Other Parts Discussed in Thread: LMX2541, LMX2594, LMX2581, LMX2571
Question:
I have an RF transceiver operating in Half duplex under TDMA mode, each transmitter and receiver has its own PLL frequency synthesizer, I would like turn off PLL from transmitter during reception cycle and turn it on during transmitting cycle, PLL is on for 10msec and off for 90msec (10% of TDMA duty cycle, one full cycle lasts 100msec). I found that there are three modes to Turn ON/Turn OFF LMX2531 either by firmware or hardware and my concern is that how fast in frequency transient of PLL synthesizer before its output frequency becomes stable within x% of error from steady state:
1- Hardware: Set “CE” line (pin 11 of LMX2351) "HIGH" to turn on and "LOW" to turn off LMX2531
2- Firmware (Set corresponding bit in the register R5 of LMX2531): Set either “EN_PLL” or “EN_VCO” or “EN_VCOLDO” or “EN_PLLLDO1” to turn ON (corresponding bit =1) or turn OFF (corresponding bit =0)
3- Hardware: Apply 0V or 3V to VccVCO pin (pin 16) of LMX2531 to turn off or turn on internal VCO. Please comment if this mode is not recommended.
Question: Among three modes mentioned above, What is a most reliable mode to turn on and turn off PLL LMX2531? What mode should I consider to achieve shortest switching time going from Off state (VCO free running frequency) to steady state of a desired output frequency? Serial programming time (DATA, CLK, LE) to LMX2531 mentioned from 2) is taken into consideration of the comparison.
I’ve used Signal Source Analyzer from Keysight in the pass to measure transient switching time of PLL synthesizer, and my company is not equipped with such an equipment to qualify what is the shortest achievable switching time before output frequency from PLL synthesizer become stable, please advise.
Best regards,
Tien
