DEMO CIRCUIT 1431A-A
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LTC5540
600MHz to 1.3GHz
HIGH DYNAMIC RANGE DOWNCONVERTING MIXER
DESCRIPTION
Demonstration Circuit 1431A-A is a 600MHz to
1.3GHz high dynamic range downconverting mixer
featuring the LTC
®
5540. The LTC5540 is part of a
family of high dynamic range, passive downcon-
verting mixers covering the 600MHz to 4GHz fre-
quency range.
The Demo Circuit 1431A-A and
the LTC5540 are optimized for 600MHz to
1.3GHz RF applications. The LO frequency
must fall within the 700MHz to 1.2GHz range for
optimum performance.
The LTC5540 is designed for 3.3V operation, how-
ever the IF amplifier can be powered by 5V for the
highest P1dB. An integrated SPDT LO switch with
fast switching accepts two active LO signals, while
providing high isolation.
The LTC5540’s high conversion gain and high dy-
namic range enable the use of lossy IF filters in
high-selective receiver designs, while minimizing
the total solution cost, board space and system-
level variation.
High Dynamic Range Downconverting Mixer Family
RF RANGE
LO RANGE
DEMO #
IC PART #
DC1431A-A LTC5540 600MHz-1.3GHz 700MHz-1.2GHz
DC1431A-B
LTC5541
1.3GHz-2.3GHz
1.4GHz-2.0GHz
DC1431A-C
LTC5542
1.6GHz-2.7GHz
1.7GHz-2.5GHz
DC1431A-D
LTC5543
2.3GHz-4.0GHz
2.4GHz-3.6GHz
Design files for this circuit board are available. Call
the LTC factory.
, LT, LTC, LTM, Linear Technology and the Linear Logo are registered trade-
marks of Linear Technology Corporation. All other trademarks are the property of
their respective owners.
TABLE 1. TYPICAL PERFORMANCE SUMMARY
T
A
= 25°C, V
CC
= 3.3V, V
CCIF
= 3.3V, SHDN = Low, P
LO
= 0dBm, P
RF
= -3dBm (∆f = 2MHz for two-tone IIP3 tests), unless otherwise noted.
PARAMETER
V
CC
Supply Voltage Range
V
CCIF
Supply Voltage Range
Total Supply Current (V
CC
+ V
CCIF
)
Total Supply Current During Shutdown
SHDN Input Low Voltage (IC On)
SHDN Input High Voltage (IC Off)
LOSEL Input Low Voltage (LO1 Selected)
LOSEL Input High Voltage (LO2 Selected)
LO Input Frequency Range
LO Input Return Loss
LO Input Power Range
RF Input Frequency Range
RF Input Return Loss
Z
0
= 50Ω, f
LO
= 700MHz to 1200MHz
f
LO
= 700MHz to 1200MHz
Low-Side LO
High-Side LO
Z
0
= 50Ω, f
RF
= 600MHz to 1300MHz
SHDN = High
CONDITIONS
VALUE
3.1 to 3.5
3.1 to 5.3
193
≤
500
< 0.3
>3
< 0.3
>3
700 to 1200
> 12
-4 to 6
800 to 1300
600 to 1100
> 12
UNITS
V
V
mA
µA
V
V
V
V
MHz
dB
dBm
MHz
dB
1
LTC5540
TYPICAL PERFORMANCE SUMMARY, CONTINUED
T
A
= 25°C, V
CC
= 3.3V, V
CCIF
= 3.3V, SHDN = Low, P
LO
= 0dBm, P
RF
= -3dBm (∆f = 2MHz for two-tone IIP3 tests), unless otherwise noted.
IF Output Frequency
190
MHz
(Can be re-matched for other frequencies.)
