DC365 - LT5503 Evaluation Kit Quick Start Guide

August 02, 2001.
Demo board DC365A Quick Start Guide.
I. Introduction
The DC365A demo board is intended to demonstrate the capabilities of the LT5503 RF transmitter
IC. This IC incorporates a 1.2 GHz to 2.7 GHz direct I/Q modulator and a 1.7GHz to 2.7GHz mixer.
The LT5503 IC operates over a wide supply voltage range, from 5.25V down to 1.8V, and is
compatible with the LTC family of WLAN products.
The LT5503 (Figure 1) contains a high frequency quadrature modulator with a variable gain
amplifier (VGA), and a balanced up-converting mixer. The modulator includes a precision 90° phase
shifter which allows direct modulation of an RF signal by the baseband I and Q signals. Depending
on transceiver architecture and other considerations, the up-converting mixer can be used to generate
the high-frequency RF input for the modulator by mixing the system’s 1st and 2nd local oscillators.
The LT5503 modulator output can deliver up to -3dBm at 2.5GHz. The VGA allows output power
reduction in three steps, up to 15dB with two control pins. The baseband inputs are internally biased
for maximum input voltage swing at low supply voltage. If needed, they can be driven with external
bias voltages.
BPF
VCC2
2V
C22
1000p
Up mixer
Enable
Modulator
Enable
LO2IN
C12
1000p
VccLO2
C20
1000p
BQ+ BQ-
L3
2.7nH
MX-
VccLO1
MX+
MIXEN
VCC1
2V
VccRF VccMOD
C1
2p
MODRFIN
VGA
0°
÷1
C7
8p
VccVGA
MODEN
÷2
R2
47
90°
R1
390
MODRFout
L1
15n
L2
2.2nH
2.45 GHz
Modulated
RF Out
CONTROL
LOGIC
DMODE
LO1
L4
3.3nH
GC1 GC2
BI+ BI-
Figure 1. LT5503 IC block diagram.
The DC365A demo board (Figure 2A & 2B) is intended to demonstrate the up-converting mixer and
an I/Q modulator independently or in a chain, with the up-converting mixer generating the highfrequency carrier signal for the modulator input. A transceiver application schematic for the upconverting mixer followed by the I/Q modulator is shown in Figure 3. A transceiver application
schematic for the direct I/Q modulator in conjunction with a direct conversion receiver is shown in
Figure 4. The demo board’s modulator input/output matching circuitry is optimized for 2.45 GHz
applications. The mixer LO1 input is optimized for 2075 MHz. The mixer LO2 input is broadband
without external matching circuitry. Values for 1.2 GHz and 1.9 GHz frequencies are available in the
application notes of the LT5503 data sheet.
1
Matching
circuit
I IN
Single ended
to differential
Converter
Circuit
LO1IN
LT5503 IC
MODRFOUT
÷2
LO2 IN
Q IN
MIXRFOUT
90
÷1
o
Matching
circuit
Σ
90o
Single ended
to differential
Converter
Circuit
Matching
circuit
Matching
circuit
MODRFIN
Figure 2A. Demo board DC365A block diagram.
Q IN
I IN
VCC4
GND
LT1807
V2
MODRFIN
LT1807
V1
VCC1
V4
MODRFOUT
V3
LT5503 IC
LO2 IN
LO1 IN
GND VCC2
1
2
3
4
5
6
VCC3
MIXRFOUT
Figure 2B. Demo board DC365A.
2
Rx BPF
0
Divide 1/2
90
LO
Buffer
LT5502
LT5500
2nd Rx LO &
Tx offset PLL
Main PLL
BPF
(2nd Rx LO=Rx IF x 2)
I
I
I/Q modulator
LO
Buffer
0
PA
driver
Divide 1/2
(or straight)
Tx Up
converter
90
LT5503
Control
Tx power control
Q Q
Figure 3. LT5503 transceiver implementation with super heterodyne receiver.
3
Direct conversion
receiver IC
0
90
Main PLL
I
I
I/Q modulator
0
PA
driver
Divide 1/2
(or straight)
Tx Up
converter
90
LT5503
Control
Tx power control
Q Q
Figure 4. LT5503 transceiver implementation with direct conversion receiver.
4
II. Applications and implementation issues.
I/Q inputs external circuitry (refer to demo board schematic).
The external I/Q input circuitry is provided to convert single ended input modulation signals to
differential signals to best utilize the differential I/Q inputs of the LT5503 IC. If desired by users, the
external I/Q input circuitry can be configured to provide single-ended to single ended buffering only.
In this case, capacitors C17 and C18 should be removed and capacitors C41 and C42 should be
placed on the demo board. C41 and C42 provide RF ground to unused I/Q ports.
