# Patent

## Title
Circuitry and layouts for XOR and XNOR logic

## Abstract

An exclusive-or circuit includes a pass gate controlled by a second input node. The pass gate is connected to pass through a version of a logic state present at a first input node to an output node when so controlled. A transmission gate is controlled by the first input node. The transmission gate is connected to pass through a version of the logic state present at the second input node to the output node when so controlled. Pullup logic is controlled by both the first and second input nodes. The pullup logic is connected to drive the output node low when both the first and second input nodes are high. An exclusive-nor circuit is defined similar to the exclusive-or circuit, except that the pullup logic is replaced by pulldown logic which is connected to drive the output node high when both the first and second input nodes are high.

## Background
CLAIM OF PRIORITY
This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 61/174,408, filed Apr. 30, 2009, entitled “Circuitry and Layouts for XOR and XNOR Logic,” the disclosure of which is incorporated herein by reference in its entirety. This application is also a continuation-in-part application under 35 U.S.C. 120 of prior U.S. patent application Ser. No. 12/572,243, filed on Oct. 1, 2009, which is a continuation application under 35 U.S.C. 120 of prior U.S. patent application Ser. No. 12/212,562, filed Sep. 17, 2008, which is a continuation application under 35 U.S.C. 120 of prior U.S. application Ser. No. 11/683,402, filed Mar. 7, 2007, which claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 60/781,288, filed Mar. 9, 2006.


BACKGROUND
A push for higher performance and smaller die size drives the semiconductor industry to reduce circuit chip area by approximately 50% every two years. The chip area reduction provides an economic benefit for migrating to newer technologies. The 50% chip area reduction is achieved by reducing the feature sizes between 25% and 30%. The reduction in feature size is enabled by improvements in manufacturing equipment and materials. For example, improvement in the lithographic process has enabled smaller feature sizes to be achieved, while improvement in chemical mechanical polishing (CMP) has in-part enabled a higher number of interconnect layers.
In the evolution of lithography, as the minimum feature size approached the wavelength of the light source used to expose the feature shapes, unintended interactions occurred between neighboring features. Today minimum feature sizes are being reduced below 45 nm (nanometers), while the wavelength of the light source used in the photolithography process remains at 193 nm. The difference between the minimum feature size and the wavelength of light used in the photolithography process is defined as the lithographic gap. As the lithographic gap grows, the resolution capability of the lithographic process decreases.
An interference pattern occurs as each shape on the mask interacts with the light. The interference patterns from neighboring shapes can create constructive or destructive interference. In the case of constructive interference, unwanted shapes may be inadvertently created. In the case of destructive interference, desired shapes may be inadvertently removed. In either case, a particular shape is printed in a different manner than intended, possibly causing a device failure. Correction methodologies, such as optical proximity correction (OPC), attempt to predict the impact from neighboring shapes and modify the mask such that the printed shape is fabricated as desired. The quality of the light interaction prediction is declining as process geometries shrink and as the light interactions become more complex.
In view of the foregoing, solutions are sought for improvements in circuit design and layout that can improve management of lithographic gap issues as technology continues to progress toward smaller semiconductor device features sizes.
SUMMARY
In one embodiment, an exclusive-or (XOR) logic circuit is disclosed. The XOR logic circuit includes a first input node, a second input node, and an output node. A pass gate is connected to be controlled by a logic state present at the second input node. The pass gate is connected to pass through a version of a logic state present at the first input node to the output node when controlled to transmit by the logic state present at the second input node. A transmission gate is connected to be controlled by the logic state present at the first input node. The transmission gate is connected to pass through a version of the logic state present at the second input node to the output node when controlled to transmit by the logic state present at the first input node. Pullup logic is connected to be controlled by both the logic state present at the first input node and the logic state present at the second input node. The pullup logic is connected to drive a state present at the output node low when both the logic state present at the first input node and the logic state present at the second input node are high.
In one embodiment, an exclusive-or (XOR) logic circuit layout is disclosed. The XOR logic circuit layout includes six PMOS transistors and five NMOS transistors. The five NMOS transistors are respectively paired with five of the six PMOS transistors, such that each pair of NMOS and PMOS transistors is defined to share a contiguous gate electrode structure placed along a respective one of five gate electrode tracks. A sixth of the six PMOS transistors is defined by a gate electrode structure placed along a sixth gate electrode track, such that the sixth PMOS transistor does not share the sixth gate electrode track with another transistor within the exclusive-or logic circuit layout. The six gate electrode tracks are oriented parallel to each other.
In one embodiment, an exclusive-nor (XNOR) logic circuit is disclosed. The XNOR logic circuit includes a first input node, a second input node, and an output node. A pass gate is connected to be controlled by a logic state present at the second input node. The pass gate is connected to pass through a version of a logic state present at the first input node to the output node when controlled to transmit by the logic state present at the second input node. A transmission gate is connected to be controlled by the logic state present at the first input node. The transmission gate is connected to pass through a version of the logic state present at the second input node to the output node when controlled to transmit by the logic state present at the first input node. Pulldown logic is connected to be controlled by both the logic state present at the first input node and the logic state present at the second input node. The pulldown logic is connected to drive a state present at the output node high when both the logic state present at the first input node and the logic state present at the second input node are low.
In one embodiment, an exclusive-nor (XNOR) logic circuit layout is disclosed. The XNOR logic circuit layout includes five PMOS transistors and six NMOS transistors. The five PMOS transistors are respectively paired with five of the six NMOS transistors, such that each pair of PMOS and NMOS transistors is defined to share a contiguous gate electrode structure placed along a respective one of five gate electrode tracks. A sixth of the six NMOS transistors is defined by a gate electrode structure placed along a sixth gate electrode track, such that the sixth NMOS transistor does not share the sixth gate electrode track with another transistor within the exclusive-nor logic circuit layout. The six gate electrode tracks are oriented parallel to each other.
Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the present invention.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A shows a conventional XOR logic gate circuit;
FIGS. 1B-1E show state tables for the conventional XOR logic gate circuit of FIG. 1A;
FIG. 1F shows a layout of the conventional XOR, in accordance with one embodiment of the present invention;
FIG. 1G shows an example inverter configuration, in accordance with the prior art;
FIG. 2A shows an XNOR logic gate circuit, in accordance with one embodiment of the present invention;
FIGS. 2B-2E show state tables for the XNOR logic gate circuit of FIG. 2A, in accordance with one embodiment of the present invention;
FIG. 2F shows a layout of the XNOR logic gate circuit of FIG. 2A, in accordance with one embodiment of the present invention;
FIG. 3A shows an XOR logic gate circuit, in accordance with one embodiment of the present invention;
FIGS. 3B-3E show state tables for the XOR logic gate circuit of FIG. 3A, in accordance with one embodiment of the present invention;
FIG. 3F shows a layout of the XOR logic gate circuit of FIG. 3A, in accordance with one embodiment of the present invention;
FIG. 4A shows an example of gate electrode tracks defined within the restricted gate level layout architecture, in accordance with one embodiment of the present invention; and
FIG. 4B shows the exemplary restricted gate level layout architecture of FIG. 4A with a number of exemplary gate level features defined therein, in accordance with one embodiment of the present invention.