IF Output Return Loss
LO to RF Leakage
LO to IF Leakage
LO Switch Isolation
RF to LO Isolation
RF to IF Isolation
PARAMETER
Conversion Gain
f
LO
= 700MHz to 1200MHz
f
LO
= 700MHz to 1200MHz
LO1 Selected, 700MHz < f
LO
< 1200MHz
LO2 Selected, 700MHz < f
LO
< 1200MHz
f
RF
= 600MHz to 1300MHz
f
RF
= 600MHz to 1300MHz
CONDITIONS
RF = 900MHz
RF = 1100MHz
RF = 1300MHz
RF = 900MHz
RF = 1100MHz
RF = 1300MHz
RF = 900MHz
RF = 1100MHz
RF = 1300MHz
f
RF
= 900MHz, f
LO
= 710MHz
f
BLOCK
= 1000MHz, P
BLOCK
= 5dBm
f
RF
= 805MHz at -10dBm, f
LO
= 710MHz
f
RF
= 773.33MHz at -10dBm, f
LO
= 710MHz
RF = 900MHz, V
CCIF
= 3.3V
RF = 900MHz, V
CCIF
= 5V
CONDITIONS
RF = 700MHz
RF = 900MHz
RF = 1100MHz
RF = 700MHz
RF = 900MHz
RF = 1100MHz
RF = 700MHz
RF = 900MHz
RF = 1100MHz
f
RF
= 900MHz, f
LO
= 1090MHz
f
BLOCK
= 800MHz, P
BLOCK
= 5dBm
f
RF
= 995MHz at -10dBm, f
LO
= 1090MHz
f
RF
= 1026.67MHz at -10dBm, f
LO
= 1090MHz
RF = 900MHz, V
CCIF
= 3.3V
RF = 900MHz, V
CCIF
= 5V
> 12
< -30
< -37
> 50
> 47
> 55
> 37
VALUE
7.0
7.8
8.0
24.4
24.1
23.6
10.6
10.5
10.3
16.7
-61.5
-68
11
14
VALUE
7.6
7.9
7.9
26.5
25.9
23.8
10.0
9.9
10.4
16.2
-70
-75
11
14.5
dB
dBm
dBm
dB
dB
dB
UNITS
dB
Low-Side LO Downmixer Application: RF = 800MHz to 1300MHz, IF = 190MHz, f
LO
= f
RF
– f
IF
Input 3 Order Intercept
rd
dBm
SSB Noise Figure
dB
SSB Noise Figure Under Blocking
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
dB
dBc
dBc
dBm
High-Side LO Downmixer Application: RF = 600MHz to 1100MHz, IF = 190MHz, f
LO
= f
RF
+ f
IF
PARAMETER
Conversion Gain
UNITS
dB
Input 3 Order Intercept
rd
dBm
SSB Noise Figure
dB
SSB Noise Figure Under Blocking
2LO – 2RF Output Spurious Product
(f
RF
= f
LO
– f
IF
/2)
3LO – 3RF Output Spurious Product
(f
RF
= f
LO
– f
IF
/3)
Input 1dB Compression
dB
dBc
dBc
dBm
2
LTC5540
APPLICATIONS NOTE
For detailed applications information, please refer
to the LTC5540 datasheet.
TABLE 2. SHDN LOGIC TABLE
SHDN
Low
High
IC STATE
On
Off
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.
LO SWITCH
The LTC5540 features an integrated SPDT
switch designed for high isolation and fast
(<50ns) switching. The LO switch is controlled
by the LOSEL logic control. The LOSEL must be
pulled Low or High. If left floating, the LO selection
will be indeterminate. A logic table for the LO
switch is shown in Table 3.
TABLE 3. LO SWITCH LOGIC TABLE
LOSEL
ACTIVE LO INPUT
Low
LO1
High
LO2
Mixer Supply Voltage (V
CC1
, V
CC2
)...........................3.8V
LO Switch Supply Voltage (V
CC3
)..............................3.8V
IF Supply Voltage (IF+, IF-) ........................................5.5V
Shutdown Voltage (SHDN)................ -0.3V to V
CC
+ 0.3V
LO Select Voltage (LOSEL) .............. -0.3V to V
CC
+ 0.3V
LO1, LO2 Input Power (0.2GHz to 2GHz) ................9dBm
LO1, LO2 Input DC Voltage .....................................±0.5V
RF Input Power (0.2GHz to 2GHz).........................15dBm
RF Input DC Voltage ............................................... ±0.1V
Operating Temperature Range.................... -40° to 85°
C
C
RF INPUT
The RF input of Demonstration Circuit 1431A-A
is matched to 50Ω from 600MHz to 1.3GHz with
better than 12dB return loss.
For the RF input
to be matched, the selected LO input must be
driven.
The RF input impedance is somewhat
dependent on LO frequency and, to a lesser ex-
tend, LO input power.
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 VCC_IF tur-
rets.
Instead, make all necessary connections with
power supplies turned off, then increase to operat-
ing voltage.
