This information is part of the Modelica Standard Library maintained by the Modelica Association.

This Four Bit Binary Adder model is one of the five benchmark circuits described in the SPICE3 Version e3 User's Manual (see information of package Spice3).

The model adds two 4-bit numbers (Number A and Number B). It has eight inputs where the first one is the lowest-order bit of the first number (Number A Bit0), the second is the lowest-order bit of the second number (Number B Bit0), the third one is the second-order bit of the first number (Number A Bit1) and so on. The Four Bit Binary Adder has four outputs where the first one (Sum Bit0) is the lowest-order bit, the second and the third one (Sum Bit1 and Sum Bit2) are the next two bits and the last one (Sum Bit3) is the highest-order bit. The picture illustrates the pin-assignment.

Inside the model the names of the inputs refer to the names in the picture as follows:

X1_p1_v --> Number A Bit0

X1_p2_v --> Number B Bit0

X1_p3_v --> Number A Bit1

X1_p4_v --> Number B Bit1

X1_p5_v --> Number A Bit2

X1_p6_v --> Number B Bit2

X1_p7_v --> Number A Bit3

X1_p8_v --> Number B Bit3

X1_p9_v --> Sum Bit0

X1_p10_v --> Sum Bit1

X1_p11_v --> Sum Bit2

X1_p12_v --> Sum Bit3

X1_p14_v --> Cout

The Four Bit Binary Adder is built out of two two bit adders which respectively are built out of two one bit adders. One one bit adder is build out of nine NAND circuits.

Please note, that the simulation time of the Four Bit Binary Adder can take several hours due to its immense size (e.g. 11387 equations).

The user is recommended to simulate from t=0 to t=1e-6s and observe the eight inputs (X1_p1_v, ..., X1_p8_v) and the four outputs (X1_p9_v, ..., X1_p12_v) and the carryout output (X1_p14_v).

The timing of the single transistors of the adder causes a delay which makes it hard to recognize the adder behaviour. Since the Four Bit Binary Adder is a SPICE3 benchmark, the circuit is not changed in order to see the adder behaviour in a better way.

Original SPICE3 netlist of the Four Bit Binary Adder:

ADDER - 4 BIT ALL-NAND-GATE BINARY ADDER

*** SUBCIRCUIT DEFINITIONS
.SUBCKT NAND 1 2 3 4
*   NODES:  INPUT(2), OUTPUT, VCC
Q1        9  5  1 QMOD
D1CLAMP   0  1    DMOD
Q2        9  5  2 QMOD
D2CLAMP   0  2    DMOD
RB        4  5    4K
R1        4  6    1.6K
Q3        6  9  8 QMOD
R2        8  0    1K
RC        4  7    130
Q4        7  6 10 QMOD
DVBEDROP 10  3    DMOD
Q5        3  8  0 QMOD
.ENDS NAND

.SUBCKT ONEBIT 1 2 3 4 5 6
*   NODES:  INPUT(2), CARRY-IN, OUTPUT, CARRY-OUT, VCC
X1   1  2  7  6   NAND
X2   1  7  8  6   NAND
X3   2  7  9  6   NAND
X4   8  9 10  6   NAND
X5   3 10 11  6   NAND
X6   3 11 12  6   NAND
X7  10 11 13  6   NAND
X8  12 13  4  6   NAND
X9  11  7  5  6   NAND
.ENDS ONEBIT

.SUBCKT TWOBIT 1 2 3 4 5 6 7 8 9
*   NODES:  INPUT - BIT0(2) / BIT1(2), OUTPUT - BIT0 / BIT1,
*           CARRY-IN, CARRY-OUT, VCC
X1   1  2  7  5 10  9   ONEBIT
X2   3  4 10  6  8  9   ONEBIT
.ENDS TWOBIT

.SUBCKT FOURBIT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
*   NODES:  INPUT - BIT0(2) / BIT1(2) / BIT2(2) / BIT3(2),
*           OUTPUT - BIT0 / BIT1 / BIT2 / BIT3, CARRY-IN, CARRY-OUT, VCC
X1   1  2  3  4  9 10 13 16 15   TWOBIT
X2   5  6  7  8 11 12 16 14 15   TWOBIT
.ENDS FOURBIT

*** DEFINE NOMINAL CIRCUIT
.MODEL DMOD D
.MODEL QMOD NPN(BF=75 RB=100 CJE=1PF CJC=3PF)
VCC   99  0   DC 5V
VIN1A  1  0   PULSE(0 3 0 10NS 10NS   10NS   50NS)
VIN1B  2  0   PULSE(0 3 0 10NS 10NS   20NS  100NS)
VIN2A  3  0   PULSE(0 3 0 10NS 10NS   40NS  200NS)
VIN2B  4  0   PULSE(0 3 0 10NS 10NS   80NS  400NS)
VIN3A  5  0   PULSE(0 3 0 10NS 10NS  160NS  800NS)
VIN3B  6  0   PULSE(0 3 0 10NS 10NS  320NS 1600NS)
VIN4A  7  0   PULSE(0 3 0 10NS 10NS  640NS 3200NS)
VIN4B  8  0   PULSE(0 3 0 10NS 10NS 1280NS 6400NS)
X1     1  2  3  4  5  6  7  8  9 10 11 12  0 13 99 FOURBIT
RBIT0  9  0   1K
RBIT1 10  0   1K
RBIT2 11  0   1K
RBIT3 12  0   1K
RCOUT 13  0   1K

*** (FOR THOSE WITH MONEY (AND MEMORY) TO BURN)
.TRAN 1NS 6400NS UIC

.control
run
set options no break

*plot v(1) v(2)
*plot v(3) v(4)
*plot v(5) v(6)
*plot v(7) v(8)
*plot v(9) v(10)
*plot v(11) v(12)
*plot v(13)
*print v(9) v(10)
print v(11) v(12) v(13)

.endc

.END

The model is built out of several subcircuits which were described only ones and used several times.

DMOD	Value: Type: ModelcardDIODE Description: Modelcard for diodes
QMOD	Value: Type: ModelcardBJT Description: Modelcard for transistors

X1_p9_v	Default Value: X1.p9.v Type: Real
X1_p10_v	Default Value: X1.p10.v Type: Real
X1_p11_v	Default Value: X1.p11.v Type: Real
X1_p12_v	Default Value: X1.p12.v Type: Real
X1_p14_v	Default Value: X1.p14.v Type: Real
X1_p1_v	Default Value: X1.p1.v Type: Real
X1_p2_v	Default Value: X1.p2.v Type: Real
X1_p3_v	Default Value: X1.p3.v Type: Real
X1_p4_v	Default Value: X1.p4.v Type: Real
X1_p5_v	Default Value: X1.p5.v Type: Real
X1_p6_v	Default Value: X1.p6.v Type: Real
X1_p7_v	Default Value: X1.p7.v Type: Real
X1_p8_v	Default Value: X1.p8.v Type: Real