Rev 1.1 | SC5317A & SC5318A
Hardware Manual
SignalCore, Inc.
8
SC5317A & SC5318A Hardware Manual
Absolute Gain of the RF Conversion Path
Assuming independency, and to be able to compute the gain of the downconverter at any setting, an
absolute reference state of the device must be determined first. Once this reference state is established,
compensation can be applied to other relative configured states of the device. The established reference
state of the device is as follows:
•
All attenuators are set to 0 dB
•
IF value is set at 1.25 GHz
•
RF preamplifier is disabled.
•
RF is tuned from 6000 MHz to 26500 MHz in 250 MHz steps
The gain of the device in this state is measured at different frequencies in the range of 6000 MHz to
26500 MHz. This set of measurements is the RF absolute gain stored at starting address 0xBD0 of the
calibration EEPROM. All other measurements taken as deviations from this reference setting are relative.
Gain Through the Bypass RF Conversion Path
The absolute gain through the bypass path is stored beginning at address 0x7A8. The absolute gain
measurement is made every 250 MHz, between 6000 MHz and 26500 MHz.
Applying Calibration
The gain and attenuator values are relative measurements from the absolute reference values made over
various RF frequencies. These relative values are either subtracted (attenuation) or added (gain) to the
absolute gain value to determine the gain of the relative configuration. For example, assume the
RF_ATTEN is at 5 dB, IF3_ATTEN is at 2 dB, IF frequency set to 1950 MHz, and the RF frequency is set to
13.1 GHz. A possible systematic approach would be:
1.
Compute the absolute gain value by interpolation because there is no measurement value at 13.1
GHz. A simple linear interpolation between the measured 13.0 GHz and 13.25 GHz values would
provide a good estimate. A local spline interpolation over 5-6 surrounding points would provide
better accuracy. Let’s call this value
𝐺(𝑟𝑓)
.
2.
Compute the relative RF attenuator value by interpolation because there is no measurement
value at 13.1 GHz. A simple linear interpolation between the measured 13.0 GHz and 13.25 GHz
values would provide a good estimate. A local spline interpolation over 5-6 surrounding points
would provide better accuracy. Let’s call this value
𝐴(5𝑑𝐵, 𝑟𝑓)
𝑟𝑓_𝑎𝑡𝑡𝑒𝑛
.
3.
The IF Attenuator value is read directly from memory as
𝐴(2𝑑𝐵)
𝑖𝑓_𝑎𝑡𝑡𝑒𝑛
, however it must be
corrected for frequency offset from 1250 MHz. There are offset gain response values measured
at 1900 MHz and 2000 MHz, so a simple linear interpolation between 2 points should be
sufficient. Call this correct gain value
𝐺(𝑖𝑓)
.
4.
The gain for this configuration is calculated using:
𝐺 = 𝐺(𝑟𝑓)
𝑎𝑏𝑠
+ 𝐺(𝑖𝑓) −
𝐴(5𝑑𝐵, 𝑟𝑓)
𝑟𝑓_𝑎𝑡𝑡𝑒𝑛
− 𝐴(2𝑑𝐵)
𝑖𝑓_𝑎𝑡𝑡𝑒𝑛