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Do I have/need an Analog Ground for this?

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blapcb

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I am designing a telematics unit (i.e. GPS vehicle tracking), and have a doubt about whether or not I have/need an analog ground. Essentially it is a digital board, consisting of a uC (MSP running at 6MHz), RTC, EEPROM, and serial devices connected on UART, some TTL on board and some via level shifters (RS232). The only things "analog" I can think of are:
a) The input signals coming from the outside which are all "logic" signals (on/off) or pulses from like a hall effect
b) There is an RFID module also and the antenna from the module (two connections) are routed form the module via the main PCB to an external connector
Presently there is only one ground on the PCB. But should I have an analog ground? For which parts of the circuit?
Thanks
 

sherazi

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The analog ground on MCUs is for the analog parts of the MCU, you can connect it to the digital ground if you are not using the features!
 

blapcb

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The analog ground on MCUs is for the analog parts of the MCU, you can connect it to the digital ground if you are not using the features!

Of course if you are using a ADC/DAC you need an analog ground, but I don't think that the use/need for analog ground is limited to when you are using it on a MCU. There are other "analog" things other than ADC/DAC right? For example in my design, if the entire RFID circuit was on the main PCB and not on a module, definitely that would constitute as being analog also right? So I think the question is still valid IMHO.
 

raylay

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I think you needn't get an separately analog ground, just keep the sensitive signal with good grounding protect.and RF trace have those needed impedence.
 

ea.arun

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i will prefer to separate the grounds if i have high frequency switching digital/mixed signal circuitries(a fast sampling/output ADC for ex.) which can couple noise into a sensitive analog section......i think in your case you dont have such an issue....also it lot dependent on component placement and curent return path.....
definitely your RFID section requires a solid ground plane for the rf section....separate the section from noisy sections such as switching dc-dc converter.....but can provide the same solid ground plane....
but considering your other sections such as RS232,EEPROM and the digital inputs from hall sensor seems you dont need any separate ground....you can just playaround with your placement a little to separate the sections.......
 

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