Part Number: ADC32RF45EVM
Other Parts Discussed in Thread: ADC32RF45
Description:
I have captured a frequency-dependent increase in the second order harmonic spur (HD2) created by the input signal to the ADC. Even while keeping the input power constant, HD2 dramatically changes as frequency is swept. I would like an explanation from TI regarding this spur and if it is the expected operation of the device.
Hardware setup:
- System setup from EVM Quick Startup Guide was followed closely
- ADC32RF45 placed in Bypass LMFS82820 Mode
- ADC Sampling frequency = 2949.12 MHz
- 2nd Nyquist Zone operation
- ADC Fs signal creation: sig-gen à BP Filter à Splitter à LMK Ref & ADC Clock
- Input signal creation: sig-gen à BP Filter à Splitter à Spectrum Analyzer & ADC Input Ch. A
- EVM Configuration Files: “LMK_ ADC32RF45_LMF_82820_ExtClock.cfg” and “ADC32RF4x_12bit_LMFS_82820.cfg”
Test:
To illustrate what I am seeing, I recorded the HD2 power level as it was reported by the HSDC tool. Five separate input frequencies (1712 MHz, 1975 MHz, 2328 MHz, 2476 MHz, and 2740 MHz) were chosen such that the entire instantaneous bandwidth of the ADC was covered while ensuring that none of the main spurs (interleaving or nth order) overlapped. At each frequency, the signal generator power was altered to ensure that the HSDC Fundamental power was constant at -20 dBFs. This power level was selected to keep the second harmonic generated by the spectrum analyzer hidden in the noise while still able to illustrate the second harmonic created by the ADC. In the plot, the X-axis represents the input signal frequency while the Y-axis shows the power level of the second harmonic. There is a 23.58 dB increase in HD2 over the frequency range while keeping the input power exactly the same.
