An arithmetic apparatus used for a neural network includes a plurality of digital-time conversion circuits connected in series and a time-digital conversion circuit connected to a last digital-time conversion circuit in the series. Each of the digital-time conversion circuits is configured to delay a first input time signal by a variable amount, delay a second input time signal by a fixed amount, and output the delayed first and second input time signals respectively as either first and second output time signals or second and first output time signals, in accordance with the input data. The time-digital conversion circuit is configured to generate a digital output signal by comparing first and second output time signals from the last digital-time conversion circuit.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. An arithmetic apparatus for a neural network comprising: a plurality of digital-time conversion circuits connected in series, each of the digital-time conversion circuits being configured to delay a first input time signal by a variable amount, delay a second input time signal by a fixed amount, and output the delayed first and second input time signals respectively as either first and second output time signals or second and first output time signals, in accordance with the input data; and a time-digital conversion circuit connected to a last digital-time conversion circuit in the series, and configured to generate a digital output signal by comparing first and second output time signals from the last digital-time conversion circuit. 2. The arithmetic apparatus according to claim 1, wherein, in each of the digital-time conversion circuits, the input data is one-bit data, and when the input data is a first value, the delayed first input time signal is output as the first output time signal, and the delayed second input time signal is output as the second output time signal, and when the input data is not the first value, the delayed first input time signal is output as the second output time signal, and the delayed second input time signal is output as the first output time signal. 3. The arithmetic apparatus according to claim 2, wherein, in each of the digital-time conversion circuits, the first output time signal of an immediately previous digital-time conversion circuit, if any, is input as the first input time signal, and the second output time signal of the immediately previous digital-time conversion circuit, if any, is input as the second input time signal. 4. The arithmetic apparatus according to claim 1, wherein each of the digital-time conversion circuits includes a first input signal line through which the first input time signal is input, a second input signal line through which the second input time signal is input, a first output signal line through which the first output time signal is output, and a second output signal line through which the second output time signal is output. 5. The arithmetic apparatus according to claim 4, wherein, in each of the digital-time conversion circuits, the input data is one-bit data, and the digital-time conversion circuit includes a switching circuit configured to connect the first input signal line to the first output signal line and the second input signal line to the second output signal line, when the input data is a first value, and connect the first input signal line to the second output signal line and the second input signal line to the first output signal line, when the input data is not the first value. 6. The arithmetic apparatus according to claim 5, wherein each of the digital-time conversion circuits further includes a first delay circuit having a variable resistor and configured to delay the first input time signal by the variable amount, which corresponds to a resistance of the variable resistor, and a second delay circuit having a non-variable resistor and configured to delay the second input signal by the fixed amount, which corresponds to a resistance of the non-variable resistor. 7. The arithmetic apparatus according to claim 6, wherein, in each of the digital-time conversion circuits, the switching circuit includes a first switching element of a first type connected between the first input signal line and the first output signal line, a second switching element of a second type connected between the first input signal line and a second output signal line, a third switching elements of the second type connected between the second input signal line and the first output signal line, and a fourth switching element of the first type connected between the second input signal line and the second output signal line. 8. The arithmetic apparatus according to claim 1, wherein the time-digital conversion circuit outputs, as the digital output signal, the first output time signal from the last digital-time conversion circuit at a timing of transition of the second output time signal from the last digital-time conversion circuit. 9. The arithmetic apparatus according to claim 1, wherein the variable amount can be set to be larger than or smaller than the fixed amount. 10. The arithmetic apparatus according to claim 1, wherein each of the digital-time conversion circuits further includes a storage element and an XNOR circuit configured to carry out an XNOR operation on a value of data stored in the storage element and a value of the input data, a result of the XNOR operation being input to the digital-time conversion circuit as the input data. 11. A neural network comprising an input layer, an output layer, and one or more hidden layers provided between the input layer and the output layer, said one or more hidden layers including a plurality of arithmetic apparatuses, each of the arithmetic apparatuses comprising: a plurality of digital-time conversion circuits connected in series, each of the digital-time conversion circuits being configured to delay a first input time signal by a variable amount, delay a second input time signal by a fixed amount, and output the delayed first and second input time signals respectively as either first and second output time signals or second and first output time signals, in accordance with the input data; and a time-digital conversion circuit connected to a last digital-time conversion circuit in the series, and configured to generate a digital output signal by comparing first and second output time signals from the last digital-time conversion circuit. 12. The neural network according to claim 11, wherein, in each of the digital-time conversion circuits, the input data is one-bit data, and when the input data is a first value, the delayed first input time signal is output as the first output time signal, and the delayed second input time signal is output as the second output time signal, and when the input data is not the first value, the delayed first input time signal is output as the second output time signal, and the delayed second input time signal is output as the first output time signal. 13. The neural network according to claim 12, wherein, in each of the digital-time conversion circuits of each of the arithmetic apparatuses, the first output time signal of an immediately previous digital-time conversion circuit, if any, is input as the first input time signal, and the second output time signal of the immediately previous digital-time conversion circuit, if any, is input as the second input time signal. 14. The neural network according to claim 11, wherein, in each of the arithmetic apparatuses, each of the digital-time conversion circuits includes a first input signal line through which the first input time signal is input, a second input signal line through which the second input time signal is input, a first output signal line through which the first output time signal is output, and a second output signal line through which the second output time signal is output. 15. The neural network according to claim 14, wherein, in each of the digital-time conversion circuits of each of the arithmetic apparatuses, the input data is one-bit data, and the digital-time conversion circuit includes a switching circuit configured to connect the first input signal line to the first output signal line and the second input signal line to the second output signal line, when the input data is a first value, and connect the first input signal line to the second output signal line and the second input signal line to the first output signal line, when the input data is not the first value. 16. The neural network according to claim 15, wherein, in each of the arithmetic apparatuses, each of the digital-time conversion circuits further includes a first delay circuit having a variable resistor and configured to delay the first input time signal by the variable amount, which corresponds to a resistance of the variable resistor, and a second delay circuit having a non-variable resistor and configured to delay the second input signal by the fixed amount, which corresponds to a resistance of the non-variable resistor. 17. The neural network according to claim 16, wherein, in each of the digital-time conversion circuits of each of the arithmetic apparatuses, the switching circuit includes a first switching element of a first type connected between the first input signal line and the first output signal line, a second switching element of a second type connected between the first input signal line and a second output signal line, a third switching elements of the second type connected between the second input signal line and the first output signal line, and a fourth switching element of the first type connected between the second input signal line and the second output signal line. 18. The neural network according to claim 11, wherein, in each of the arithmetic apparatuses, the time-digital conversion circuit outputs, as the digital output signal, the first output time signal from the last digital-time conversion circuit at a timing of transition of the second output time signal from the last digital-time conversion circuit. 19. The neural network according to claim 11, wherein, in each of the arithmetic apparatuses, the variable amount can be set to be larger than and smaller than the fixed amount. 20. The neural network according to claim 11, wherein, in each of the arithmetic apparatuses, each of the digital-time conversion circuits further includes a storage element and an XNOR circuit configured to carry out an XNOR calculation of a value of data stored in the storage element and a value of the input data, a result of the XNOR calculation is input to the digital-time conversion circuit as the input data.