Prerequisites - part 1 Digital fundamentals

Let's dive into the prerequisites for ASIC design.

We will discuss Digital Electronics Fundamentals (Combinational gates, Sequential circuits), Verilog Fundamentals, RC Circuits and CMOS fundamentals (operation, characteristics and Fabrication process).

Digital Electronics Fundamentals:

Digital Signal:

Binary system: a number system that has only two possible values for each digit: 0 and 1

decimal	binary	Bit
0	0	1 bit
1	1
2	10	2 bit
3	11
4	100	3 bit
5	101
6	110
7	111
8	1000	4 bit

 

And so on

Combinational Gates: 

• Output depends only on the present inputs.
• Speed is fast
• Easily designed.
• No feedback between input and output
• Time independent
• Elementary building blocks (AND, OR, NAND, NOR, XOR, XNOR MUX etc.)
• NAND and NOR are universal gates.
• Used for both arithmetic and boolean operations.

Applications

• ALU (comparators, programmable logic devices, adder and subtractor)
• Data transmission Circuits (Parallel to serial converters, Data routing, Serial to Parallel converters, Bit compression, ADC & DAC, Encoder and Decoder)
• Code converter circuits

Advantages:

• simplicity
• no delay
• predictable and repeatable results

Disadvantages:

• limited functionality
• less flexibility
• complexity in large designs

Sequential Gates:

• Output depends on both present input and previous output.
• This includes memory elements with combinational circuits
• The memory elements are capable of storing binary information. (Latches and flipflops)

Applications:

• Shift Registers,
• Flip Flop
• ADC and DAC
• Counters     
• Clocks
• Registers inside microprocessors and controllers to store temporary information.
• applied in programmable devices like CPLD, PLD and FPGA

Advantages:

• Memory: store and process data in a specific order (timer and counters)
• Error detection: detects errors in data or instructions, thereby improving reliability.
• Timing: implement timing and synchronization for real-time control.

Disadvantages:

• complex and require more effort to implement.
• consume more power than combinational circuits.
• challenging due to the need to ensure that the timings of the input and outputs are correct.