Dear ‘not-a-moderator ’, MK28,
Thanks for the response
Fast transient response parameters for LDO – already checked and TPS75801 meets these requirements
GSM module is controlled by uP. uP communicate with GSM module through UART and through AT commands, I checked all the parameters like signal strength, GPRS connection, GSM UART parameter settings, SIM card details, GSM module FW/HW versions, etc. Everything is fine. Signal quality is around ~ -58dBm to -60dBm
SIM is not a locked SIM.
One more observation:
Board is booted up without GSM antenna. Voice Call can be made to the GSM number. But signal quality is poor comparatively ( -72dBm to -78dBm). If I connect antenna, signal quality is around -54dBm to -51dBm. (Maximum value given by U-blox).
In brief, Presence of antenna during power-on of GSM is affecting somehow the whole board and uP freezes.
After this observation, I tried few values and zeroed on 5.1nH@L103,
3pF@C114.These value provides signal quality of ~ -60dBm. So far (18hours), it works fine for all the SIM cards.
There is no details regarding GSM ANT pin impedance in the datasheet. I was using the filter circuit from their reference design but different antenna.
My concern is Is this called ‘mismatch’ between antenna and filter circuit? Though these values works fine for now, i want to understand the reasons for the issue.
I want to understand how to arrive these values through design calculation. can you please help me on these?I am novice on RF design.
best regards
Ramesh