DIMM memory module reference voltage switching circuit
A non-volatile memory module includes a volatile memory circuit; an interface to a reference voltage source external to the module providing an external reference voltage to the volatile memory circuit by which the volatile memory circuit and external devices may communicate reliably at high speeds; an internal reference voltage generator; and a control circuit adapted to cause the volatile memory circuit to be decoupled from using the external reference voltage and coupled to using a reference voltage from the internal reference voltage generator upon the non-volatile memory module ceasing to draw power from an external power source.
1. A non-volatile memory module comprising:
a volatile memory circuit;
an internal power source internal to the non-volatile memory module;
an external power interface to an external power source external to the non-volatile memory module;
an external reference voltage interface to an external reference voltage source external to the non-volatile memory module providing a first bus reference voltage to the volatile memory circuit to serve as a bus reference voltage for communications between the volatile memory circuit and devices external to the non-volatile memory module;
an internal reference voltage source providing a second bus reference voltage to the volatile memory circuit, the second bus reference voltage different than the first bus reference voltage;
a control circuit adapted to cause the volatile memory circuit to be decoupled from using the external reference voltage source and to be coupled to the internal reference voltage source in reaction to power loss at the external power interface; and
the control circuit further adapted to cause the volatile memory circuit to be decoupled from the internal reference voltage source and to be coupled to the external reference voltage source in reaction to power being applied at the external power interface.
2. The non-volatile memory module of claim 1 , further comprising a sample and hold circuit coupling the external reference voltage source to the non-volatile memory module and to the internal reference voltage source.