DETAILED DESCRIPTION
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.
Conventional XOR Circuit
FIG. 1A shows a conventional XOR logic gate circuit (“XOR 100” hereafter). The XOR 100 includes two inputs A and B, and one output Q. The input A is provided at a node 101. The input B is provided at a node 102. The output Q is provided at a node 105. FIGS. 1B-1E show state tables for the XOR 100. As shown in FIGS. 1B-1E, the XOR 100 provides an appropriate state of output Q for the various state combinations of inputs A and B.
As shown in FIG. 1A, the node 101 which receives the input A is connected to a gate of a PMOS transistor 117 and to a gate of an NMOS transistor 120. The node 101 is also connected to an input of an inverter 110. An output of the inverter 110 is connected to a node 103. The node 103 is connected to a gate of a PMOS transistor 113 and to a gate of an NMOS transistor 116.
The node 102 is connected to a gate of a PMOS transistor 114 and to a gate of an NMOS transistor 119. The node 102 is also connected to an input of an inverter 111. An output of the inverter 111 is connected to a node 104. The node 104 is connected to a gate of an NMOS transistor 115 and to a gate of a PMOS transistor 118.
The PMOS transistors 113 and 114 are connected in a serial manner between a power supply (VDD) and the node 105, which provides the XOR 100 output Q. The NMOS transistors 115 and 116 are connected in a serial manner between the node 105 and a reference ground potential (GND). The PMOS transistors 117 and 118 are connected in a serial manner between the power supply (VDD) and the node 105. The NMOS transistors 119 and 120 are connected in a serial manner between the node 105 and the reference ground potential (GND).
Based on the foregoing, the conventional XOR 100 includes two sets of pullup logic, where the first set is defined by PMOS transistors 113 and 114, and the second set is defined by PMOS transistors 117 an 118. The XOR 100 also includes two sets of pulldown logic, where the first set is defined by NMOS transistors 115 and 116, and the second set is defined by NMOS transistors 119 and 120. Each set of pullup and pulldown logic is controlled by both a version of the input A and a version of the input B. Therefore, based on the inputs A and B, the circuitry of the conventional XOR 100 is defined to drive the output Q either high or low by use of either set of pullup logic or either set of pulldown logic, respectively.
Additionally, it should be understood that each of inverters 110 and 111 includes one PMOS transistor and one NMOS transistor. FIG. 1G shows an example inverter configuration, in accordance with the prior art. The inverter receives an input signal A and produces an output signal Q. The inverter includes a PMOS transistor 192 having a gate connected to be controlled by the input signal A, a first terminal connected to a power supply (VDD), and a second terminal connected to provide the output signal Q. The inverter also includes an NMOS transistor 193 having a gate connected to be controlled by the input signal A, a first terminal connected to provide the output signal Q, and a second terminal connected to a reference ground potential (GND). When the input A of the inverter is high the output is low, vice-versa. Based on each inverter including one PMOS transistor and one NMOS transistor, it should be understood that the conventional XOR 100 includes a total of 6 PMOS transistors and 6 NMOS transistors.
FIG. 1F shows a layout of the XOR 100, in accordance with one embodiment of the present invention. The layout of the XOR 100 is defined in accordance with a restricted gate level layout architecture, as described herein. The various PMOS and NMOS transistors as previously described with regard to FIG. 1A are labeled accordingly in the layout of FIG. 1F. The various nodes as previously described with regard to FIG. 1A are also labeled accordingly in the layout of FIG. 1F. The gate electrodes of the PMOS transistor 118 and NMOS transistor 119 are defined in a co-linear manner such that they are separated within gate the level by an end-to-end spacing 195. Also, the gate electrodes of the PMOS transistor 114 and NMOS transistor 115 are defined in a co-linear manner such that they are separated within gate the level by an end-to-end spacing 196.
