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AD7980 to BASYS 3 FPGA connection

I am trying to connect EVAL-AD7980-PMDZ to BASYS 3 FPGA using SPI. 

I have a few questions on the connection and interfacing between them.

1.Will the EVAL-AD7980-PMDZ work with 3.3Volts(connected to Pin 6 VCC of Ad7980) from basys 3?(Not using the precision amplifiers).   It is mentioned that in order to enable precision amplifiers to provide zero and full scale inputs to the ADC, -2.5V and 7.5V power needs to be connected. I am confused if this power supply is necessary or if it will work with 3.3V from Basys 2.What is the role of precision amplifiers ? By what factor is the input signal amplified?

3.With the conversion time 1000ns and throughput rate 1MSPS , will the AD7980 sample a input signal with freq of <= 500KHz (going by Nyquist rule). 

Please help me understand them.

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  • Hi Archana96in,

            The EVAL-AD7980-PMDZ requires a 9V wall wart to power up all the circuit in the board, including the LDOs, Reference voltage and amplifiers. This is to plug and play the eval board and use it directly, I am not familiar with the BASYS 3 but as you mentioned it has 3.3V. But please take note that the Vdd of the AD7980 as describe in the datasheet is 2.5V (max 2.625). The amplifiers are drivers to the ADC. This is to ensure correct voltage range are goin in to the ADC from the amplifier and aside from that, the combination of amplifier and ADC makes the system at a high performance. There are many articles that explains why it needs to drive the ADC.

             The conversion time of the AD7980 is maximum at 710ns, 1000ns is the cycle time, combination of conversion and acquisition time. The AD7980 can sample signal <=500khz but the performance is not guaranteed at this signals. A good picture of how would the performance be at frequencies, you can check Figure 18 and figure 21 of the datasheet, SINAD and THD respectively. The performance degrades at increasing frequencies. The performance are guaranteed to have an SNR of 91.5dB at 10Khz at Vref = 5V.

    Regards,

    Jonathan

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  • Hi Archana96in,

            The EVAL-AD7980-PMDZ requires a 9V wall wart to power up all the circuit in the board, including the LDOs, Reference voltage and amplifiers. This is to plug and play the eval board and use it directly, I am not familiar with the BASYS 3 but as you mentioned it has 3.3V. But please take note that the Vdd of the AD7980 as describe in the datasheet is 2.5V (max 2.625). The amplifiers are drivers to the ADC. This is to ensure correct voltage range are goin in to the ADC from the amplifier and aside from that, the combination of amplifier and ADC makes the system at a high performance. There are many articles that explains why it needs to drive the ADC.

             The conversion time of the AD7980 is maximum at 710ns, 1000ns is the cycle time, combination of conversion and acquisition time. The AD7980 can sample signal <=500khz but the performance is not guaranteed at this signals. A good picture of how would the performance be at frequencies, you can check Figure 18 and figure 21 of the datasheet, SINAD and THD respectively. The performance degrades at increasing frequencies. The performance are guaranteed to have an SNR of 91.5dB at 10Khz at Vref = 5V.

    Regards,

    Jonathan

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