The In-Phase and Quadrature-Phase baseband signal (150MHz)
output from DAC are fed to the modulator TRF370317. The LO given to the
Modulator is 1.62GHz with 0dBm level from a clean source. The bias given to the
modulator is 1.7V and the resistors in the resistor divider, used to provide
this bias, are of 0.1% precision.
With this the results what we observed are,
1) Sideband suppression of 12dBc
As far as level at modulator input is considered, capacitors in
between the DAC and modulator will remove the DC, if any, on the DAC output,
before feeding it to the Modulator. At Modulator input we are shifting the
level to 1.7V, (as said in the datasheet [page no. 4]). The voltage levels at
the input point of modulator, as measured in the oscilloscope, are IVIN =
1.749V IREF = 1.752V, QVIN = 1.748V , QREF = 1.752V.
So the difference in the levels is 0.004V, which is negligible.
Here i am attaching you my schematics and layout for reference.
output level what we are targeting are
suppression of more than 50dBc.
2) Carrier suppression of more than 50dBm.
know how to improve the performance.
The sideband suppression performance can be improved by tuning the amplitude and phase between the I and Q ports. The carrier suppression can be improved by adjusting the DC offset between the I and the Q ports.
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