Question about ADRF6518

Hello everyone, what is the maximum gain that adrf6518 can achieve? whether the digital gain  is up to 66 db, but the vgn1/2/3 voltage versus gain curve maximum gain is about -8 db. such that the total gain is maximum for 66-24=42 db. But the maximum gain in figure 2 can be 66 db, and I want to know what this is all about(Figure 1 is a screenshot of the filter mode and Figure 2 is a screenshot of the bypass mode).I want to know how much the maximum gain of the filter mode can be? what is vgn1/2/3 at this time? 

  • +1
    •  Analog Employees 
    on Jan 7, 2020 4:22 PM

    The simple answer is that the maximum possible gain is +66 dB.

    The ADRF6518 has 3 variable gain amplifiers (VGA), each of which have an analog gain range of 24 dB which are controlled via the VGN1, VGN2 and VGN3 pins (shown in Figures 5, 6 and 7; also these figures should state that the VGNx voltages not swept are set to 0V and the digital gain code = 0b1111110, which is the lowest possible max gain settings).  Each of these VGAs can change their maximum gain via the digital SPI port.  Additionally, the last gain block (ADC driver) can change its gain from either 3 dB or 9 dB; this is controlled via SPI.  This is outlined in Figure 68 pasted below.

    This allows for 72 dB of analog gain range (each VGA has a 24 dB attenuator) which can move up to 30 dB depending on the maximum gain settings.  For example, if the max gains of the VGA1/2/3 are set to 15/21/21 dB and the ADC driver is set to 9 dB, the resultant possible gain range is from +66 dB (VGN1/2/3 = 1V) down to -6 dB (VGN1/2/3 = 0V).  But if you set VGA1/2/3 to 9/12/12 dB and the ADC driver to 3 dB, the resultant gain range is +36 to -36 dB.  

    The gain difference between filter mode and bypass mode is small, maybe 1 dB.