Control signals for demo board dipswitch block (numbers marked on the body of the dipswitch):
1st
GC1
2nd
GC2
3d
4th
5th
DMODE
MixEN
ModEN
6th
not used
Modulator RF output power
least significant bit of modulator output
power control
most significant bit of modulator output
power control
LOGIC STATE
Mixer 2nd LO divider mode control
Mixer Enable
Modulator Enable
Maximum
LOW
-4.5 dB
HIGH
-9.0 dB
LOW
-13.5 dB
HIGH
LOW
LOW
HIGH
HIGH
LOW
DIVIDE-BY-2
MIXER DISABLED
MODULATOR
DISABLED
HIGH
DIVIDE-BY-1
MIXER ENABLED
MODULATOR
ENABLED
III. LT5503 up converting mixer basic tests and measurements for 2.45 GHz
band. NOTE: 2.45 GHz demo board version should be used.
1. Connect all the test equipment and power supplies as shown on Figure 5.
2. Set power supply #2 and power supply #3 to desired supply voltage from 1.8 to 5.25 volts.
NOTE: One power supply can be used if desired.
3. Set dipswitch #4 to logic state LOW. Mixer is in OFF state. Measure supply current for
mixer OFF state.
4. Set dipswitch #4 to logic state HIGH. Mixer is in ON state. Measure supply current for
mixer ON state.
5. Set dipswitch #3 to logic state LOW for divide-by-2 setting for LO2 input. Set Signal
Generator 2 for F = 750 MHz, Pout = -18 dBm CW signal.
6. Set Signal Generator #1 for F = 2075 MHz, Pout = -12 dBm CW signal.
7. Set Spectrum Analyzer for center frequency 2450 MHz. Perform mixer conversion gain
and LO1/LO2 leakage measurements. Repeat measurements with different RF input
power levels for LO1 and LO2 ports.
8. Set dipswitch #3 to logic state HIGH for divide-by-1 setting for LO2 input. Set Signal
Generator 2 for F = 375 MHz, Pout = -18 dBm CW signal.
9. Repeat measurements of step 7.
5
IV. LT5503 up converting mixer basic tests and measurements for 1.9 GHz band.
NOTE: 1.9 GHz demo board version should be used.
1. Connect all the test equipment and power supplies as shown on Figure 5.
2. Set power supply #2 and power supply #3 to desired supply voltage from 1.8 to 5.25 volts.
NOTE: One power supply can be used if desired.
3. Set dipswitch #4 to logic state LOW. Mixer is in OFF state. Measure supply current for
mixer OFF state.
4. Set dipswitch #4 to logic state HIGH. Mixer is in ON state. Measure supply current for
mixer ON state.
5. Set dipswitch #3 to logic state LOW for divide-by-2 setting for LO2 input. Set Signal
Generator 2 for F = 480 MHz, Pout = -18 dBm CW signal.
6. Set Signal Generator #1 for F=1660 MHz, Pout = -12 dBm CW signal.
7. Set Spectrum Analyzer for center frequency 1900 MHz. Perform mixer conversion gain
and LO1/LO2 leakage measurements. Repeat measurements with different RF input
power levels for LO1 and LO2 ports.
8. Set dipswitch #3 to logic state HIGH for divide-by-1 setting for LO2 input. Set Signal
Generator 2 for F = 240 MHz, Pout = -18 dBm CW signal.
9. Repeat measurements of step 7.
6
Q IN
I IN
.
VCC4
GND
LT1807
V2
LT1807
V1
VCC1
V4
MODRFOUT
V3
LT5503 IC
MODRFIN
LO2 IN
LO1 IN
GND VCC2
1
2
3
4
5
6
Signal
Generator 2
VCC3
MIXRFOUT
+
Power Supply #3
Signal Generator 1
+
Spectrum Analyzer
Power Supply #2
Figure 5. Test set up for LT5503 up mixer measurements.
7
V. LT5503 I/Q modulator basic tests and measurements for 2.45 GHz band.
NOTE: 2.45 GHz demo board version should be used.
1. Connect all the test equipment and power supplies as shown on Figure 6.
2. Set power supply #4 to provide voltage from 3.5 to 5.25 volts.
NOTE: This power supply provides Vcc to two LT1807 op-amps ICs that perform single
ended to differential conversion for the LT5503 modulator differential I/Q inputs.
3. Set power supply #1 and power supply #3 to desired supply voltage from 1.8 to 5.25 volts.
NOTE: Single power supply can be used if desired to provide supply #1 and supply #3.
4. Set dipswitches #1 and #2 to logic state LOW/LOW (modulator maximum power output).
5. Set dipswitch #5 to logic state LOW. Modulator is in OFF state. Measure supply current for
modulator OFF state.
6. Set dipswitch #5 to logic state HIGH. Modulator is in ON state. Measure supply current for
modulator ON state.
7. Set Dual Signal Generator for F= 100 KHz, Vout = 500 mV p-p CW signals. Signal for I
o
channel should be programmed for 0 phase. Signal for Q channel should be programmed for
o
90 phase. NOTE: Dual Signal Generator should have 50-ohm output impedance.
8. Set Signal Generator for F = 2450 MHz, Pout = -16 dBm CW signal.
9. Set Spectrum Analyzer for center frequency 2450 MHz. Frequency span should be set for 1.0
MHz. Measure modulator RF output USB, LSB and Carrier signals. Repeat measurements
with different RF input power levels for MODIN.
