Cypress Semiconductor Corporation

David Brian Rees

Martin Jonathon Steadman

Sandeep Pant

James W Lutley

Jonathan Withrington

A method and apparatus for functionality change in an integrated circuit chip includes bonding pads by which the functionality of the chip may be selected. Bonding pads are connected to a decoder which determines which path of a predetermined number of paths is to be chosen to provide the selected function. Control signals are fed to logic circuits in predetermined portions of the remainder of the integrated circuit chip to control functions of sub-circuits within the various portions of the integrated circuit chip.

Functionality change by bond optioning decoding

An integrated circuit or chip having a number of bond pads or inputs that may or may not have a bond wire connecting the pad to a supply voltage, ground or via a package pin to an external input when the chip is placed in the package. The circuits such as the input buffer connected to the pad are normally biased in the opposite voltage to that which the bond wire may be connected. For example, the input buffer circuitry connected to the bond pad, may see the pad as being connected to ground if the bond wires are connected, otherwise the input buffer circuitry will see the pad as being connected to VCC. When the pad is connected to a package pin then the end user may apply an electrical signal (e.g., supply voltage or ground) so that the integrated circuit may be configured as any one of a number of possible devices having one of a set of electrical attributes. Typically, the chip will have up to 8 such pads which can be used individually or in combination to configure the device. In one example, the chip would be part of an existing 'family' of chips which all have, for example, N package pins. The extra package pins used to configure the chip would be added to one or both ends of the package so that the rest of the package looks like a normal non-configurable member of the 'family'.

Universal logic chip

An output buffer includes a continuously variable output impedance proportional to the load transmission line impedance. The buffer includes an output stage, such as a pullup/pulldown transistor, for receiving an input signal and generating an output signal on an output node in response thereto. In addition, the buffer includes a control circuit and a low-impedance driver in an electrical communication with the output node and, preferably, disposed in parallel with at least one of the pullup and/or pulldown transistors. The control circuit receives the output node voltage and generates a control signal on a control node that varies according to the magnitude of the output node voltage. The driver is biased by the control signal and has a conductivity that varies according to the control signal. The variations in the conductivity are operative to adjust the output impedance of the buffer. The control circuit may include a voltage follower circuit that maintains an offset between the output node voltage and the control node voltage.

Transmission line impedance matching output buffer

A bi-directional control circuit for preventing the improper functioning of a pass transistor MN1 in a CMOS circuit due to abnormally high voltages on its source and drain nodes IO1 and IO2. If the voltage on one of the nodes, IO1 or IO2, rises with a fast input edge rate, tending to cause the gate voltage V1 to go too high due to capacitive coupling (source-gate or drain-gate), node N1 is coupled through an appropriate capacitor, C1 or C2, to another node N3, which is normally held low by a transistor MN9. The voltage on N3 drives the gate of a transistor MN10, connected to node N1, to pull the gate voltage V1 of MN1 low, tending to discharge the capacitive coupling due to the overlap capacitance of MN1, which tends to turn MN1 OFF and also allows the voltage V1 to decay very quickly, so as to prevent some of the charge from IO1 getting through to IO2.

Pass transistor capacitive coupling control circuit

An electrostatic discharge (ESD) protection circuit for an output transistor coupled to an I/O pin of an integrated circuit, including a logic circuit having at least one data input, a tristate enable input, and an tristate output coupled to a gate node of the output transistor wherein the tristate output is placed in a high impedance state in response to the tristate enable input. The ESD protection circuit also includes a tristate enable circuit which drives the tristate enable input according to the presence or absence of an ESD event on the I/O pin. During normal operation, the tristate enable circuit applies a first logic level to the tristate enable input such that the tristate output of the logic circuit is placed in a low impedance state, and during an ESD event on the I/O pin, the tristate enable circuit applies a second logic level to the tristate enable input such that the tristate output of the logic circuit is placed in a high impedance state.

ESD protection circuit for I/O buffers

The present invention concerns an output buffer, which overcomes previous disadvantages of driving transmission line loads by providing a variable output impedance in response to the load on the output. The buffer generally comprises a pullup device for providing a high voltage at the output in response to a first input, a pulldown device configured to provide a low voltage at the output in response to a second input and a second pulldown device configured to provide additional low drive at the output. The second pulldown device provides an impedance at the output which varies with respect to the voltage present at the output.

