Modular gray code counter
A Gray code counter has multiple two-bit Gray code counter modules, clock gated integrated cells (CGICs), and a parity bit generator. The CGICs gate clock signals provided to the two-bit counter modules, which reduces dynamic power consumption. The parity bit generator generates a parity bit that indicates a count of binary ones in a counting state.
1. A Gray code counter stage of an n-bit Gray code counter circuit, comprising:
a first OR gate for receiving (n-4)th and (n-5)th Gray code bits and generating a first intermediate signal at an output terminal thereof;
a first AND gate connected to the output terminal of the first OR gate for receiving the first intermediate signal and a first enable signal, wherein the first AND gate generates a second enable signal at an output terminal thereof, wherein the first enable signal is generated based on a parity bit and a zeroth Gray code bit;
a first CGIC connected to the output terminal of the first AND gate for receiving the second enable signal and a clock signal and generating a first gated clock signal;
a first counter circuit connected to the first CGIC for receiving the first gated clock signal and a first direction bit and generating a (n-4)th Gray code bit and the (n-3)th Gray code bit;
a second CGIC for receiving a third enable signal and the clock signal and generating a second gated clock signal;
a first flip-flop having an input terminal for receiving an inverted first direction bit, a clock input terminal connected to the second CGIC for receiving the second gated clock signal, and an output terminal connected to the first counter circuit, wherein the first flip-flop generates the first direction bit at the output terminal thereof;
a first NOT gate connected to the output terminal of the first flip-flop for receiving the first direction bit, and connected to the input terminal of the first flip-flop, wherein the first NOT gate generates the inverted first direction bit;
a NOR gate for receiving the zeroth Gray code bit, and first through (n-4)th Gray code bits and generating a second intermediate signal at an output terminal thereof;
a second AND gate connected to the output terminal of the NOR gate for receiving the second intermediate signal and the parity bit, wherein the second AND gate generates the third enable signal at an output terminal thereof, wherein the output terminal is connected to the second CGIC for providing the third enable signal;
a third CGIC connected to the output terminal of the second AND gate for receiving the third enable signal and the clock signal and generating a third gated clock signal; and
a second counter circuit for receiving a second direction bit and the third gated clock signal and generating (n-1)th and (n-2)th Gray code bits.
2. The Gray code counter stage of claim 1 , wherein the first counter circuit comprises:
a XOR gate for receiving the first direction bit and the (n-4)th Gray code bit and generating a third intermediate signal at an output terminal thereof;
a second flip-flop having an input terminal connected to the output terminal of the XOR gate for receiving the third intermediate signal, and a clock input terminal connected to the first CGIC for receiving the first gated clock signal, wherein the second flip-flop generates the (n-3)rd Gray code bit at an output terminal thereof;
a XNOR gate for receiving the first direction bit and the (n-3)rd Gray code bit and generating a fourth intermediate signal at an output terminal thereof;
a third AND gate for receiving inverted (n-4)th and (n-3)rd Gray code bits and generating a fifth intermediate signal at an output terminal thereof;
a second OR gate connected to the output terminal of the XNOR gate for receiving the fourth intermediate signal and to the third AND gate for receiving the fifth intermediate signal and generating a sixth intermediate signal at an output terminal thereof; and
a third flip-flop having an input terminal connected to the output terminal of the second OR gate for receiving the sixth intermediate signal, and a clock input terminal connected to the first CGIC for receiving the first gated clock signal, wherein the third flip-flop generates the (n-4)th Gray code bit at an output terminal thereof.
3. The Gray code counter stage of claim 2 , wherein n is an even positive integer.