Question
ID: 6KXX5142SRNumber: 4E16JU03970Generic: ADRF6516Engineer: Christopher MurphyStatus: Ready to PublishTitle: Min/Max GainVersion: 01Comments: 10/24/2016 - Christopher Murphy - FAQ created.History:StatusFlag: 0Latest: YAText: Analog gain range is always 50 dB no matter what you set the amplifier individual gains. What you have is two VGAs that are cascading after the filter, each having 25 dB of gain range. The preamp can be set to 3 dB or 6 dB gain. Each VGA max gain can be set to 11 dB or 14 dB. And finally, the ADC driver (or post amplifier), can be set to 6 dB or 12 dB of gain. The gains are set via the SPI (see Table 4), but the analog gain range is controlled via the GAIN pin, which has a slope of +15.5 mV/dB. So if you increase the voltage by 15.5 mV on the GAIN pin, the gain will go up by 1 dB. So to answer your questions: - Absolute max gain is +45 dB, which is achieved with the preamp to set 6 dB, the 2 VGAs set to 14 dB (28 dB total), and the post amp set to 12 dB AND with the GAIN pin voltage at 1V (i.e no attenuation in the VGAs). Min gain with these amp settings is -5 dB. - Absolute min gain is -20 dB, which is achieved with the preamp to set 3 dB, the 2 VGAs set to 11 dB (22 dB total), and the post amp set to 6 dB AND with the GAIN pin voltage at 0V. (i.e. max attenuation in the VGAs). Max gain with these amp gain settings is +30 dB. Keep in mind the amps’ gain are design targets. In real life we get a dB less due to insertion loss of the attenuators and other non-idealities.Attachments:$UpdatedBy: CN=Christopher Murphy/OU=Europe Support/O=ADI World
1) What is the maximum gain of this part ? I think +45dB , could you plsconfirm.
2) What is the minimum gain of this part ? I think -5dB, could you plsconfirm.
Answer
Analog gain range is always 50 dB no matter what you set the amplifierindividual gains. What you have is two VGAs that are cascading after thefilter, each having 25 dB of gain range. The preamp can be set to 3 dB or 6 dBgain. Each VGA max gain can be set to 11 dB or 14 dB. And finally, the ADCdriver (or post amplifier), can be set to 6 dB or 12 dB of gain. The gains areset via the SPI (see Table 4), but the analog gain range is controlled via theGAIN pin, which has a slope of +15.5 mV/dB. So if you increase the voltage by15.5 mV on the GAIN pin, the gain will go up by 1 dB.
So to answer your questions:
- Absolute max gain is +45 dB, which is achieved with the preamp to set 6 dB,the 2 VGAs set to 14 dB (28 dB total), and the post amp set to 12 dB AND withthe GAIN pin voltage at 1V (i.e no attenuation in the VGAs). Min gain withthese amp settings is -5 dB.- Absolute min gain is -20 dB, which is achieved with the preamp to set 3 dB,the 2 VGAs set to 11 dB (22 dB total), and the post amp set to 6 dB AND withthe GAIN pin voltage at 0V. (i.e. max attenuation in the VGAs). Max gain withthese amp gain settings is +30 dB.Keep in mind the amps’ gain are design targets. In real life we get a dB lessdue to insertion loss of the attenuators and other non-idealities.