Output voltage controlled impedance output buffer

An augmentation circuit for use in connection with a self-bootstrap type output buffer having an n-channel pullup transistor is disclosed. The augmentation circuit includes a capacitor formed by a second n-channel transistor, connected as a capacitor, and disposed between first and second capacitor terminals. A non-overlapping signal generator is formed from a pair of NOR gates, and an inverter, to generate a pair of control signals CS1, and CS2 wherein when one of the control signals is active, the other control signal is inactive. Four n-channel transistors are provided in a switching matrix. One pair of the four n-channel transistors responds to control signal CS2 to connect the capacitor formed by the n-channel transistor across and between ground, and the output pad. In this switched configuration, a voltage level on the output pad is effectively impressed upon the capacitor, and is stored thereon. When an input signal to the buffer changes state to a logic high signal, the output of the control signals also change state, wherein the two n-channel transistors previously conducting, are now turned OFF, and the other two of the four n-channel transistors, which are controlled by CS1, are made to conduct. In this second switched configuration, the capacitor is connected across and between the positive power supply V.sub.cc, and a gate terminal of the pullup n-channel power supply. Accordingly, a voltage magnitude equal to V.sub.cc plus the pad voltage level stored on the capacitor is developed by the augmentation circuit and transferred to the gate of the pullup transistor. In another embodiment, a pair of transfer gates are used, which are controlled by a voltage level on the output node, to augment the input signal voltage level (using a stored level of approximately V.sub.cc). In a third low power embodiment, a capacitor (e.g. a p-channel device) is charged to V.sub.cc and is used to provide the required augmentation, as a function of the output node voltage.

Bootstrap augmentation circuit and method

An improved I/O cell is disclosed which includes a combined p-channel and n-channel transistor pullup configuration. In particular, such combination is connected in series between the chip operating voltage V.sub.cc, and the I/O cell output pad. The n-channel transistor is biased substantially continuously on its gate terminal with a pumped voltage from a charge pump, which permits it to pass voltages up to and including V.sub.cc. The p-channel transistor operates in its normal fashion, controllable via a pullup select signal applied to its gate terminal to pull the pad high. During normal operation, the n-channel transistor is always ON, thus reducing the substantial dynamic current drawn from the charge pump. The voltage appearing on the pad is fed back to a second n-channel transistor. When the voltage on the pad exceeds V.sub.cc for example, a 5 volt signal when V.sub.cc is 3.3 volts), the second n-channel transistor switches the gate of the first n-channel transistor to a reference signal, which is a diode drop below V.sub.cc. The first n-channel transistor, in response thereto, shuts-off, thus protecting the p-channel pullup transistor from the excessive voltages appearing on the pad.

High voltage-tolerant low voltage input/output cell

A method and apparatus to eliminate the problem of requiring sizing of the row and column decoders according to the pitch of the cells in the memory array is to decouple the decoder cell pitch from the memory cell pitch without causing the chip area to increase dramatically. Decoupling is accomplished by driving the array from both sides for row drivers and by driving the array from both the top and bottom for column drivers. This is achieved in one embodiment by driving alternating rows from opposite sides for row decoders. Even numbered rows are driven from one side and odd numbered rows are driven from the other side. Alternating columns are driven from both the top and bottom. For example, odd numbered columns are driven from the top while even numbered columns are driven from the bottom. In a second embodiment, predetermined rows are driven from one side while the others are driven from the other side. Similarly, predetermined columns may be driven from the top while the others are driven from the bottom. Rows 1 and 2 are driven from one side, rows 3 and 4 from the other, etc. Also, rows 1.about.3 may be driven from one side and rows 4.about.6 from the other. Columns 1 and 2 may be driven from the top, 3 and 4 from the bottom, 5 and 6 from the top, etc. Again, columns 1.about.3 may be driven from the top and columns 4.about.6 driven from the bottom.

Interdigitated memory array

An ultra-low power pumped n-channel transistor output buffer with self-bootstrapping includes an n-channel pullup transistor as the primary pullup device. A gate-to-source capacitance C.sub.gs of the pullup transistor is used to self-bootstrap the input data signal. A pass n-channel transistor is connected between the input data signal, and the gate of the pullup transistor, and is biased on a gate terminal thereof by a charge pump having a voltage magnitude one device threshold higher than the device operating rail V.sub.cc. The pass transistor, so biased, permits the input data signal, which may have a magnitude of V.sub.cc, to charge C.sub.gs. An over-voltage can be developed on the gate of the pullup transistor by the self-bootstrapping effect of C.sub.gs. The pass transistor, in addition, so biased, prevents such over-voltage on the pullup transistors gate from being shorted to V.sub.cc through a driving device. The output buffer also includes a p-channel transistor having source and drain terminals defining a channel that is connected between another pumped voltage rail, and the gate of the pullup transistor. This p-channel transistor is activated when the output on the pad is desired to be a logic one, and operates to replenish any charge lost on the bootstrap capacitance due to leakage on the gate of the pullup transistor, or from leakage on the drain of the pass transistor. A second capacitor, similar in size to the pass transistor capacitance, is connected between the gate of the pass transistor, and the gate of a pulldown n-channel transistor, and operates to equalize and reduce the effect of transition changes in the input data signal.

