Dear All,
Would you please give me an idea about what's digital ground and analog ground short/common at one place only? Does the supply power ground to both analog and digital ground count one?
Here it's the detail:
Recently I'm using a C2000(28027) to develop a meter.
The digital part include TMS320F28027,RS232;The analog part include transformer,switch(CD74HC4052),amplifer(OP27),programable amplifer(PGA112).
The flow chart is:
28027 send GPIO signals to set switch
28027 send 5 pwm pulse to start the transmitter
wait till the transmitter calm
28027 send gpio signals to set pga
start ADC
Calculating by 28027
send out result by RS232
I split the analog ground with the digital ground,generate analog supply from digital supply. The analogy ground connect to the supply power ground, the digital ground also connect to the supply power ground, so the analog ground plane and digital ground plane are connected at the supply power ground, does this connect point count as one comon point? If yes, there should not be any more common point between the analog ground plane and digital ground plane. But if there is no other common point between the analog and digital ground plane, the PGA doesn't work, it's in sleep state, when I add wires to get the digital and analog ground connected, PGA works well and ADC signal is good. But in this way, is it the analog and digital ground connect by two points? Another way to get PGA work is to enlarge the common point between the analog and digital ground, I enlarge the common point to 14mm wide, in this way, PGA works but the ADC signal is poor?
How should I connect the analog and digital ground together? Should I set a 3-5mm wide connect area near the supply power ground and put all the switch and pga control signal nearby the conncet area? or should I connect the analog and digital ground by a second bridge and put switch and pga control signal nearby the second bridge? We need PGA work and also the ADC signal need be good, otherwise the result could fail.
Thanks!
Tyler