A neuromorphic memory circuit including a memory cell with a programmable resistive memory element. A postsynaptic capacitor builds up a leaky integrate and fire (LIF) charge. An axon LIF pulse generator activates a LIF discharge path from the postsynaptic capacitor through the resistive memory element when the axon LIF pulse generator generates axon LIF pulses. A postsynaptic comparator compares the capacitor voltage to a threshold voltage and generates postsynaptic output pulses when the capacitor voltage passes the threshold voltage. The postsynaptic output pulses include a postsynaptic firing characteristic dependent on a frequency of the axon LIF pulses. A refractory circuit prevents the postsynaptic comparator from generating additional postsynaptic output pulses until a refractory time passes since a preceding postsynaptic output pulse. A training circuit adjusts the postsynaptic firing characteristic to match a target firing characteristic.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A neuromorphic memory circuit comprising: a memory cell including a resistive memory element programmable to a memory resistance; a postsynaptic capacitor to build up a leaky integrate and fire (LIF) charge at a charge rate over time, the postsynaptic capacitor including a capacitor voltage proportional to the LIF charge; an axon LIF pulse generator to activate a LIF discharge path from the postsynaptic capacitor through the resistive memory element when the axon LIF pulse generator generates axon LIF pulses; a postsynaptic comparator to compare the capacitor voltage to a threshold voltage and generate postsynaptic output pulses when the capacitor voltage passes the threshold voltage, the postsynaptic output pulses including a postsynaptic firing characteristic dependent on a frequency of the axon LIF pulses; a refractory circuit coupled to the postsynaptic comparator, the refractory circuit is configured to prevent the postsynaptic comparator from generating additional postsynaptic output pulses until a refractory time passes since a preceding postsynaptic output pulse; and a training circuit configured to adjust the postsynaptic firing characteristic to match a target firing characteristic, the postsynaptic firing characteristic includes a postsynaptic firing rate that rises from a postsynaptic threshold frequency along a postsynaptic curve slope that asymptotically approaches a postsynaptic maximum frequency, the target firing characteristic includes a target firing rate that rises from a target threshold frequency along a target curve slope that asymptotically approaches a target maximum frequency. 2. The neuromorphic memory circuit of claim 1, wherein the training circuit is configured to: adjust the refractory time of the refractory circuit such that the postsynaptic maximum frequency of the postsynaptic firing characteristic matches the target maximum frequency of the target firing characteristic; adjust the memory resistance of the resistive memory element such that the postsynaptic curve slope of the postsynaptic firing characteristic matches the target curve slope of the target firing characteristic; and adjust the charge rate of the postsynaptic capacitor such that the postsynaptic threshold frequency of the postsynaptic firing characteristic matches the target threshold frequency of the target firing characteristic. 3. The neuromorphic memory circuit of claim 1, further comprising a leak transistor coupled to the postsynaptic capacitor, the leak transistor configured to control the charge rate of the postsynaptic capacitor. 4. The neuromorphic memory circuit of claim 1, further comprising: a dendrite pulse generator coupled to the resistive memory element, the dendrite pulse generator configured to generate dendrite pulses in response to the postsynaptic output pulses; an axon spike timing dependent plasticity (STDP) pulse generator to generate an axon STDP pulse, the axon STDP pulse activates a STDP discharge path from the dendrite pulse generator through the resistive memory element when the axon STDP pulse generator generates the axon STDP pulse, the resistive memory element is programmed to the memory resistance by generating the dendrite pulses while the STDP discharge path is activated by the axon STDP pulse. 5. The neuromorphic memory circuit of claim 1, wherein the resistive memory element includes a phase change material. 6. The neuromorphic memory circuit of claim 5, wherein the phase change material has an electrical resistance and is programmable to a set state having a set electrical resistance and reset state having a reset electrical resistance at least a factor of 10 greater than the set electrical resistance, the phase change material includes an initial state having an initial electrical resistance between the set electrical resistance and the reset electrical resistance, the initial state is at a lower potential energy than the set state and the reset state such that the electrical resistance of the phase change material programmed to the set state or the reset state drifts toward the initial electrical resistance over time. 7. The neuromorphic memory circuit of claim 6, wherein the phase change material includes GexSbyTez, where a Ge atomic concentration x is within a range from 30% to 70%, a Sb atomic concentration y is within a range from 10% to 30%, and a Te atomic concentration z is within a range from 20% to 50%. 8. A neuromorphic memory circuit comprising: a memory cell array, each memory cell in the memory cell array including a resistive memory element programmable to a memory resistance; a postsynaptic capacitor coupled to a row of memory cells in the memory cell array, the postsynaptic capacitor to build up a leaky integrate and fire (LIF) charge at a charge rate over time, the postsynaptic capacitor including a capacitor voltage proportional to the LIF charge; an axon LIF pulse generator coupled to a column of memory cells in the memory cell array, the axon LIF pulse generator to activate a LIF discharge path from the postsynaptic capacitor through the resistive memory element when the axon LIF pulse generator generates axon LIF pulses; a postsynaptic comparator to compare the capacitor voltage to a threshold voltage and generate postsynaptic output pulses when the capacitor voltage passes the threshold voltage, the postsynaptic output pulses including a postsynaptic firing characteristic dependent on a frequency of the axon LIF pulses; a refractory circuit coupled to the postsynaptic comparator, the refractory circuit is configured to prevent the postsynaptic comparator from generating additional postsynaptic output pulses until a refractory time passes since a preceding postsynaptic output pulse; and a training circuit configured to adjust the postsynaptic firing characteristic to match a target firing characteristic, the postsynaptic firing characteristic includes a postsynaptic firing rate that rises from a postsynaptic threshold frequency along a postsynaptic curve slope that asymptotically approaches a postsynaptic maximum frequency, the target firing characteristic includes a target firing rate that rises from a target threshold frequency along a target curve slope that asymptotically approaches a target maximum frequency. 