SC5305A Operating & Programming Manual
Rev 2.1.0
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applications such as spectral monitoring, broadband spectral analysis, and others where the spectral
environment cannot be controlled.
The SC5305A exhibits very low phase noise of -107 dBc/Hz at 10 kHz offset on a 1 GHz RF carrier with a
typical noise floor of -150 dBm/Hz. The noise floor can be further reduced below -165 dBm/Hz by
enabling the internal preamplifier. With gain control between -60 dB to +50 dB, a measurement signal-
to-noise dynamic range greater than 180 dB is achievable. Using high reverse isolation devices and sharp
cutoff filters, LO leakages and other spurious contents at the input connectors are well below -120 dBm.
Inter-stage LO leakages are also kept very low through sophisticated circuit and shielding design to
ensure that spurious in-band signals remain less than -80 dBc. The excellent spurious free dynamic range
is achieved using low noise linear amplifiers, low loss mixers, and high performance solid state
attenuators. State-of-the-art solid state attenuators have improved linearity over earlier designs. Their
attenuation level changes settle under a microsecond, and for applications that involve frequent range
changing, they offer a vastly superior lifetime over mechanical attenuators.
The real-time bandwidth is shaped primarily by the final 70 MHz IF surface acoustic wave (SAW) filter.
The final IF filter has two programmatically selectable paths, switching either between two filter paths
with different bandwidths or between one filter and one bypass (no filter) path. Filters in the first and
second IF stages are not as selective as the final IF filter but they ensure good isolation between local
oscillators (LO). Keeping each LO isolated helps to suppress unwanted spurious signals.
Frequency accuracy is provided by an onboard 10 MHz temperature compensated crystal oscillator
(TCXO) which can be phase-locked to an external reference source if required, and it is recommended to
do so in applications that may require a more stable and accurate base reference.
Signal Path Description
Figure 3 depicts an overall block diagram of the SC5305A. Starting from the upper left, the RF input of
the SC5305A is AC coupled, followed by an elliptic low-pass filter which has a sharp cut-off frequency
slope to ensure the images and unwanted frequencies are well suppressed. Next, a bypass switch
enables or disables the internal preamplifier in the path of the RF signal, directly after the input filter.
The advantage of placing the amplifier before the attenuators is to increase the downconverter
sensitivity when the preamplifier is selected. This switch is programmatically controlled and can be
toggled as required, enabling the preamplifier to boost input signals of very small amplitude. Due to
losses in the attenuators, the noise figure of the system is proportional to their accumulated losses if the
attenuators were placed before the amplifier. The trade-off for better sensitivity is the lack of
attenuation adjustment for larger signals when the amplifier is enabled. The user will need to provide
good judgment when enabling the preamplifier.