Ultra low power pumped n-channel output buffer with self-bootstrap

A method for varying the type of function selected on a chip (for example, after completion of manufacturing) may include the steps of providing predetermined fuse arrangements which individually or in combination correspond to each type of function on the chip and providing disable control lines having fuses to each of the predetermined fuse arrangements. When one of the types of circuits is selected, the predetermined fuse arrangement individually or in combination corresponding to that selected type of function is blown. The blowing of fuses may change the functionality of the chip directly or may perform a complex procedure such as controlling a portion of a decoding scheme which may radically change the function of the chip. To prevent further blowing of predetermined fuse arrangements, the fuses in disable control lines to each of the predetermined fuse arrangements may be blown, eliminating further selection of types of function.

Option decoding with on-chip electrical fuses

A bidirectional control circuit for preventing the improper functioning of a pass transistor MN1 in a CMOS circuit due to abnormally high voltages on its source and drain nodes IO1 and IO2. If the voltage on one of the nodes, IO1 or IO2, rises with a fast input edge rate, tending to cause the gate voltage V1 to go too high due to capacitive coupling (source-gate or drain-gate), node N1 is coupled through an appropriate capacitor, C1 or C2, to another node N3, which is normally held low by a transistor MN9. The voltage on N3 drives the gate of a transistor MN10, connected to node N1, to pull the gate voltage V1 of MN1 low, tending to discharge the capacitive coupling due to the overlap capacitance of MN1, which tends to turn MN1 OFF and also allows the voltage V1 to decay very quickly, so as to prevent some of the charge from IO1 getting through to IO2.

An output buffer having a reduced-swing output includes a p-channel pullup transistor as the primary pullup device. A biasing circuit is provided so as to bias the gate terminal of the pullup p-channel transistor to a predetermined level. The predetermined level is effective to cause the p-channel pullup transistor to shut off when the output of the buffer reaches a reduced magnitude output level (V.sub.OH). In the disclosed embodiment, the biasing circuit includes an n-channel transistor connected between the gate and drain terminals of the p-channel pullup transistor. The biasing circuit also includes a p-channel transistor having a source terminal connected to V.sub.cc, and a drain terminal connected to the gate of the pullup transistor. When the output of the buffer is desired to be in a logic high state, both of the biasing transistors are 'ON.' The voltage applied to the gate of the pullup transistor is, in effect, the result of the voltage divider effect between the 'ON' resistances of the two biasing transistors. These transistors divide the voltage between V.sub.cc and the voltage on the drain of the pullup transistor. A third p-channel transistor is provided, and which has a source terminal connected to V.sub.cc, and a drain terminal connected to the gate of the p-channel pullup transistor. This transistor is provided to turn the pullup transistor completely 'OFF' in predetermined situations, such as when a pulldown circuit is to be activated, or when the buffer is to be tri-stated.

Reduced output swing with p-channel pullup diode connected

Circuit for preventing the improper functioning of a CMOS output buffer that may occur due to the fact that since the output buffer P-channel may be coupled between a supply voltage and an output pad. If the pad is driven higher than the supply voltage by an external source, current may be injected into the parasitic diodes of the source/drain of the transistor.

5 Volt tolerant 3.3 volt output buffer

A bi-directional control circuit for preventing the improper functioning of a pass transistor MN1 in a CMOS circuit due to abnormally high voltages on its source and drain nodes IO1 and IO2, involves controlling the voltage V1 on gate of MN1 using a gate node N1 that is coupled to supply voltage VCC under the control of two transistor pairs MN3, MN4 and MP3, MP4 that sense the voltages on IO1 and IO2, and an inverter pair MP2, MN2 having a voltage signal ENB input on its gates. If the voltages on nodes IO1 and IO2 both go high, MP3 and MP4 tend to turn OFF dropping gate voltage V1, via MP2, below VCC and tending to turn MN1 OFF. Leakage from node N1 in such event occurs through a small current bleed network formed by three transistors MN6, MN7, and MN8.

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Overton, United Kingdom

David Brian Rees