It should be understood that in order to layout the conventional XOR 100 within six gate electrode tracks using the restricted gate level architecture, it is necessary to have at least two gate electrode end-to-end spacings, e.g., 195 and 196, within the gate level of the XOR 100. Such end-to-end gate electrode spacings are defined in accordance with applicable design rules which require a minimum end-to-end spacing size. Therefore, it should be appreciated that the presence of end-to-end gate electrode spacings can require the P-type and N-type diffusion regions to be separated more than what would be required in the absence of end-to-end gate electrode spacings, thereby requiring a larger overall cell height.
XOR Circuit and Layout Embodiments
FIG. 3A shows an XOR logic gate circuit 300 (“XOR 300” hereafter), in accordance with one embodiment of the present invention. The XOR 300 includes two inputs A and B, and one output Q. The input A is provided at a node 301. The input B is provided at a node 302. The output Q is provided at a node 307. FIGS. 3B-3E show state tables for the XOR 300, in accordance with one embodiment of the present invention. As shown in FIGS. 3B-3E, the XOR 300 provides an appropriate state of output Q for the various state combinations of inputs A and B.
As shown in FIG. 3A, the node 301 which receives the input A is connected to both an input of an inverter 310 and to a gate of a PMOS transistor 314. The node 302 which receives the input B is connected to an input of an inverter 311. The output of the inverter 310 is connected to a node 303. The node 303 is connected to: 1) a first terminal of an NMOS transistor 312, 2) a gate of a PMOS transistor 316, and 3) a gate of an NMOS transistor 313. The output of the inverter 311 is connected to a node 304. The node 304 is connected to: 1) a gate of the NMOS transistor 312, 2) a gate of a PMOS transistor 315, 3) a first terminal of the NMOS transistor 313, and 4) a first terminal of the PMOS transistor 314.
A node 305 is connected to each of: 1) a second terminal of the NMOS transistor 312, 2) a second terminal of the NMOS transistor 313, 3) a second terminal of the PMOS transistor 314, and 4) a second terminal of the PMOS transistor 316. A first terminal of the PMOS transistor 315 is connected to a power supply (VDD). A second terminal of the PMOS transistor 315 is connected to a node 306, which is connected to an first terminal of the PMOS transistor 316. The node 305 is connected to an input of an inverter 317. An output of the inverter 317 is connected to a node 307, which provides the output Q of the XOR 300.
The state tables of FIGS. 3B-3E show the different states of the various nodes (Node-301 through Node-307) of the XOR 300 for application of different state combinations at the inputs A and B. Each of inverters 310, 311, and 317 includes one PMOS transistor and one NMOS transistor. Therefore, in contrast to the conventional XOR 100 that includes a total of six PMOS transistor and six NMOS transistors, the XOR 300 includes a total of six PMOS transistors and five NMOS transistors, thereby saving one NMOS transistor.
The 2-input XOR 300 is defined to process four unique combinations of inputs A and B, as depicted in FIGS. 3B-3E. Specifically, the NMOS transistor 313 and PMOS transistor 314 together define a transmission gate 350 which is controlled by the input A. When the state of input A is low, i.e., a logical 0, the transmission gate 350 contributes to control of the state of output Q, such that the state of output Q matches the state of input B. The NMOS transistor 312 defines a pass gate 360 which is controlled by the input B. When the state of input B is low, i.e., logical 0, the pass gate 360 contributes to control of the state of output Q, such that the state of output Q matches the state of input A.
The PMOS transistors 315 and 316 together define pullup logic 370 which is controlled by both of the inputs A and B. When both the state of input A and the state of input B are high, i.e., logical 1, both the transmission gate 350 and pass gate 360 are disabled, and the pullup logic 370 controls the state of output Q, such that the state of output Q is low, i.e., a logical 0. When either state of inputs A and B is low, i.e., logical 0, the pullup logic 370 is disabled.
The XOR 300 is defined to either:

