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dc2391af
DEMO MANUAL DC2391A
NOTES ON TEST EQUIPMENT AND SETUP
QUICK START PROCEDURE
• Use a high performance baseband signal genera-
tor with differential outputs, such as the Rohde &
Schwarz SMJ100A vector signal generator or
equivalent.
• The LO harmonics can degrade image rejection
severely. Third harmonic should be kept at least 6dB
lower than the desired image rejection, or it should
be compensated by adjusting the quadrature phase
balance, register 0x05. In the extreme case of nearly
square wave LO drive, large offset values may be
required for registers 0x04 and 0x05.
• Use narrow resolution bandwidth (RBW) and engage
video averaging on the spectrum analyzer to lower
the displayed average noise level (DANL). The trade-
off is increased sweep time.
• Spectrum analyzers can produce significant internal
distortion products if overdriven. Generally, spectrum
analyzers are designed to operate their best with
about –30 to –40dBm at their 1st mixer. Sufficient
spectrum analyzer input attenuation should be used
to avoid overdrive, but too much attenuation reduces
sensitivity and dynamic range.
• Before taking measurements, the system performance
should be evaluated to ensure that: 1) clean baseband
signals can be produced, 2) the LO harmonics and
phase noise are minimized for CW LO drive, 3) the
spectrum analyzer’s internal distortion is minimized,
and noise floor is satisfactory.
1. Remove the DC2391A from its protective packaging in
an ESD-safe working area (see Figure 1). Make sure
jumper JP1 is installed (V
CTRL
= V
CC
).
2. Set the baseband signal generator output DC common-
mode voltage to +1.4VDC, set the amplitude (V
emf
) = 1V
diff, but do not yet connect the 4 cables to the DC2391A.
3. Connect the DC power supply and increase voltage
to +3.3V. Using a voltmeter, verify the voltage at the
LTC5589 V
CC
pin or JP1 is +3.3V. Adjust if necessary.
4. Apply
3.3V to DC2391A’s enable input (EN).The enable
voltage must never exceed the LTC5589’s V
CC
supply
voltage by 0.3V or drop below –0.3V.
5. Verify the total V
CC
supply current is approximately
29mA.
6. Connect the RF output to the spectrum analyzer.
7. Connect the LO source to the LO input and apply a
2560MHz, 0dBm CW LO signal.
8. Configure the baseband signal source to provide a
single CW carrier with 100kHz offset. I- and Q-channels
should be in phase-quadrature and set for lower side-
band selection.
9. Observe the modulator’s RF output on the spectrum
analyzer at 2559.9MHz. Also observe the sideband
suppression (aka Image Rejection) at 2560.1MHz,
and the LO Leakage at 2560MHz.
10. Up to this point, the I/Q Modulator has been at default
center frequency and gain, with no trims. To change
modulator center frequency, gain, etc., connect the
Linduino to the DC2391A with the ribbon cable pro-
vided. Make sure jumper JP3 on the DC2026C is set
to 3.3V.
11. Run QuikEval
™
to start the GUI associated with the I/Q
modulator.
12. Be sure to update the QuikEval to get latest software
version that supports the LTC5589. LTC5589 GUI will
automatically be installed on the computer for the
first time when DC2391A is connected to Linduino
DC2026C.
13. The turn off procedure is the reverse of the turn on
procedure: Make sure V
EN
is removed before V
CC
.
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