US 5,841,686 A · Dual-bank memory module with shared capacitors and R-C elements integrated into the module substrate

Abstract

A memory module has DRAM chips mounted on both a front and a back surface but decoupling capacitors mounted on only the front surface. Each decoupling capacitor is for suppressing current spikes from a pair of DRAM chips. The pair of DRAM chips includes a first DRAM chip on the same surface as the capacitor and a second DRAM chip opposite the first DRAM chip on the back surface of the module. The first DRAM chip belongs to a first bank while the second DRAM chip belongs to a second bank. Two RAS signals are for controlling access to the two banks. Since only one bank is accessed at any time, and access causes current spikes, only one bank and only one DRAM chip in the pair of DRAM chips creates a current spike at any time. Thus a capacitor can be shared between the two DRAM chips in the pair. The shared capacitor can be mounted next to or under one of the DRAM chips, or formed within the multi-layer substrate itself. Having capacitors on only one of the surfaces reduces the number of placement sequences required, reducing manufacturing cost.

Claims20

Dependent claims

A dual-bank memory module with shared capacitors comprising:

a substrate having wiring traces for conducting signals, the substrate also having power-supply traces and ground traces for connection to a power supply voltage and a ground voltage;
a plurality of leads along a bottom edge of the substrate, the plurality of leads including a power-supply lead and a ground lead and control leads and data leads, the plurality of leads for electrically connecting the dual-bank memory module to a system;
and
pairs of DRAM chips, coupled to the plurality of leads, each pair having a first DRAM chip from a first bank and a second DRAM chip from a second bank, each pair of DRAM chips sharing a capacitor coupled between power-supply and ground pins of the first and second DRAM chips;
wherein all capacitors are mounted on a first surface of the substrate and no capacitors are mounted on a second surface of the substrate, the second surface opposite the first surface.

2 more elements

A dual-sided, multi-bank memory module comprising:

a substrate for making electrical connection between memory chips mounted on a first surface and on a second surface of the substrate;
a plurality of external connecting leads on the substrate, the plurality of external connecting leads for connecting to a host system, the plurality of connecting leads including data leads and control leads;
a plurality of shared capacitors for suppressing current spikes, the plurality of capacitors mounted on the first surface but not mounted on the second surface of the substrate;
a first bank of memory chips for storing data, the first bank having first memory chips mounted on the substrate, the first bank driving data onto all of the data leads in response to the control leads;
a second bank of memory chips for storing data, the second bank having second memory chips mounted on the substrate, the second bank driving data onto all of the data leads in response to the control leads;
wherein the first and the second bank drive the same data leads but are controlled by the host system to not drive data simultaneously;
the plurality of capacitors, the first bank, and the second bank being arranged on the substrate into local groups, each local group having a first memory chip from the first bank and a second memory chip from the second bank and one capacitor, the one capacitor physically located closer to the first and second memory chips in the local group than to other memory chips,
whereby the one capacitor in each local group suppressing current spikes generated by the memory chips in the local group when the data in either the first bank or the second bank is accessed.

5 more elements

Dependencies are inferred from the claim text.

Dual-bank memory module with shared capacitors and R-C elements integrated into the module substrate

Life of this patent

Dual-bank memory module with shared capacitors and R-C elements integrated into the module substrate

Life of this patent

Abstract

Claims20