    
    
        pass through a version of the state of input A to the output Q by way of pass gate 360 controlled by input B,
        pass through a version of the state of input B to the output Q by way of a transmission gate 350 controlled by input A, or
        drive a state of the output Q low by way of pullup logic 370 under the control of both inputs A and B.
    
    


In accordance with the foregoing, the XOR logic circuit 300 includes the first input A node 301, the second input B node 302, and the output Q node 307. The pass gate 360 is connected to be controlled by a logic state present at the second input node 302. The pass gate 360 is connected to pass through a version of a logic state present at the first input node 301 to the output node 307 when controlled to transmit by the logic state present at the second input node 302. The transmission gate 350 is connected to be controlled by the logic state present at the first input node 301. The transmission gate 350 is connected to pass through a version of the logic state present at the second input node 302 to the output node 307 when controlled to transmit by the logic state present at the first input node 301. Pullup logic 370 is connected to be controlled by both the logic state present at the first input node 301 and the logic state present at the second input node 302. The pullup logic 370 is connected to drive a state present at the output node 307 low when both the logic state present at the first input node 301 and the logic state present at the second input node 302 are high.
FIG. 3F shows a layout of the XOR 300, in accordance with one embodiment of the present invention. In one embodiment, the layout of the XOR 300 is defined based on a restricted gate level layout architecture, as described herein. Inverter 310 is defined by a PMOS transistor 310P and an NMOS transistor 310N which share a contiguous gate electrode structure 310G defined along a single gate electrode track 380. Inverter 311 is defined by a PMOS transistor 311P and an NMOS transistor 311N which share a contiguous gate electrode structure 311G defined along a single gate electrode track 384. Inverter 317 is defined by a PMOS transistor 317P and an NMOS transistor 317N which share a contiguous gate electrode structure 317G defined along a single gate electrode track 385.
The PMOS transistor 315 of the pullup logic 370 and the NMOS transistor 312 of the pass gate 360 share a contiguous gate electrode structure 381G defined along a single gate electrode track 381. The PMOS transistor 316 of the pullup logic 370 and the NMOS transistor 313 of the transmission gate 350 share a contiguous gate electrode structure 382G defined along a single gate electrode track 382. The PMOS transistor 314 of the transmission gate 350 is defined along a single gate electrode track 383. The nodes 301-307 are defined in the XOR 300 layout by various combinations of contacts, interconnect structures (M1, M2), and vias (Via1), so as make the connections between the various transistors as shown in FIG. 3A.
It should be appreciated that the layout of the XOR 300, when defined in accordance with the restricted gate electrode architecture, is defined using six adjacent gate electrode tracks (380-385). In one embodiment, the six adjacent gate electrode tracks (380-385) are equally spaced apart. However, in another embodiment, different perpendicular spacings can be used to separate the six adjacent gate electrode tracks (380-385). Also, it should be appreciated that the layout of the XOR 300, when defined in accordance with the restricted gate electrode architecture, does not require placement of opposing gate electrode line ends. In other words, there are no gate electrode structures placed end-to-end along any given gate electrode track within the XOR 300 layout. Therefore, lithographic difficulties associated with manufacturing end-to-end spacings between gate electrode features is avoided.
Also, because there are no end-to-end gate electrode spacings positioned along a given gate electrode track between the P-type diffusion region and the N-type diffusion region, the perpendicular layout space between the P-type and N-type diffusion regions is not forced to comply with a minimum size requirement, as would be dictated by design rules associated with placement/manufacture of end-to-end gate electrode spacings. Thus, if desired in certain embodiments, the overall cell height of the XOR 300 layout, i.e., the perpendicular distance between VDD and GND, may be reduced by spacing the P-type and N-type diffusion regions closer together.
Additionally, although the exemplary embodiment of FIGS. 3A and 3F show the pullup logic 370 defined such that the gate of the PMOS transistor 315 is connected to the output of the second input inverter 311, and such that the gate of the PMOS transistor 316 is connected to the output of the first input inverter 310, it should be understood that the stack of PMOS transistors 315 and 316 can be reversed. Specifically, in one embodiment, the pullup logic 370 is defined such that the gate of the PMOS transistor 315 is connected to the output of the first input inverter 310, and such that the gate of the PMOS transistor 316 is connected to the output of the second input inverter 311.
XNOR Circuit and Layout Embodiments
FIG. 2A shows an XNOR logic gate circuit 200 (“XNOR 200” hereafter), in accordance with one embodiment of the present invention. The XNOR 200 includes two inputs A and B, and one output Q. The input A is provided at a node 201. The input B is provided at a node 202. The output Q is provided at a node 207. FIGS. 2B-2E show state tables for the XNOR 200, in accordance with one embodiment of the present invention. As shown in FIGS. 2B-2E, the XNOR 200 provides an appropriate state of output Q for the various state combinations of inputs A and B.
As shown in FIG. 2A, the node 201 which receives the input A is connected to both an input of an inverter 210 and to a gate of an NMOS transistor 214. The node 202 which receives the input B is connected to an input of an inverter 211. The output of the inverter 210 is connected to a node 203. The node 203 is connected to: 1) a first terminal of an PMOS transistor 212, 2) a gate of a PMOS transistor 213, and 3) a gate of an NMOS transistor 215. The output of the inverter 211 is connected to a node 204. The node 204 is connected to: 1) a gate of the PMOS transistor 212, 2) a gate of an NMOS transistor 216, 3) a first terminal of the PMOS transistor 213, and 4) a first terminal of the NMOS transistor 214.
A node 205 is connected to each of: 1) a second terminal of the PMOS transistor 212, 2) a second terminal of the PMOS transistor 213, 3) a second terminal of the NMOS transistor 214, and 4) a second terminal of the NMOS transistor 215. A first terminal of the NMOS transistor 216 is connected to a reference ground potential (GND). A second terminal of the NMOS transistor 216 is connected to a node 206, which is connected to a first terminal of the NMOS transistor 215. The node 205 is connected to an input of an inverter 217. An output of the inverter 217 is connected to a node 207, which provides the output Q of the XNOR 200. The state tables of FIGS. 2B-2E show the different states of the various nodes (Node-201 through Node-207) of the XNOR 200 for application of different state combinations at the inputs A and B. Each of inverters 210, 211, and 217 includes one PMOS transistor and one NMOS transistor. Therefore, the XNOR 200 includes a total of five PMOS transistors and six NMOS transistors.
The 2-input XNOR 200 is defined to process four unique combinations of inputs A and B, as depicted in FIGS. 2B-2E. Specifically, the PMOS transistor 213 and NMOS transistor 214 together define a transmission gate 250 which is controlled by the input A. When the state of input A is high, i.e., a logical 1, the transmission gate 250 contributes to control of the state of output Q, such that the state of output Q matches the state of input B. The PMOS transistor 212 defines a pass gate 260 which is controlled by the input B. When the state of input B is high, i.e., logical 1, the pass gate 260 contributes to control of the state of output Q, such that the state of output Q matches the state of input A.
The NMOS transistors 215 and 216 together define pulldown logic 270 which is controlled by both of the inputs A and B. When both the state of input A and the state of input B are low, i.e., logical 0, both the transmission gate 250 and pass gate 260 are disabled, and the pulldown logic 270 controls the state of output Q, such that the state of output Q is high, i.e., a logical 1. When either state of inputs A and B is high, i.e., logical 1, the pulldown logic 270 is disabled.
Based on the foregoing, the XNOR 200 is defined to either:

