20110823

Tests conducted on the ADRF6850 with ADC

Test setup:

• R&S 100 - 1000 MHz signal generator
• R&S FSH3 3 GHz spectrum analyser
• ADRF6850 evaluation board
• PIC microcontroller used as SPI configuration programmer
• Centre-tapped transformer converts differential output to single ended for FSH3
• Differential signal AC coupled to THS4521 differential amplifier, then LTC2172-14.
• ADC data is CIC filtered and rate reduced to 10 MHz, FFT, transmitted over Ethernet, then plotted.
• LO set to 140 MHz, gain 40 dB
• Gain of THS4521 is somewhere between 10-20 dB.
• RF test signal at 142.5 MHz

adrf-adc-noinput. Some spurs are visible in the noise.

adrf-adc-142m5-m105. 142.5 MHz at -105 dBm. Signal is just visible at 2.5 MHz.

adrf-adc-142m5-m100. At -100 dBm.

adrf-adc-142m5-m100. At -95 dBm.

adrf-adc-142m5-m100. At -90 dBm.

adrf-adc-142m5-m100. At -85 dBm.

adrf-adc-142m5-m100. At -80 dBm.

adrf-adc-142m5-m100. At -75 dBm.

I also did some quick tests of the dynamic range of the input by examining clipping of one channel of the input and output signal on the THS4521 op amp.

• Input: clips when signal generator is at -39 dBm (with +40 dB gain = 1 dBm)
• Output: clips at -61 dBm (with +55 dB gain = -6 dBm)

I need to have a look at the raw ADC data to see if the ADC's full range is being used.. but I strongly suspect that it is, because the op amp's output is nearly going rail to rail with the -61 dBm input.