supply voltage can cause a
current glitch in the internal ESD protection circuits.
Depending on the supply inductance, this could
result in a supply voltage transient that exceeds the
maximum rating. A supply voltage ramp time of
greater than 1ms is recommended.
Do not clip powered test leads directly onto the
demonstration circuit’s VCC and VCCIF turrets.
Instead, make all necessary connections with
power supplies turned off, then increase to operating voltage.
ENABLE FUNCTION
The LTC5593’s two mixer channels can be independently enabled or disabled. When the Enable
voltage (ENA or ENB) is logic high (>2.5V), the corresponding mixer channel is enabled. When the
Enable voltage is logic low (<0.3V), the mixer
channel is disabled. The voltages at the enable
pins should never fall below -0.3V or exceed the
power supply voltage by more than 0.3V. The En-
able pins must be pulled high or low. If left floating,
the on/off state of the IC will be indeterminate. A
logic table for the Enable control (ENA, ENB) is
shown in Table 1.
TABLE 1. ENABLE CONTROL LOGIC TABLE
ENA, ENB MIXER CHANNEL STATE
Low Disabled
High Enabled
LOW CURRENT MODE
The LTC5593 features a low current mode, which
allows the flexibility to choose a 37% total power
saving when lower RF performance is acceptable.
When the ISEL voltage is logic low (<0.3V), both
mixer channels operate at nominal DC current and
best performance. When the ISEL voltage is logic
high (>2.5V), both mixer channels are in low current mode and operate with reduced performance.
The ISEL voltage should never fall below -0.3V or
exceed the power supply voltage by more than
0.3V. The ISEL pin must be pulled low or high. If
left floating, the operating current state of the IC will
be indeterminate. A logic table for ISEL is shown in
Table 2.
TABLE 2. ISEL LOGIC TABLE
ISEL OPERATING MODE
Low Normal current, best performance
High Low current, reduced performance
RF INPUTS
Demonstration Circuit 1710A-D’s RF inputs of
channel A and channel B are identical.
For the RF
inputs to be matched, the appropriate LO signal must be applied.
The RF inputs’ impedance is
dependent on LO frequency, but the Demonstration Circuit 1710A-D’s RF inputs are well matched
to 50Ω from 2.3GHz to 4.5GHz, with better than
12dB return loss, when a 2.1GHz to 4.2GHz LO
signal is applied.
LO INPUTS
Demonstration Circuit 1710A-D’s LO input is well
matched to 50
Ω
from 2.1GHz to 3.4GHz, with bet-
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LTC5593
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ter than 12dB return loss. For LO frequency from
3.4GHz to 3.8GHz, the LO port can be well
matched by using C2 = 0.6pF and L4 = 10nH.
The LTC5593’s LO amplifiers are optimized for the
2.1GHz to 4.2GHz LO frequency range. LO frequencies above and below this frequency range
may be used with degraded performance. The LO
input is always 50Ω-matched when VCC is applied
to the chip, even when one or both of the channels
is disabled. The nominal LO input level is 0dBm.
The LO input power range is between -4dBm and
6dBm.
IF OUTPUT
Demonstration Circuit 1710A-D features singleended, 50Ω-matched IF outputs for 190MHz. The
channel A and the channel B IF outputs are identical, and the impedance matching is realized with a
bandpass topology using IF.
Demonstration Circuit 1710A-D can be easily reconfigured for other IF frequencies by simply replacing inductors L1A, L2A, L1B and L2B. Inductor
values for several common IF frequencies are presented in Table 3. External load resistor, R2A and
R2B, can be used to improve impedance matching
if desired.
TABLE 3. INDUCTOR VALUES vs. IF FREQUENCIES
IF FREQUENCY (MHz) L1A, L2A, L1B, L2B (nH)
140 270
190 150
240 100
300 56
380 33
470 22
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MEASUREMENT EQUIPMENT
AND SETUP
The LTC5593 is a dual high dynamic range downconverting mixer IC with very high input 3rd order
intercept. Accuracy of its performance measurement is highly dependent on equipment setup and
measurement technique. The recommended
measurement setups are presented in Figure 5,
Figure 6, and Figure 7. The following precautions
should be observed:
1.
Use high performance signal generators with
low harmonic output and low phase noise, such
as the Rohde & Schwarz SME06. Filters at the
signal generators’ outputs may also be used to
suppress higher-order harmonics.
2.
A high quality RF power combiner that provide
broadband 50Ω-termination on all ports and
have good port-to-port isolation should be
used, such as the MCLI PS2-17.
3.
Use high performance amplifiers with high IP3
and high reverse isolation, such as the MiniCircuits ZHL-1042J, on the outputs of the RF
signal generators to improve source isolation to
prevent the sources from modulating each
other and generating intermodulation products.
4.
Use attenuator pads with good VSWR on the
demonstration circuit’s input and output ports to
improve source and load match to reduce reflections, which may degrade measurement
accuracy.
5.
A high dynamic range spectrum analyzer, such
as the Rohde & Schwarz FSEM30, should be
used for linearity measurement.
6.
Use narrow resolution bandwidth (RBW) and
engage video averaging on the spectrum analyzer to lower the displayed average noise level
(DANL) in order to improve sensitivity and to
increase dynamic range. However, the trade off
is increased sweep time.
7.
Spectrum analyzers can produce significant
internal distortion products if they are over-
driven. Generally, spectrum analyzers are designed to operate at their best with about
-30dBm at their input filter or preselector. Sufficient spectrum analyzer input attenuation
should be used to avoid saturating the instrument, but too much attenuation reduces sensitivity and dynamic range.