    
    
        pass through a version of the state of input A to the output Q by way of pass gate 260 controlled by input B,
        pass through a version of the state of input B to the output Q by way of a transmission gate 250 controlled by input A, or
        drive a state of the output Q high by way of pulldown logic 270 under the control of both inputs A and B.
    
    


In accordance with the foregoing, the XNOR logic circuit 200 includes the first input A node 201, the second input B node 202, and the output Q node 207. The pass gate 260 is connected to be controlled by a logic state present at the second input node 202. The pass gate 260 is connected to pass through a version of a logic state present at the first input node 201 to the output node 207 when controlled to transmit by the logic state present at the second input node 202. The transmission gate 250 is connected to be controlled by the logic state present at the first input node 201. The transmission gate 250 is connected to pass through a version of the logic state present at the second input node 202 to the output node 207 when controlled to transmit by the logic state present at the first input node 201. Pulldown logic 270 is connected to be controlled by both the logic state present at the first input node 201 and the logic state present at the second input node 202. The pulldown logic 270 is connected to drive a state present at the output node 207 high when both the logic state present at the first input node 201 and the logic state present at the second input node 202 are low.
FIG. 2F shows a layout of the XNOR 200, in accordance with one embodiment of the present invention. In one embodiment, the layout of the XNOR 200 is defined based on a restricted gate level layout architecture, as described herein. Inverter 210 is defined by a PMOS transistor 210P and an NMOS transistor 210N which share a contiguous gate electrode structure 210G defined along a single gate electrode track 280. Inverter 211 is defined by a PMOS transistor 211P and an NMOS transistor 211N which share a contiguous gate electrode structure 211G defined along a single gate electrode track 284. Inverter 217 is defined by a PMOS transistor 217P and an NMOS transistor 217N which share a contiguous gate electrode structure 217G defined along a single gate electrode track 285.
The NMOS transistor 216 of the pulldown logic 270 and the PMOS transistor 212 of the pass gate 260 share a contiguous gate electrode structure 281G defined along a single gate electrode track 281. The NMOS transistor 215 of the pulldown logic 270 and the PMOS transistor 213 of the transmission gate 250 share a contiguous gate electrode structure 282G defined along a single gate electrode track 282. The NMOS transistor 214 of the transmission gate 250 is defined along a single gate electrode track 283. The nodes 201-207 are defined in the XNOR 200 layout by various combinations of contacts, interconnect structures (M1, M2), and vias (Via1), so as make the connections between the various transistors as shown in FIG. 2A.
It should be appreciated that the layout of the XNOR 200, when defined in accordance with the restricted gate electrode architecture, is defined using six adjacent gate electrode tracks (280-285). In one embodiment, the six adjacent gate electrode tracks (280-285) are equally spaced apart. However, in another embodiment, different perpendicular spacings can be used to separate the six adjacent gate electrode tracks (280-285). Also, it should be appreciated that the layout of the XNOR 200, when defined in accordance with the restricted gate electrode architecture, does not require placement of opposing gate electrode line ends. In other words, there are no gate electrode structures placed end-to-end along any given gate electrode track within the XNOR 200 layout. Therefore, lithographic difficulties associated with manufacturing end-to-end spacings between gate electrode features is avoided.
Also, because there are no end-to-end gate electrode spacings positioned along a given gate electrode track between the P-type diffusion region and the N-type diffusion region, the perpendicular layout space between the P-type and N-type diffusion regions is not forced to comply with a minimum size requirement, as would be dictated by design rules associated with placement/manufacture of end-to-end gate electrode spacings. Thus, if desired in certain embodiments, the overall cell height of the XNOR 200 layout, i.e., the perpendicular distance between VDD and GND, may be reduced by spacing the P-type and N-type diffusion regions closer together.
It should be understood that the XOR 300 circuit and associated layout as described herein can be converted to an XNOR circuit and associated layout by removing the output inverter 317. In this converted configuration, the output node 307 becomes equivalent to the node 305, and the relationship between the output Q and the inputs A and B is the same as shown in the state tables of FIGS. 2B-2E for the XNOR 200.
It should also be understood that the XNOR 200 circuit and associated layout as described herein can be converted to an XOR circuit and associated layout by removing the output inverter 217. In this converted configuration, the output node 207 becomes equivalent to the node 205, and the relationship between the output Q and the inputs A and B is the same as shown in the state tables of FIGS. 3B-3E for the XOR 300.
Additionally, although the exemplary embodiment of FIGS. 2A and 2F show the pulldown logic 270 defined such that the gate of the NMOS transistor 216 is connected to the output of the second input inverter 211, and such that the gate of the NMOS transistor 215 is connected to the output of the first input inverter 210, it should be understood that the stack of NMOS transistors 216 and 215 can be reversed. Specifically, in one embodiment, the pulldown logic 270 is defined such that the gate of the NMOS transistor 216 is connected to the output of the first input inverter 210, and such that the gate of the NMOS transistor 215 is connected to the output of the second input inverter 211.
Restricted Gate Level Layout Architecture
As mentioned above, the XOR 300 and XNOR 200 circuits of the present invention can be implemented in a restricted gate level layout architecture within a portion of a semiconductor chip. For the gate level, a number of parallel virtual lines are defined to extend across the layout. These parallel virtual lines are referred to as gate electrode tracks, as they are used to index placement of gate electrodes of various transistors within the layout. In one embodiment, the parallel virtual lines which form the gate electrode tracks are defined by a perpendicular spacing therebetween equal to a specified gate electrode pitch. Therefore, placement of gate electrode segments on the gate electrode tracks corresponds to the specified gate electrode pitch. In another embodiment the gate electrode tracks are spaced at variable pitches greater than or equal to a specified gate electrode pitch.
