SIGNALCORE SC5312A User Manual page 13

12 SC5312A & SC5313A Hardware Manual
The RF amplifiers are used to improve the gain of the device if the input signal is too low or when the losses
at higher frequencies are large. RF AMP#1 is usually selected when the RF signals are lower than -25 dBm
at the input port. With RF AMP#1 enabled, the device sensitivity is improved and the detection of low level
signals is better resolved. RF AMP#2 should be selected and switched into the signal path at RF frequencies
greater than 5 GHz, where the signal power loss through the front end prior to the demodulator can be as
high as 15 dB due to filter and switch insertion losses. At these high RF frequencies, if the IF gain is at its
maximum of 15.75 dB (DAC code = 63) and the IF output level falls below -10 dBm or outside the digitizer's
optimal levels, RF AMP#2 should be enabled.
RF Amp
#1
RF Atten
#1
Figure 1. Block diagram of the signal conversion module of the downconverter assembly
The RF attenuators provide attenuation when required. RF ATTEN#1 attenuation should be stepped up as
the signal power at the RF port increases above -10 dBm. Nonlinear components of the signal such as IMD3
and second order harmonics will increase in magnitude as the input signal increases; therefore the user
should exercise good judgment to determine when to use RF ATTEN#1. Do not over-attenuate. Doing so
will negatively impact the signal-to-noise ratio.
RF ATTEN#2 is used when the input signal needs further suppression to improve linearity. It should also be
used if RF AMP#1 is enabled to improve sensitivity, but as a result the level at the input of RF AMP#3 (always
in the path) may be too high. Step up the attenuation of RF ATTEN#2 to ensure the system (resulting from
RF AMP#3) is not driven too hard. Finally RF ATTEN#3 is used to control the level to the IQ demodulator
when RF AMP#2 is enabled (switched into the signal path).
Rev 2.1 | SC5312A & SC5313A
Demodulator
RF Amp
#3
RF Atten
RF Atten
#3
#2
9 Selectable
RF Filters
LO Amp
#1
User Manual
DC
5V Vocm
Offset
Ref Dac
DAC
Vocm
Linearity
2.5V
Dac
Ref
i+
IQ
i-
RF Amp
#2
LO Amp
#2
9 Selectable
LO Filters
Variable Out Diff
Diff Amp Amp
i+
50
Vocm Vocm
50
i-
Gain
90
Selectable
0
IF Diff_Amp
SignalCore, Inc.