adc2:simulations:fft_freq_mismatch
fft freq mismatch
- fsampling = 20 Msps
- fin ~= 3Mhz (2459 peak)
- FFT len 16384
- fbase = 20e6/16384 ~= 1220.703125 Hz
| diff [hz] | % fbase | left [dB] | right [dB] | SINAD [dB] | THD [dB] | SNHR [dB] | SFDR [dB] |
|---|---|---|---|---|---|---|---|
| -207.52 | -17.00 | -13.8 | -16.8 | 10.0 | -68.8 | 10.0 | 13.8 |
| -109.86 | -9.00 | -20.1 | -21.7 | 15.7 | -74.2 | 15.7 | 20.1 |
| -61.04 | -5.00 | -25.6 | -26.4 | 20.8 | -79.3 | 20.8 | 25.6 |
| -36.62 | -3.00 | -30.2 | -30.7 | 25.3 | -83.7 | 25.3 | 30.2 |
| diff [hz] | % fbase | left [dB] | right [dB] | SINAD [dB] | THD [dB] | SNHR [dB] | SFDR [dB] |
|---|---|---|---|---|---|---|---|
| 36.62 | 3.00 | -30.7 | -30.2 | 25.3 | -83.6 | 25.3 | 30.2 |
| 61.04 | 5.00 | -26.4 | -25.6 | 20.8 | -79.1 | 20.8 | 25.6 |
| 109.86 | 9.00 | -21.7 | -20.1 | 15.7 | -74.0 | 15.7 | 20.1 |
| 207.52 | 17.00 | -16.8 | -13.8 | 10.0 | -68.5 | 10.0 | 13.8 |
| diff [hz] | % fbase | left [dB] | right [dB] | SINAD [dB] | THD [dB] | SNHR [dB] | SFDR [dB] |
|---|---|---|---|---|---|---|---|
| -37.84 | -3.10 | -29.9 | -30.4 | 25.0 | -83.4 | 25.0 | 29.9 |
| -20.75 | -1.70 | -35.2 | -35.5 | 30.2 | -88.6 | 30.2 | 35.2 |
| -10.99 | -0.90 | -40.8 | -41.0 | 35.7 | -94.1 | 35.7 | 40.8 |
| -6.10 | -0.50 | -46.0 | -46.1 | 40.8 | -99.2 | 40.8 | 46.0 |
| -3.66 | -0.30 | -50.4 | -50.5 | 45.3 | -103.6 | 45.3 | 50.4 |
| -2.44 | -0.20 | -54.0 | -54.0 | 48.8 | -107.2 | 48.8 | 54.0 |
| -1.22 | -0.10 | -60.0 | -60.0 | 54.8 | -113.2 | 54.8 | 60.0 |
| diff [hz] | % fbase | left [dB] | right [dB] | SINAD [dB] | THD [dB] | SNHR [dB] | SFDR [dB] |
|---|---|---|---|---|---|---|---|
| -3.78 | -0.31 | -50.1 | -50.2 | 45.0 | -103.4 | 45.0 | 50.1 |
| -2.08 | -0.17 | -55.4 | -55.4 | 50.2 | -108.6 | 50.2 | 55.4 |
| -1.22 | -0.10 | -60.0 | -60.0 | 54.8 | -113.2 | 54.8 | 60.0 |
| -0.61 | -0.05 | -66.0 | -66.0 | 60.8 | -119.2 | 60.8 | 66.0 |
| -0.38 | -0.03 | -70.2 | -70.2 | 65.0 | -123.4 | 65.0 | 70.2 |
| -0.21 | -0.02 | -75.4 | -75.4 | 70.2 | -128.6 | 70.2 | 75.4 |
| -0.12 | -0.01 | -80.0 | -80.0 | 74.8 | -133.2 | 74.8 | 80.0 |
| -0.06 | -0.01 | -86.0 | -86.0 | 80.8 | -139.2 | 80.8 | 86.0 |
remark : 1%@20Mhz@16kp = 12.7 Hz
conclusion : if we want to achive resonable measurement resutls for 10-bit ADC working @ 20 Mhz (and with 16k FFT len) input signal freq should not differ from ideal one more then ~1 Hz.
conclusion 2 : reducing lenght of FFT (fbase is becoming larger) should relax this requirement (but also degrade precision of measurement)
/services/www/http/wiki/data/pages/adc2/simulations/fft_freq_mismatch.txt · Last modified: 2019/03/08 14:08 (external edit)
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