FIG. 4A shows an example of gate electrode tracks 401A-401E defined within the restricted gate level layout architecture, in accordance with one embodiment of the present invention. Gate electrode tracks 401A-401E are formed by parallel virtual lines that extend across the gate level layout of the chip, with a perpendicular spacing therebetween equal to a specified gate electrode pitch 407. For illustrative purposes, complementary diffusion regions 403 and 405 are shown in FIG. 4A. It should be understood that the diffusion regions 403 and 405 are defined in the diffusion level below the gate level. Also, it should be understood that the diffusion regions 403 and 405 are provided by way of example and in no way represent any limitation on diffusion region size, shape, and/or placement within the diffusion level relative to the restricted gate level layout architecture.
Within the restricted gate level layout architecture, a gate level feature layout channel is defined about a given gate electrode track so as to extend between gate electrode tracks adjacent to the given gate electrode track. For example, gate level feature layout channels 401A-1 through 401E-1 are defined about gate electrode tracks 401A through 401E, respectively. It should be understood that each gate electrode track has a corresponding gate level feature layout channel. Also, for gate electrode tracks positioned adjacent to an edge of a prescribed layout space, e.g., adjacent to a cell boundary, the corresponding gate level feature layout channel extends as if there were a virtual gate electrode track outside the prescribed layout space, as illustrated by gate level feature layout channels 401A-1 and 401E-1. It should be further understood that each gate level feature layout channel is defined to extend along an entire length of its corresponding gate electrode track. Thus, each gate level feature layout channel is defined to extend across the gate level layout within the portion of the chip to which the gate level layout is associated.
Within the restricted gate level layout architecture, gate level features associated with a given gate electrode track are defined within the gate level feature layout channel associated with the given gate electrode track. A contiguous gate level feature can include both a portion which defines a gate electrode of a transistor, and a portion that does not define a gate electrode of a transistor. Thus, a contiguous gate level feature can extend over both a diffusion region and a dielectric region of an underlying chip level.
In one embodiment, each portion of a gate level feature that forms a gate electrode of a transistor is positioned to be substantially centered upon a given gate electrode track. Furthermore, in this embodiment, portions of the gate level feature that do not form a gate electrode of a transistor can be positioned within the gate level feature layout channel associated with the given gate electrode track. Therefore, a given gate level feature can be defined essentially anywhere within a given gate level feature layout channel, so long as gate electrode portions of the given gate level feature are centered upon the gate electrode track corresponding to the given gate level feature layout channel, and so long as the given gate level feature complies with design rule spacing requirements relative to other gate level features in adjacent gate level layout channels. Additionally, physical contact is prohibited between gate level features defined in gate level feature layout channels that are associated with adjacent gate electrode tracks.
FIG. 4B shows the exemplary restricted gate level layout architecture of FIG. 4A with a number of exemplary gate level features 409-423 defined therein, in accordance with one embodiment of the present invention. The gate level feature 409 is defined within the gate level feature layout channel 401A-1 associated with gate electrode track 401A. The gate electrode portions of gate level feature 409 are substantially centered upon the gate electrode track 401A. Also, the non-gate electrode portions of gate level feature 409 maintain design rule spacing requirements with gate level features 411 and 413 defined within adjacent gate level feature layout channel 401B-1. Similarly, gate level features 411-423 are defined within their respective gate level feature layout channel, and have their gate electrode portions substantially centered upon the gate electrode track corresponding to their respective gate level feature layout channel. Also, it should be appreciated that each of gate level features 411-423 maintains design rule spacing requirements with gate level features defined within adjacent gate level feature layout channels, and avoids physical contact with any another gate level feature defined within adjacent gate level feature layout channels.
A gate electrode corresponds to a portion of a respective gate level feature that extends over a diffusion region, wherein the respective gate level feature is defined in its entirety within a gate level feature layout channel. Each gate level feature is defined within its gate level feature layout channel without physically contacting another gate level feature defined within an adjoining gate level feature layout channel. As illustrated by the example gate level feature layout channels 401 A-1 through 401E-1 of FIG. 4B, each gate level feature layout channel is associated with a given gate electrode track and corresponds to a layout region that extends along the given gate electrode track and perpendicularly outward in each opposing direction from the given gate electrode track to a closest of either an adjacent gate electrode track or a virtual gate electrode track outside a layout boundary.
Some gate level features may have one or more contact head portions defined at any number of locations along their length. A contact head portion of a given gate level feature is defined as a segment of the gate level feature having a height and a width of sufficient size to receive a gate contact structure, wherein “width” is defined across the substrate in a direction perpendicular to the gate electrode track of the given gate level feature, and wherein “height” is defined across the substrate in a direction parallel to the gate electrode track of the given gate level feature. It should be appreciated that a contact head of a gate level feature, when viewed from above, can be defined by essentially any layout shape, including a square or a rectangle. Also, depending on layout requirements and circuit design, a given contact head portion of a gate level feature may or may not have a gate contact defined thereabove.