9. The neuromorphic memory circuit of claim 8, wherein the training circuit is configured to, for each memory cell in the memory cell array: adjust the refractory time of the refractory circuit such that the postsynaptic maximum frequency of the postsynaptic firing characteristic matches the target maximum frequency of the target firing characteristic; adjust the memory resistance of the resistive memory element such that the postsynaptic curve slope of the postsynaptic firing characteristic matches the target curve slope of the target firing characteristic; and adjust the charge rate of the postsynaptic capacitor such that the postsynaptic threshold frequency of the postsynaptic firing characteristic matches the target threshold frequency of the target firing characteristic. 10. The neuromorphic memory circuit of claim 8, further comprising a leak transistor coupled to the postsynaptic capacitor, the leak transistor configured to control the charge rate of the postsynaptic capacitor. 11. The neuromorphic memory circuit of claim 8, further comprising: a dendrite pulse generator coupled to the row of resistive memory elements in the memory cell array, the dendrite pulse generator configured to generate dendrite pulses in response to the postsynaptic output pulses; an axon spike timing dependent plasticity (STDP) pulse generator coupled to the column of resistive memory elements in the memory cell array, the axon STDP pulse generator to generate an axon STDP pulse, the axon STDP pulse activates a STDP discharge path from the dendrite pulse generator through the resistive memory element when the axon STDP pulse generator generates the axon STDP pulse, the resistive memory element is programmed to the memory resistance by generating the dendrite pulses while the STDP discharge path is activated by the axon STDP pulse. 12. The neuromorphic memory circuit of claim 8, wherein each memory cell in the memory cell array includes a phase change material. 13. The neuromorphic memory circuit of claim 12, wherein the phase change material has an electrical resistance and is programmable to a set state having a set electrical resistance and reset state having a reset electrical resistance at least a factor of 10 greater than the set electrical resistance, the phase change material includes an initial state having an initial electrical resistance between the set electrical resistance and the reset electrical resistance, the initial state is at a lower potential energy than the set state and the reset state such that the electrical resistance of the phase change material programmed to the set state or the reset state drifts toward the initial electrical resistance over time. 14. The neuromorphic memory circuit of claim 13, wherein the phase change material includes GexSbyTez, where a Ge atomic concentration x is within a range from 30% to 70%, a Sb atomic concentration y is within a range from 10% to 30%, and a Te atomic concentration z is within a range from 20% to 50%. 15. The neuromorphic memory circuit of claim 8, wherein the refractory circuit is configured to prevent the capacitor voltage from passing the threshold voltage until the refractory time passes since the preceding postsynaptic output pulse. 16. A method for operating a neuromorphic memory circuit, the method comprising: accumulating a dendrite leaky integrate and fire (LIF) charge over time on a conductive dendrite LIF line, the conductive dendrite LIF line including a LIF voltage proportional to the LIF charge; generating axon LIF pulses, the axon LIF pulses activating a LIF discharge path from the conductive dendrite LIF line through a programmable resistive memory element; generating postsynaptic output pulses in response to the LIF voltage passing a threshold voltage; measuring a postsynaptic firing characteristic of the programmable resistive memory element over a range of axon LIF pulse frequencies, the postsynaptic firing characteristic includes a postsynaptic firing rate that rises from a postsynaptic threshold frequency along a postsynaptic curve slope that asymptotically approaches a postsynaptic maximum frequency; adjusting the postsynaptic firing characteristic to match a target firing characteristic, the target firing characteristic includes a target firing rate that rises from a target threshold frequency along a target curve slope that asymptotically approaches a target maximum frequency. 17. The method of claim 16, further comprising preventing the LIF voltage from passing the threshold voltage until a refractory time passes since a preceding output pulse. 18. The method of claim 17, wherein adjusting the postsynaptic firing characteristic includes: adjusting the refractory time such that the postsynaptic maximum frequency of the postsynaptic firing characteristic matches the target maximum frequency of the target firing characteristic; adjusting a memory resistance of the programmable resistive memory element such that the postsynaptic curve slope of the postsynaptic firing characteristic matches the target curve slope of the target firing characteristic; and adjusting the charge rate of the postsynaptic capacitor such that the postsynaptic threshold frequency of the postsynaptic firing characteristic matches the target threshold frequency of the target firing characteristic. 19. The method of claim 18, further comprising: generating dendrite pulses on a conductive dendrite spike timing dependent plasticity (STDP) line in response to the postsynaptic output pulses; and generating an axon STDP pulse, the axon STDP pulse activates a STDP discharge path from the dendrite STDP line through the programmable resistive memory element, the programmable resistive memory element is programmed to the memory resistance by generating the dendrite pulses while the STDP discharge path is activated by the axon STDP pulse. 20. The method of claim 16, wherein generating the postsynaptic output pulses includes comparing the LIF voltage to the threshold voltage.