High speed memory module
A memory module may include a circuit board connectable to a system memory bus through a plurality of contacts disposed along one edge of the circuit board, the system memory bus having three positions for connecting memory modules. A plurality of memory chips may be mounted on the circuit board. The circuit board may include a plurality of D/Q traces to couple a corresponding plurality of D/Q signals from respective contacts to the plurality of memory chips or to one or more buffer chips that isolate the system memory bus from the memory chips. Each of the plurality of D/Q traces may have a predetermined trace impedance selected to provide a predetermined D/Q signal quality level when the memory module is installed in any of the three positions on the system memory bus and equivalent memory modules are installed in the other two positions.
1. A memory system, comprising:
a system memory bus
at least one memory module connected to the system memory bus, the memory module including at least one device, the device having at least one device D/Q (data input/output) terminal having a device output impedance when data is output from the memory module and a device input impedance when data is written into the memory module
a memory controller connected to the system memory bus, the memory controller having at least one controller D/Q terminal coupled to the device D/Q terminal via the system memory bus, the controller D/Q terminal having a controller output impedance when data is written into the memory module and a controller input impedance when data is read from the memory module
wherein a data signal propagates between the device D/Q terminal and the controller D/Q terminal as a primary signal via a direct path sequentially through a plurality of transmission line segments, each having a respective propagation delay and impedance, and as first and second reflected signals via first and second reflected paths
wherein the first and second reflected signals have opposite polarity and similar amplitude and the first and second reflected paths have similar propagation delays such that the first and second reflected signals destructively interfere.
2. The memory system of claim 1 , wherein:
the device output impedance, the device input impedance, the controller output impedance, the controller input impedance, and the impedances of the transmission line segments are collectively configured such that the first and second reflected signals have opposite polarity and similar amplitude.
3. The memory system of claim 1 , wherein:
the propagation delays of the plurality of transmission line segments are collectively configured such that the first reflected path and second reflected path have similar propagation delays.
4. The memory system of claim 1 , wherein the device is one of a memory chip and a buffer chip.
5. The memory system of claim 1 , wherein the plurality of transmission line segments includes a first segment in the memory module and a second segment in the system memory bus.
6. The memory system of claim 5 , wherein the first reflected path folds at a junction of the first segment and the second segment and folds at the device D/Q terminal
the second reflected path folds at the junction of the first segment and the second segment and folds at the controller D/Q terminal.