A gate level of the various embodiments disclosed herein is defined as a restricted gate level, as discussed above. Some of the gate level features form gate electrodes of transistor devices. Others of the gate level features can form conductive segments extending between two points within the gate level. Also, others of the gate level features may be non-functional with respect to integrated circuit operation. It should be understood that the each of the gate level features, regardless of function, is defined to extend across the gate level within their respective gate level feature layout channels without physically contacting other gate level features defined with adjacent gate level feature layout channels.
In one embodiment, the gate level features are defined to provide a finite number of controlled layout shape-to-shape lithographic interactions which can be accurately predicted and optimized for in manufacturing and design processes. In this embodiment, the gate level features are defined to avoid layout shape-to-shape spatial relationships which would introduce adverse lithographic interaction within the layout that cannot be accurately predicted and mitigated with high probability. However, it should be understood that changes in direction of gate level features within their gate level layout channels are acceptable when corresponding lithographic interactions are predictable and manageable.
It should be understood that each of the gate level features, regardless of function, is defined such that no gate level feature along a given gate electrode track is configured to connect directly within the gate level to another gate level feature defined along a different gate electrode track without utilizing a non-gate level feature. Moreover, each connection between gate level features that are placed within different gate level layout channels associated with different gate electrode tracks is made through one or more non-gate level features, which may be defined in higher interconnect levels, i.e., through one or more interconnect levels above the gate level, or by way of local interconnect features at or below the gate level.
It should be understood that the XOR 300 and XNOR 200 circuits and layouts as disclosed herein can be stored in a tangible form, such as in a digital format on a computer readable medium. For example, the layouts of the XOR 300 and/or XNOR 200 circuits as disclosed herein can be stored in a layout data file as one or more cells, selectable from one or more libraries of cells. The layout data file can be formatted as a GDS II (Graphic Data System) database file, an OASIS (Open Artwork System Interchange Standard) database file, or any other type of data file format suitable for storing and communicating semiconductor device layouts. Also, the multi-level layouts of the XOR 300 and/or XNOR 200 circuits can be included within a multi-level layout of a larger semiconductor device. The multi-level layout of the larger semiconductor device can also be stored in the form of a layout data file, such as those identified above.
Also, the invention described herein can be embodied as computer readable code on a computer readable medium. For example, the computer readable code can include the layout data file within which the XOR 300 and/or XNOR 200 circuit layouts are stored. The computer readable code can also include program instructions for selecting one or more layout libraries and/or cells that include the XOR 300 and/or XNOR 200 circuit layouts. The layout libraries and/or cells can also be stored in a digital format on a computer readable medium.
The computer readable medium mentioned herein is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include hard drives, network attached storage (NAS), read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and other optical and non-optical data storage devices. The computer readable medium can also be distributed over a network of coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.
Any of the operations described herein that form part of the invention are useful machine operations. The invention also relates to a device or an apparatus for performing these operations. The apparatus may be specially constructed for the required purpose, such as a special purpose computer. When defined as a special purpose computer, the computer can also perform other processing, program execution or routines that are not part of the special purpose, while still being capable of operating for the special purpose. Alternatively, the operations may be processed by a general purpose computer selectively activated or configured by one or more computer programs stored in the computer memory, cache, or obtained over a network. When data is obtained over a network the data maybe processed by other computers on the network, e.g., a cloud of computing resources.
The embodiments of the present invention can also be defined as a machine that transforms data from one state to another state. The data may represent an article, that can be represented as an electronic signal and electronically manipulate data. The transformed data can, in some cases, be visually depicted on a display, representing the physical object that results from the transformation of data. The transformed data can be saved to storage generally, or in particular formats that enable the construction or depiction of a physical and tangible object. In some embodiments, the manipulation can be performed by a processor. In such an example, the processor thus transforms the data from one thing to another. Still further, the methods can be processed by one or more machines or processors that can be connected over a network. Each machine can transform data from one state or thing to another, and can also process data, save data to storage, transmit data over a network, display the result, or communicate the result to another machine.
It should be further understood that the XOR 300 and XNOR 200 circuits and layouts as disclosed herein can be manufactured as part of a semiconductor device or chip. In the fabrication of semiconductor devices such as integrated circuits, memory cells, and the like, a series of manufacturing operations are performed to define features on a semiconductor wafer. The wafer includes integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At a substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define a desired integrated circuit device. Also, patterned conductive layers are insulated from other conductive layers by dielectric materials.
While this invention has been described in terms of several embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. Therefore, it is intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention.