LO INPUTS
The LTC5540’s LO amplifiers are optimized for
the 700MHz to 1.2GHz LO frequency range. LO
frequencies above and below this frequency
range may be used with degraded performance.
The LO1 and LO2 inputs are always 50Ω-
matched when V
CC
is applied to the chip, even
when the chip is shutdown. The DC resistance
of the selected LO input is approximately 23Ω,
and the unselected input is approximately 50Ω.
The nominal LO input level is 0dBm. The LO
input power range is between -4dBm and 6dBm.
LO input power greater than 6dBm may cause
conduction of the internal ESD diodes and
should be avoided.
SHUTDOWN FEATURE
When the SHDN voltage is logic Low (<0.3V), the
chip is enabled. When the SHDN voltage is logic
High (>3V), the chip is disabled, and the current
consumption is reduced to below 500µA. The
SHDN must be pulled Low or High. If left floating,
the On/Off state of the IC will be indeterminate. A
logic table for the SHDN is shown in Table 2.
3
LTC5540
IF OUTPUT
Demonstration Circuit 1431A-A features a sin-
gle-ended, 50Ω-matched IF output for 190MHz.
The impedance matching is realized with a
bandpass topology using an IF transformer as
shown in Figure 1.
For IF frequencies below 70MHz, the values of
L1 and L2 become unreasonably high, and the
lowpass topology shown in Figure 3 is preferred.
See the LTC5540 datasheet for details.
Figure 3. IF Output with Lowpass Matching
Figure 1. IF Output with Bandpass Matching
Demonstration Circuit 1431A-A can be easily re-
configured for other IF frequencies by simply re-
placing inductors L1 and L2. L1 and L2 values
for several common IF frequencies are pre-
sented in Table 4, and return losses are plotted
in Figure 2.
TABLE 4. L1, L2 vs. IF FREQUENCIES
IF FREQUENCY (MHz)
140
190
240
380
450
L1, L2 (nH)
270
150
100
33
22
Demonstration Circuit 1431A-A’s IF output can
be converted to lowpass matching with minimal
modifications. Follow the procedures below,
and refer to Figure 4.
a.
b.
c.
d.
e.
f.
Remove existing L1, L2, and C10.
Cut the traces leading to the IF transformer
close to the pads of L1 and L2.
Insert series inductors on the cut traces.
Install a 0Ω jumper between the pads of C8
and C10.
Install R2 at location R2.
Install C13 next to, or on top of, R2.
Figure 2. IF Output Return Loss
Figure 4. Modifications for Lowpass Matching
4
LTC5540
MEASUREMENT EQUIPMENT
AND SETUP
The LTC5540 is a high dynamic range downcon-
verting mixer IC with very high input 3rd order
intercept. Accuracy of its performance meas-
urement is highly dependent on equipment
setup and measurement technique. The rec-
ommended measurement setups are presented
in Figure 5, Figure 6, and Figure 7. The follow-
ing 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 Mini-
Circuits 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 re-
flections, 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 ana-
lyzer 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 de-
signed to operate at their best with about
-30dBm at their input filter or preselector. Suffi-
cient spectrum analyzer input attenuation
should be used to avoid saturating the instru-
ment, but too much attenuation reduces sensi-
tivity and dynamic range.
8.
Before taking measurements, the system per-
formance 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.
The spectrum analyzer’s internal distortion
is minimized.
The spectrum analyzer has enough dy-
namic range and sensitivity. The meas-
urement system’s IIP3 should be at least
15dB better than the DUT’s OIP3.
The system is accurately calibrated for
power and frequency.
b.
c.
d.
A SPECIAL NOTE ABOUT RF TERMINATION
The LTC5540 consists of a high linearity passive
double-balanced mixer core and IF buffer ampli-
fier. Due to the bi-directional nature of all pas-
sive mixers, LO±IF mixing product is always pre-
sent at the RF input, typically at a level of 12dB be-
low the RF input signal. If the LO±IF “Pseudo-
Image Spur” is not properly terminated, it may in-
terfere with the source signals, and can degrade
the measured linearity and noise figure signifi-
cantly. To avoid interference from the LO±IF
“Pseudo-Image Spur”, terminate the RF input port
with an isolator, diplexer, or attenuator. In the rec-
ommended measurement setups presented in
Figure 6 and Figure 7, the 6dB attenuator pad at
the demonstration circuit’s RF input serves this
purpose.
5
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