# How does the ADRF6516's gain adjust via the Gain Control Pin (i.e. Vgain)?

Document created by analog-archivist on Feb 23, 2016
Version 1Show Document

### Q

How does the ADRF6516's gain adjust via the Gain Control Pin (i.e. Vgain)?

### A

The gain pin does control the attenuation in the signal chain and Figures like
Figure 47 show the Gain + Attenuation.  The whole signal chain produces a slope
of 15 mV/dB.

The total gain will depend on the gain of the gain blocks AND the attenuation.
Also, the gains of the gain blocks can vary (this is controlled via the SPI
port and is referred to as digital gain in the datasheet (refer to Table 4).

So, if you have Vgain = 0V you can either have:

Gain (dB) = [Gain of gain blocks] - Attenuation

Gain (dB) = [3 + 11 +11 + 6] – 50 = -19           Gain code [B3:B1] = 000
Gain (dB) = [3 + 14 +14 + 6] – 50 = -13           Gain code [B3:B1] = 001
Gain (dB) = [3 + 11 +11 + 12] – 50 = -13          Gain code [B3:B1] = 010
Gain (dB) = [3 + 14 +14 + 12] – 50 = -7           Gain code [B3:B1] = 011
Gain (dB) = [6 + 11 +11 + 6] – 50 = -16           Gain code [B3:B1] = 100
Gain (dB) = [6 + 14 +14 + 6] – 50 = -10           Gain code [B3:B1] = 101
Gain (dB) = [6 + 11 +11 + 12] – 50 = -10          Gain code [B3:B1] = 110
Gain (dB) = [6 + 14+ 14+12] – 50 = -4             Gain code [B3:B1] = 111

So, if you have Vgain = 1V that means there is no attenuation, or 0 dB.  So,
referring to the theoretical equation above, at Vgain = 1V, it would look like:
Gain (dB) = [6 + 14+ 14+12] – 0 = +46dB             Gain code [B3:B1] = 111

Remember, the real-life tolal gain (for Gain code = 111) are not quite -4dB and
+46db and are closer to -5dB and +45dB respectively (refer to Table 1 in
datasheet Rev.B)