10. Repeat measurements of step #9 for three other power output settings (dip switches #1 & #2
logic states LOW/HIGH, HIGH/LOW & LOW/LOW).
VI. LT5503 I/Q modulator basic tests and measurements for 1.9 GHz band.
NOTE: 1.9 GHz demo board version should be used.
1. Connect all the test equipment and power supplies as shown on Figure 6.
2. Set power supply #4 to provide voltage from 3.5 to 5.25 volts.
NOTE: This power supply provides Vcc to two LT1807 op-amps ICs that perform single
ended to differential conversion for LT5503 modulator differential I/Q inputs.
3. Set power supply #1 and power supply #3 to desired supply voltage from 1.8 to 5.25 volts.
4. Set dipswitches #1 and #2 to logic state HIGH/HIGH (modulator maximum power output).
5. Set dipswitch #5 to logic state LOW. Modulator is in OFF state. Measure supply current for
modulator OFF state.
6. Set dipswitch #5 to logic state HIGH. Modulator is in ON state. Measure supply current for
modulator ON state.
7. Set Dual Signal Generator for F= 100 KHz, Vout = 500 mV p-p CW signals. Signal for I
channel should be programmed for 0o phase. Signal for Q channel should be programmed for
90o phase. NOTE: Dual Signal Generator should have 50 ohm output impedance.
8. Set Signal Generator for F = 1900 MHz, Pout = -16 dBm CW signal.
9. Set Spectrum Analyzer for center frequency 1900 MHz. Frequency span should be set for 1.0
MHz. Measure modulator RF output USB, LSB and LO signals. Repeat measurements with
different RF input power levels for MODIN.
10. Repeat measurements of step #9 for three other power output settings (dip switches #1 & #2
logic states LOW/HIGH, HIGH/LOW & LOW/LOW).
8
+
Power Supply #4
0
90
o
+
-
o
Dual Signal
Generator
I IN
Power Supply #1
Q IN
VCC4
GND
LT1807
V2
Signal
Generator
LT1807
V1
Spectrum Analyzer
VCC1
V4
V4
LT5503 IC
V3
V4
MODRFOUT
MODRFIN
LO1 IN
LO2 IN
GND VCC2
1
2
3
4
5
6
VCC3
+
-
MIXRFOUT
Power Supply #3
Figure 6. Test set up for LT5503 I/Q modulator measurements.
9
VII. LT5503 up converting mixer and I/Q modulator (connected in chain) basic
tests and measurements for 2.45 GHz band.
NOTE: 2.45 GHz demo board version should be used.
1. Connect all the test equipment and power supplies as shown on Figure 7.
2. Set power supply #4 to provide voltage from 3.5 to 5.25 volts.
3. Set power supplies #1, #2 & #3 to desired supply voltage from 1.8 to 5.25 volts. NOTE: One
power supply can be used if desired for power supplies #1, #2 & #3. For tests with power
supply voltages 3.5 to 5.25 volts one power supply can be used if desired for power supplies
#1, #2, and #3 and power supply #4.
4. Set dipswitch #4 to logic state HIGH. Mixer is in ON state.
5. Set dipswitch #5 to logic state HIGH. Modulator is in ON state.
6. Set dipswitch #3 to logic state LOW for divide by 2 setting for LO2 input. Set Signal
Generator 2 for F = 750 MHz, Pout = -10 dBm CW signal.
7. Set Signal Generator #1 for F = 2075 MHz, Pout = -10 dBm CW signal.
8. Connect 3 dB attenuator pad between up converting mixer output and modulator input. If
desired, 2.45 GHz bandpass filter can be used instead to filter out mixing spurious products.
9. Set dipswitches #1 and #2 to logic state LOW/LOW (modulator maximum power output).
10. Set Dual Signal Generator for F= 100 KHz, Vout = 500 mV p-p CW signals. Signal for I
o
channel should be programmed for 0 phase. Signal for Q channel should be programmed for
o
90 phase. NOTE: Dual Signal Generator should have 50-ohm output impedance.
11. Set Spectrum Analyzer for center frequency 2450 MHz. Frequency span should be set for 1.0
MHz. Measure modulator RF output USB, LSB and LO signals.
12. Repeat measurements of step #11 for three other RF power output settings (dip switches #1 &
#2 logic states LOW/HIGH, HIGH/LOW & HIGH/HIGH).
10
+
0
Power Supply #4
o
+
90
o
Dual Signal
Generator
Q IN
I IN
Power Supply #1
VCC4
GND
LT1807
V2
LT1807
V1
Spectrum Analyzer
VCC1
V4
MODRFIN
V3
MODRFOUT
LT5503 IC
Signal Generator 2
LO2 IN
Signal
Generator 1
LO1 IN
GND VCC2
1
2
3
4
5
6
VCC3
-
MIXRFOUT
+
Power Supply #3
Power Supply #2
+
External 3 dB
Attenuator pad,
or 2.45 GHZ BPF
Figure 7. Test set up for LT5503 up converting mixer & I/Q modulator chain
measurements.
11