Vlsi Technology, Inc.

James D Shiffer, Ii

Derwin W Mattos

Jeffrey F Wong

Mark R Hartoog

Daniel R Brasen

Sunil Asktaputre

An I/O buffer is provided that is noise-isolated, i.e., less susceptible to the effect of switching noise. In particular, a noise isolated I/O buffer includes an output terminal, a transient switching circuit connected to first power and ground voltage sources, to a logic input signal and to the output terminal, and a logic holding circuit connected to second power and ground voltage sources separate from the first power ground voltage sources, to the logic input signal and to the output terminal. The transient switching circuit causes a logic level of the output terminal to be switched responsive to a change in the input signal. The logic holding circuit causes the logic level of the output terminal to be maintained in the absence of a change in the input signal. In the absence of a change in the input signal, the transient switching circuit may be turned off, therefore presenting a high impedance to the first power and ground voltage sources. Switching noise in the first power supply network therefore is not transmitted through to the outputs of unswitched I/O buffers. The transient switching circuit and the logic holding circuit may be connected to the same power and ground voltage sources. The transient switching circuit, however, is turned off in the absence of a change in the input signal, and the logic holding circuit is turned off responsive to a change in the input signal. Smaller current surges are therefore provided at different times rather than a single large current surge, thereby reducing dI/dt. Provision is made for delaying turn on of the logic holding circuit until a logic transition of the output signal is substantially complete, further reducing the effects of switching noise on unswitched outputs. Preferably, the logic holding circuit, once it has been turned on, remains on despite possible changes in the output voltage level and is turned off only in response to changes in the input signal. The transient switching circuit may be constructed so as to, once it has been turned off, remain off despite possible changes in the output voltage level, or to turn back on in order to help return to output voltage to the proper level.

Noise isolated I/O buffer

An I/O buffer is provided that is noise-isolated, i.e., less susceptible to the effect of switching noise. In particular, a noise isolated I/O buffer includes an output terminal, a transient switching circuit connected to first power and ground voltage sources, to a logic input signal and to the output terminal, and a logic holding circuit connected to second power and ground voltage sources separate from the first power ground voltage sources, to the logic input signal and to the output terminal. The transient switching circuit causes a logic level of the output terminal to be switched responsive to a change in the input signal. The logic holding circuit causes the logic level of the output terminal to be maintained in the absence of a change in the input signal. In the absence of a change in the input signal, the transient switching circuit may be turned off, therefore presenting a high impedance to the first power and ground voltage sources. Switching noise in the first power supply network therefore is not transmitted through to the outputs of unswitched I/O buffers. The transient switching circuit and the logic holding circuit may be connected to the same power and ground voltage sources. The transient switching circuit, however, is turned off in the absence of a change in the input signal, and the logic holding circuit is turned off responsive to a change in the input signal. Smaller current surges are therefore provided at different times rather than a single large current surge, thereby reducing dI/dt.

Noise isolated I/O buffer that uses two separate power supplies

A transparent power grid is formed using a first metal layer and a second metal layer in a gate array having defined therein well tie-down regions. The first metal layer includes first power supply busses for supplying operating and reference voltages to the transistors, the first power supply busses extending in a row direction and overlapping the well tie-down region. The second metal layer includes second power supply busses for supplying operating and reference voltages to the transistors, the second power supply busses extending in a column direction and overlapping the well tie-down regions and the first power supply busses. Vias are formed where first and second power supply busses each supplying a same one of the operating voltage and the reference voltage overlap, thereby connecting the first and second power supply busses. Contacts are formed where first and second power supply busses each supplying a different one of the operating voltage and the reference voltage overlap, the contacts connecting the first power supply busses to underlying well tie-down regions. In effect, all of the necessary vias and contacts are placed in locations that in the prior art were all occupied by contacts alone.

Gate array bases with flexible routing

Flexible routing of gate arrays increases routing efficiency, provides for the routing of functional blocks with other gates in the gate array, and provides structures for flexible power routing, particularly of gate arrays having functional blocks. In particular, a gate-array-implemented integrated circuit is designed using a computer by representing in computer memory a gate array base, placing gate array cells on the gate array base in placement rows each having a uniform height and separated by routing channels in which no gate array cells are placed, and routing in the routing channel connections between placement rows according to a netlist, during routing increasing the size of a routing channel if required and decreasing the size of a routing channel if possible by changing the placement of at least one placement row by an amount less than half the height of the placement row. Routing channel size is therefore flexibly adjusted 'on-the-fly' during routing, increasing routing efficiency. The adjustment of routing channels in small (5 track) increments is made possible by defining 'tall' macros (four transistor rows high) made of 'small' (5 track high) transistors.

When a user requests a RAM or other semiconductor memory to be compiled with a number of rows that is not a power of two, the compiler creates the RAM with one extra row. The rows requested by the user are placed at contiguous row addresses starting at zero and ending at one less than the number of rows requested. The highest of these row addresses is placed permanently in a comparator by the compiler. The comparator then compares each row address input to the RAM to the row address contained in the comparator. If the row address input is higher, then the comparator selects the extra row. The extra row can be written into or read from in the same manner as any other row in the RAM. The delay of the comparator is comparable to the delay of the address decoder, so that the RAM operates within the same specifications regardless of whether the address decoder selects a row or the comparator selects the extra row.

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Fremont, CA, United States of America

James D Shiffer, Ii