SC5313A Operating & Programming Manual
Rev 1.0.2
15
Selecting the LO Filter
LO_FILTER_SELECT (0x16)
– There are 9 RF filters to select from to improve LO input second harmonic
suppression. Bits [3:0] are used.
Enabling LO Output
LO_OUT_ENABLE (0x17)
– Setting bit 0 high enables the LO signal to be ported out the LO output
connector. Note there is always a leakage out of this port and the levels could be as high as -30 dBm. It is
recommended to terminate this port into a 50
W
load if it is not used.
Setting the IF Gain
IF_GAIN_DAC (0x18)
– Each of the channels has an adjustable IF amplifier with a step resolution of
0.25 dB per LSB. Writing the associated 6-bit DAC provides a gain range of 0 dB to 15.75 dB. Byte 1
selects the channel, while byte 0 determines the DAC value. A maximum DAC value of 63 will provide
maximum gain.
Setting the Common Output Voltage
VCOM_OUT_DAC (0x19)
– The common output voltage of each channel of differential amplifiers can be
adjusted by writing to this DAC. The output voltage is linear in the region of 1.0 V to 3.5 V and follows
the equation:
Removing DC Offset in Differential Amplifiers
DC_OFFSET_DAC (0x1A)
– The DC offset between the (+) and (-) terminals of the differential amplifier
output can be minimized by writing this DAC. Varying the DAC value from 0 to 16383 can correct up to
approximately
of DC offset error. This correction resolution is less than 0.01 mV per LSB. An
approximation of the DAC value to offset voltage is given below.
Setting the Output Linearity of the IQ Demodulator
LINEARITY_DAC (0x19)
– This DAC controls the current draw of the IQ modulator. As rule of thumb, the
more current, the better the linearity. However, the user may find that the linearity can be improved
with slight adjustments to the current consumption. The linearity is additionally dependent on the
operating frequency and input RF power levels. Typically, the DAC is set around 4.5 V using the following
equation:
