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Some basic question about analog circuit.

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Full Member level 3
Jul 22, 2007
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I am a digitial circuit designer. I want to know what's difference between the digitial and analog circuit. And what is the advantage and disadvantage of the analog and digital circuit.
I found the power management chip is usually designed using analog circuit.
Can it be designed using digital circuit?
Last question, as we know PLL is an analog device. It is usually located in the digital IC chip. But why there is no ADC between the PLL output and the rest of the digital circuit?
Thank you!

Hi Owen,

Digital circuit will utilize Mosfet switching while analog circuit uses Mosfet in saturation region (Typically) i.e. in conducting mode. The Id and Vgs relation is essential in analog circuit working.

I dont have any idea about power management cell.

PLL is used to ensure a certain phase relationship is maintained between signals (for eg:- clocks) . So in effect it works on the analog properties of digital signal( eg. clock of digital circuit) and hence dosent require ADC. It will monitor and effect analog properties of signal.
Hope this helps.


Yes digital can be used for switching power supplies, but for now it is not usually cost effective except for the most expensive/complex designs. They do exist now.

Digital circuits are a special case of analog circuits, just a matter of terminology and way how you deal with an electrical signal, that can be considered why power management in IC's is analog part, it is just to monitor the voltage level in terms of voltage and current not 0's and 1's.
PLL inside digital IC's like microcontrollers is a digital input digital output PLL, so no difference between it and the rest of the system and so it doesn't need an ADC.

PLL is used for clock generation in the digital chip,so a ADC is unnecessary. ADC is widely used as the signal interface between the analog circuit and digital circuit.

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