
SEC ASIC
6-19
STD80/STDM80
Carry-Select Adder
Features
Two’s complement or unsigned magnitude operation
Functional model, test vector, schematic, and layout generators
Timing model with auto-characterization
Sophisticated double carry-select algorithm
Two’s complement overflow flag
n-bit (4 to 128) Adder
Three drive strength options for output
General Description
The Carry-Select Adder performs two’s complement addition or unsigned magnitude operation. The high
performance Carry-Select Adder design can have layout leaf cells optimized for multiple-targeted
technologies. The overflow flag gets set if an overflow occurs while adding two positive or negative numbers.
The overflow is ignored for unsigned magnitude operations.
Design Description
The Carry-Select Adder performs high speed binary addition by using a sophisticated double carry-select
algorithm with group delay equalization for carry propagation. The outer carry-select scheme is used to
provide a short path between the low order inputs and the high order outputs. The internal carry-select
schemes are placed within these blocks to reduce their block propagation delays. The sizes of the
carry-select blocks increase along the carry propagation tree to produce a fast addition. An n-bit wide operand
(AIN), an n-bit wide operand (BIN), a 1-bit wide input carry signal (CIN), and an n-bit wide output bus (SOUT)
and 1-bit output carry signal (COUT) serve as the I/O signals to the module. The generated layout is
constrained to four rows of cells for minimal area consumption.
This fast Carry-Select Adder is configured for your highest performance applications and outperforms normal
Carry-Select Adders by modulating the size of the groups to equalize carry propagation delay, and by
providing a second level of carry-select scheme.
Symbol
Parameter Description
Parameter Name
instance_name
bits
overflow
Description
Range
Name of Carry-Select Adder instance to be generated
Number of bits in the input data bus
It determines whether overflow output is present;
0: no overflow; 1: overflow
Drive strength
Any string
4 to 128
0/1
drv
1/2/4
AIN [bits–1:0]
SOUT [bits–1:0]
BIN [bits–1:0]
CIN
COUT
OVF (optional)
+/–