Chapter 13
Interfacing Analog and
Digital Circuits
Circuits
Analog Signals
Analog Signals
Signals that vary continuously throughout a
th
th
defined range.
Representative of many physical quantities, such as
of many physical quantities such as
temperatur
Asynch Modulo 8 Up Counte
sy
Up Cou er
This counter counts 000 001 111 000
Assumes output is in order Q2 Q1 Q0
Modulo 8 up counter
The lower order flip-flop is synchronized to the Clock
All other flip-flops are not asynchronous
Also called ripple counter
4 Bit Ring Counter Using a Decode
Cou
Us
ecoder
Counts 1000 0100 0010 0001 1000
Ring Counter Using D Flip-Flops
Cou
Us
A design that uses a minimum of combinational
logic, but uses more flip-flops
asynchronous preset
Q0
Q1
Qn 1
Start
D
Q
Q
Clock
D
Q
Q
D
Sequential Circuit Analysis
The current state at time t is stored in an array of ip- ops.
The next state at time t +1 is a Boolean function of current state
and inputs.
The output is a Boolean function of current state and (sometimes) inputs.
State(t)
Inp
Sequential Systems
No state: Combinational logic system: Output := f (Inputs).
Combinational
circuit
n inputs
m outputs
State present: Sequential logic system: Output := f (Inputs State).
cfw_ Synchronous sequential system: State updated at discrete
time.
Chapter 6
Digital Arithmetic and
Arithmetic and
Arithmetic Circuits
Digital Arithmetic
Signed Binary Number: A binary number of fixed
length whose sign (+/-) is represented by one bit
(usually the MSB) and its magnitude by the
remaining bits.
bit
Unsign
Propagation Delay for an Inverter
High-to-low (tPHL ) and low-to-high (tPLH ) propagation delays are
measured on output transitions.
Rise
time
Fall
time
IN
90%
50%
10%
IN
OUT
OUT
90%
50%
10%
t
t
PHL
PLH
77
Digital Logic Families: Bipolar Transistors
Gates
Simplification of Logic
Simplification of Logic
Circuits
Two methods can be used to
simplify a logic circuit: one uses
Boolean algebra theorems; the
th
th
other uses a mapping technique.
The methods of logic-circuit
simplification that we will study
req
Boolean Algebra
21
Boolean Algebra
Al
Now that we understand the concept of
binary numbers, we will study ways of
describing how systems using binary
describing how systems using binary
logic levels make decisions.
Boolean algebra is a branch of
algebra
VHDL Coding Basics
Overview
Chip
Libraries
Library ieee;
Use ieee.std_logic_1164.all;
Use ieee.std_logic_arith.all;
Use ieee.std_logic_signed.all;
Use ieee.std_logic_unsigned.all;
Data Types
bit values: '0', '1'
boolean values: TRUE, FALSE
integer