Neuromorphic synapses

1. A method for producing a neuromorphic synapse apparatus having a desired weight-dependent synaptic update efficacy, the method comprising:

providing a memelement for storing a synaptic weight, the memelement being a phase-change memory cell adapted to exhibit a desired programming characteristic; and

providing programming logic, responsive to a stimulus prompting update of the synaptic weight, for generating a programming signal for programming the memelement to update said weight, each said programming signal comprising a respective set of n programming pulses applied at an input electrode of said phase-change memory cell;

configuring the programming logic to control at least one of the programming pulse shape and the value of n to such that the programming signals exploit said programming characteristic to provide said desired weight-dependent synaptic update efficacy.

2. The method according to claim 1 wherein the providing programming logic is responsive to an input signal indicating an input weight-change value, the method comprising:

adapting the programming logic to generate a programming signal dependent on the input weight-change value.

3. The method according to claim 2 further comprising:

implementing STDP logic for receiving pre-neuron and post-neuron action signals, and

adapting the STDP logic to generate said input weight-change value in dependence on time-difference between said action signals.

4. The method according to claim 2 , wherein the neuromorphic synapse apparatus includes an input terminal for receiving said input signal and an output terminal for providing a synaptic output signal dependent on said synaptic weight, the method further comprising:

adapting the programming logic to control the memelement for producing the synaptic output signal at the output terminal.

5. The method according to claim 1 , wherein the programming logic responds to an input signal indicating an input weight-change value, said method further comprising:

adapting the programming logic to generate a programming signal dependent on the input weight-change value, and wherein the dependence of the programming signal on the input weight-change value varies in a predetermined manner over a plurality of input weight-change values so as to provide the desired weight-dependent synaptic update efficacy.

6. The method according to claim 1 further comprising:

reconfiguring the programming logic in response to a control signal for dynamically varying the desired weight-dependent synaptic update efficacy.

7. The method according to claim 1 wherein the memelement has a modulated shape to provide said desired programming characteristic.

8. The method according to claim 1 wherein the memelement comprises a memristor.

9. The method according to claim 8 wherein the memelement comprises a resistive memory cell.

10. The method according to claim 9 wherein the cell comprises a resistive material located between first and second electrodes, and an electrically-conductive component extending in a direction between the electrodes in contact with the resistive material, and the method further comprising:

adapting the electrically-conductive component to provide said desired programming characteristic.

11. The method according to claim 9 , further comprising:

adapting the programming signals to effect peripheral crystallization of an amorphous volume of said phase-change material.

12. The method of claim 1 implemented in a neuromorphic system comprising a pre-neuron circuit for generating a pre-neuron action signal, a post-neuron circuit for generating a post-neuron action signal, and said neuromorphic synapse apparatus, wherein:

the synapse apparatus includes an output terminal connected to the post-neuron circuit; said method further comprising:

adapting the programming logic to control the memelement for producing a synaptic output signal, dependent on said synaptic weight, at the output terminal; and

said stimulus prompting update of the synaptic weight is dependent on the pre-neuron and post-neuron action signals.

13. The method according to claim 12 wherein:

the synapse apparatus further comprises STDP logic for receiving the pre-neuron and post-neuron action signals, the method further comprising:

adapting said STDP logic to generate an input weight-change value in dependence on time-difference between said action signals; and

adapting said programming logic to generate a said programming signal in response to said input weight-change value.