# theoretical queries regarding circuits

Status
Not open for further replies.

#### sonika jha

##### New Member
is there any difference between the design of analog and digital circuits I mean in terms of connections and components?thnku...

#### cowboybob

##### Well-Known Member
Well, yes.

Could you be more specific?

#### sonika jha

##### New Member
Well I happened upon a statement portraying the difference-"digital circuits comprises of digital components and analog circuits comprises of analog components" ,but digital circuits comprises of transistors which is also used in analog circuits.So I cant seem to find the difference as far as components are concerned.

Moreover is there any difference in the mode of connections being made between the components in the two cases (like wires in one and not in other)?thnku...

#### chemelec

##### Well-Known Member
Yes Digital Components are made up using Analogue components (Transistor, resistors, capacitors & ETC)
But the FUNCTION of Digital Circuits is Different than that of Analogue Circuits.

#### sonika jha

##### New Member
sir if I understood correctly digital components (ICs,multiplexers,etc) comprises of digital circuits containing analog components.thnku...

#### cowboybob

##### Well-Known Member
sir if I understood correctly digital components (ICs,multiplexers,etc) comprises of digital circuits containing analog components.thnku...
That is correct.

Your definition of "circuit" needs expansion: there are circuits within ICs and the are circuits made up of ICs.

The circuit(s) one would find in a digital IC are, indeed, generally made up of analog devices, as you state. BUT the IC functions are digital, i.e., signals produced are, for the most part, simply "On" or "Off" - the basic definition of "digital".

Analog circuits, however, have outputs that can "range" or vary across values (often 0 volts to some higher (or lower) value voltage and everything in between.

Moreover is there any difference in the mode of connections being made between the components in the two cases (like wires in one and not in other)?thnku...
The connections, in both, are pretty much exactly the same. Frequency levels (low vs. high) and power considerations make a difference in placement, density and length, but otherwise there are no significant differences.

#### Tony Stewart

##### Well-Known Member
ADvanced Logic design assumes you know all the fundamentals of Analog design of Noise Immunity, EMI, transmission theory for high speed reflections and prop delay, signal threshold, switching rise times, setup,time, effects of controlled impedances on tracks/gnd plane, differential + common mode impedance on line driver/receivers , transient current supply decoupling, ESR, ESL , race conditions, etc., current mode high speed logic, etc

NEw Logic designers must learn the above, while learning the tools for SSI, MSI, LSI, VLSI, VHDL, CPLD, uC machine language with higher levels of design tools and chipsets.

EVentually all logic design is based on **Analog principles** with logical use of libraries using AND OR gates and Memory Flip Flops in small scale(SSI) up to billions of devices per CPU.

The assumed properties above bipolar or CMOS switches running at the transition slew rate are critical in the layout compatibility for EMC and interfacing to sensors and power driver's.

RF and Power design is another world of Analog Design.

But like learning chess , you start slow and quickly accelerate to learn all the circuits that exist, so you don't have to reinvent the wheel, then choose the best to suit a custom application in make or buy decisions. Sometimes you invent a new method, but it probably has been done before somewhere else in the universe.

Status
Not open for further replies.