Patent EP-0080970-A1 (EP)
Inventor: ELMIS HERBERT ING GRAD
IPC: H03K23/66
Filed: 1982-03-30
Abstract: 1. Frequency divider presettable to fractional divisors (c/e) which includes a counter (Z) presettable to integers, and wherein - those stages (Rb) of a divisor register (R) which hold the fractional parts (b) of the divisor (c/e) in decimal point representation (a + 0.b) are connected to the first input (E1) of a first adder (A1) having its output (A) coupled to the input of a buffer memory (S), - the output of the buffer memory (S) is coupled to the second input (E2) of the first adder (A1) and to the set input (Es) of a digitally adjustable delay line (V) whose setting-step width is equal to the period (T) of the divider's input signal (F) divided by the denominator (e) of the divisor (c/e), and whose input is connected to the maximum-count output (Am) of the counter (Z), and - the overflow output (Ao) of the first adder (A1) is coupled to the least-significant-digit terminal (LB) of the first input (E1) of a second adder (A2), whose second input (E2) is connected to those stages (Ra) of the divisor register (R) holding the integral parts (a) of the divisor (c/e), and whose output (A) is coupled to an input of the counter (Z), characterized by the following features : - the enable input (En) of the buffer memory (S) is connected to one of the count outputs (An) of the counter (Z) which lie before the maximum-count output (Am) ; - the output (A) of the second adder (A2) is connected to the set input (Es) of the counter (Z) ; - the frequency divider is implemented using insulated-gate field-effect transistor technology (MOS technology) ; - for each digit of the fractional parts (b) of the divisor (c/e), the first adder (A1) and the buffer memory (S) are combined in cells of a first kind (z1) and cells of a second kind (z2) which succeed each other by turns ; - the cell (z1) of the first kind is a ripple-carry adder stage comprising a first complex logic-circuit block (1j), a second complex logic-circuit block (2j), two inverters (i1, i2), and three transistors (t1, t2, t3), with - the controlled current paths of the first and second transistors (t1, t2) connected in series between the output of the first complex logic-circuit block (1i) and the output of the first inverter (i1), which has its input connected to the output of the second inverter (i2), - the input of the second inverter (i2) connected to the node of the controlled current paths of the first and second transistors (t1, t2), ad the output of the second inverter (i2) connected via the controlled current path of the third transistor (t3) to the second input (E2) of the ripple-carry adder stage, whose first input is the first input (E1) of the first adder (A1), - the gate of the first transistor (t1) being the enable input (En) of the buffer memory (S), and the gate of the second transistor (t2) connected to this enable input (En) via a third inverter (i3), which is common to all cells (z1, z2) of the first kind and the second kind, and - the output of the second inverter (i2) being the output of the cell (z1) of the first kind ; - the cell (z2) of the second kind consists of the same subcircuits as the cell (z1) of the first kind which are interconnected in the same manner, but the output of the first inverter (i1) is the output of the cell (z2) of the second kind, and the first input of this cell (z2) is preceded by a fourth inverter (i4), - the second adder (A2) consists of stages of a first kind (s1) and of stages of a second kind (s2) which succeed each other by turns, - the stage (s1) of the first kind consists of a two-input NOR block (5), a fifth inverter (i5), and a third complex logic-circuit block (3), with - the second input (E2) of the first adder (A1) being the input of the fifth inverter (i5), - the third complex logic-circuit block (3) containing a two-input AND gate (31) whose output is NORed with the carry output (Cl), - the carry input (Ck) connected to the first input of the NOR block (5) and to the first input of the AND gate (31), whose second input, together with the second input of the NOR block (5), is connected to the output of the fifth inverter (i5), and - the output of the third complex logic-circuit block (3) being the output (A) of the stage (s1) of the first kind, and the output of the NOR block (5) being the carry output (Cl) of this stage (s1), and - the stage (s2) of the second kind consisting of a two-input NAND block (6), a fourth complex logic-circuit block (4), and a sixth inverter (i6), whith - the fourth complex logic-circuit block (4) containing a two-input OR gate (41) whose output is NANDed with the carry output (Cl), - the carry input (Ck) connected to the first input of the NAND block (6) and to the first input of the NOR gate (41), whose second input, together with the second input of the NAND block (6), is the input of the stage (s2) of the second kind, and - the output of the NAND block (6) being the carry output (Cl) of the stage (S2) of the second kind, and the output of the sixth inverter (i6) being the output (A) of this stage (s2).