8.
Before taking measurements, the system performance should be evaluated to ensure that:
a.
Clean input signals can be produced. The
two-tone signals’ OIP3 should be at least
15dB better than the DUT’s IIP3.
b.
The spectrum analyzer’s internal distortion
is minimized.
c.
The spectrum analyzer has enough dynamic range and sensitivity. The measurement system’s IIP3 should be at least 15dB
better than the DUT’s OIP3.
d.
The system is accurately calibrated for
power and frequency.
A SPECIAL NOTE ABOUT RF TERMINATION
The LTC5593 consists of high linearity passive
double-balanced mixer cores and IF buffer amplifiers. Due to the bi-directional nature of all passive
mixers, LO±IF mixing product is always present at
the RF input, typically at a level of 12dB below the
RF input signal. If the LO±IF “Pseudo-Image Spur”
is not properly terminated, it may interfere with the
source signals, and can degrade the measured
linearity and noise figure significantly. To avoid interference from the LO±IF “Pseudo-Image Spur”,
terminate the RF input port with an isolator, diplexer, or attenuator. In the recommended measurement setups presented in Figure 6 and Figure
7, the 6dB attenuator pad at the demonstration circuit’s RF input serves this purpose.
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QUICK START PROCEDURE
Demonstration circuit
1710A-D
is easy to set up to
evaluate the performance of the LTC
5593
. Refer to
Figure 1, Figure 2, and Figure 3 for proper equipment connections. The following procedures describe performing measurements on Mixer Channel A. The measurement procedures for Mixer
Channel B are identical.
NOTE.
Care should be taken to never exceed absolute maximum
input ratings. Make all connections with RF and DC power off.
RETURN LOSS MEASUREMENTS
1.
Configure the Network Analyzer for return loss
measurement, set appropriate frequency
range, and set the test signal to -3dBm.
2.
Calibrate the Network Analyzer.
3.
Connect all test equipment as shown in Figure
5 with the signal generator and the DC power
supply turned off.
4.
Increase the DC power supply voltage to 3.3V,
and verify that the total current consumption is
close to the figure listed in the Typical Demonstration Circuit Performance Summary. The
supply voltage should be confirmed at the
demo board VCC, VCCIF and GND terminals
to account for lead ohmic losses.
5.
With the LO signal applied, and all unused
demo board ports terminated in 50Ω, measure
return losses of the RFA input and IFA output
ports.
6.
Set the test signal to 0dBm, and re-calibrate the
Network Analyzer.
7.
Terminate all unused demo board ports in 50Ω.
Measure return losses of the LO input port.
RF PERFORMANCE MEASUREMENTS
1.
Connect all test equipment as shown in Figure
6 with the signal generators and the DC power
supply turned off.
2.
Increase the DC power supply voltage to 3.3V,
and verify that the total current consumption is
close to the figure listed in the Typical Demonstration Circuit Performance Summary. The
supply voltage should be confirmed at the
demo board VCC, VCCIF and GND terminals
to account for lead ohmic losses.
3.
Set the LO source (Signal Generator 1) to provide a 0dBm CW signal at appropriate LO frequency to the demo board LO input port.
4.
Set the RF sources (Signal Generators 2 and
3) to provide two -3dBm CW signals, 2MHz
apart, at the appropriate RF frequencies to the
demo board RFA input port.
5.
Measure the resulting IFA output on the Spectrum Analyzer:
a.
The wanted two-tone IF output signals are
at:
f
IF1
= f
RF1
- fLO, and
f
IF2
= f
RF2
- fLO for low-side LO,
and
f
IF1
= fLO - f
RF1
, and
f
IF2
= fLO - f
RF2
for high-side LO
b.
The 3rd order intermodulation products
which are closest to the wanted IF signals
are used to calculate the Input 3rd Order Intercept:
f
IM3,1
= f
RF1
- fLO - ∆IF, and
f
IM3,2
= f
RF2
- fLO + ∆IF for low-side LO,
and
f
IM3,1
= fLO - f
RF1
+ ∆IF, and
f
IM3,2
= fLO - f
RF2
- ∆IF for high-side LO
Where
∆IF = f
RF2
- f
RF1
.
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6.
Calculate Input 3rd Order Intercept:
IIP3 = (∆
IM3
)/2 + P
RF
Where
∆
IM3
= PIF - P
IM3
. PIF is the lowest IF
output signal power at either f
IF1
or f
IF2
. P
IM3
is
the highest 3rd order intermodulation product
power at either f
IM3,1
or f
IM3,2
. PRF is the per-
tone RF input power.
7.
Turn off one of the RF signal generators, and
measure Conversion Gain, RF to IF isolation,
LO to IF leakage, and Input 1dB compression
point.
NOISE FIGURE MEASUREMENT
1.
Configure and calibrate the noise figure meter
for mixer measurements.
2.
Connect all test equipment as shown in Figure
7 with the signal generator and the DC power
supply turned off.
3.
Increase the DC power supply voltage to 3.3V,
and verify that the total current consumption is
close to the figure listed in the Typical Demonstration Circuit Performance Summary. The
supply voltage should be confirmed at the
demo board VCC, VCCIF and GND terminals
to account for lead ohmic losses.
4.
Measure the single-sideband noise figure.
Figure 1. Proper Equipment Setup for Return Loss Measurements
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Figure 2. Proper Equipment Setup for RF Performance Measurements
Figure 3. Proper Equipment Setup for Noise Figure Measurement
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Figure 4. Demonstration Circuit schematic
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