## Claims

1. A circuit, comprising:
a first input node;
a second input node;
a common node;
a pass gate connected to be controlled by a logic state present at the second input node, the pass gate connected to pass through a version of a logic state present at the first input node to the common node when controlled to transmit by the logic state present at the second input node;
a transmission gate connected to be controlled by the logic state present at the first input node, the transmission gate connected to pass through a version of the logic state present at the second input node to the common node when controlled to transmit by the logic state present at the first input node; and
pullup logic connected to be controlled by both the logic state present at the first input node and the logic state present at the second input node, the pullup logic connected to drive a state present at the common node when both the logic state present at the first input node and the logic state present at the second input node are high.

2. The circuit as recited in claim 1, further comprising:
a first input inverter having an input connected to the first input node and an output connected to the pass gate; and
a second input inverter having an input connected to the second input node and an output connected to the transmission gate.

3. The circuit as recited in claim 2, wherein the pass gate is defined as an NMOS transistor having a gate connected to the output of the second input inverter such that an inverted version of the logic state present at the second input node is received at the gate of the NMOS transistor, and
wherein the NMOS transistor has a first terminal connected to the output of the first input inverter and a second terminal connected to the common node.

4. The circuit as recited in claim 3, wherein the NMOS transistor is connected to transmit when the logic state at the second input node is low, such that the logic state at the common node is opposite the logic state at the first input node.

5. The circuit as recited in claim 2, wherein the transmission gate is defined by an NMOS transistor and a PMOS transistor which each has a respective first terminal connected to the output of the second input inverter, and which each has a respective second terminal connected to the common node, and
wherein the PMOS transistor has a gate connected to the first input node, and wherein the NMOS transistor has a gate connected to the output of the first input inverter.

6. The circuit as recited in claim 5, wherein both the PMOS and NMOS transistors are connected to transmit when the logic state at the first input node is low, such that the logic state at the common node is opposite the logic state at the second input node.

7. The circuit as recited in claim 2, wherein the pullup logic is defined by a first PMOS transistor and a second PMOS transistor, wherein the first and second PMOS transistors are serially connected between a power supply and the common node.

8. The circuit as recited in claim 7, wherein a gate of the first PMOS transistor is connected to the output of the second input inverter, and wherein a gate of the second PMOS transistor is connected to the output of the first input inverter.

9. The circuit as recited in claim 7, wherein a gate of the first PMOS transistor is connected to the output of the first input inverter, and wherein a gate of the second PMOS transistor is connected to the output of the second input inverter.

10. The circuit as recited in claim 7, wherein both the first and second PMOS transistors are connected to transmit when the logic states at the first and second input nodes are both high, such that the logic state at the common node is driven high.

11. The circuit as recited in claim 1, wherein the circuit is defined within a semiconductor chip.

12. An exclusive-or logic circuit layout, comprising:
six PMOS transistors; and
five NMOS transistors,
wherein the five NMOS transistors are respectively paired with five of the six PMOS transistors such that each pair of NMOS and PMOS transistors is defined to share a contiguous gate electrode structure placed along a respective one of five gate electrode tracks,
wherein a sixth of the six PMOS transistors is defined by a gate electrode structure placed along a sixth gate electrode track, such that the sixth PMOS transistor does not share the sixth gate electrode track with another transistor within the exclusive-or logic circuit layout, and
wherein the six gate electrode tracks are oriented parallel to each other.

13. The exclusive-or logic circuit layout as recited in claim 12, wherein the exclusive-or logic circuit layout is devoid of co-linearly placed gate electrodes having and end-to-end spacing therebetween.

14. The exclusive-or logic circuit layout as recited in claim 12, wherein each gate electrode structure is defined as a linear structure having a substantially rectangular cross-section when viewed in an as-drawn state.

15. The exclusive-or logic circuit layout as recited in claim 12, wherein the six gate electrode tracks are equally spaced apart.

16. The exclusive-or logic circuit layout as recited in claim 12, wherein the exclusive-or logic circuit layout is recorded in a digital format on a computer readable medium.

17. The exclusive-or logic circuit layout as recited in claim 16, wherein the digital format is a data file format for storing and communicating one or more semiconductor device layouts.

18. The exclusive-or logic circuit layout as recited in claim 16, wherein the computer readable medium includes program instructions for accessing and retrieving the exclusive-or logic circuit layout in the digital format from the computer readable medium.

19. The exclusive-or logic circuit layout as recited in claim 18, wherein the program instructions for accessing and retrieving include program instructions for selecting a library, a cell, or both library and cell including the exclusive- or logic circuit layout in the digital format.

20. The circuit as recited in claim 1, further comprising:
an output inverter having an input connected to the common node, the output inverter also having an output connected to an output node of the circuit.

21. A circuit, comprising:
five PMOS transistors; and
four NMOS transistors,
wherein the four NMOS transistors are respectively paired with four of the five PMOS transistors such that each of the four pairs of NMOS and PMOS transistors is formed from a different one of four contiguous gate electrode structures,
wherein a fifth of the five PMOS transistors is formed from a first single-transistor gate electrode structure that forms only one transistor device,
wherein each of the four contiguous gate electrode structures and the first single-transistor gate electrode structure are oriented parallel to each other,
wherein a first of the four NMOS transistors and a first of the five PMOS transistors forms a first pair of the four pairs of NMOS and PMOS transistors and forms a first input inverter of the circuit, and
wherein a second of the four NMOS transistors and a second of the five PMOS transistors forms a second pair of the four pairs of NMOS and PMOS transistors and forms a second input inverter of the circuit.

22. The circuit as recited in claim 21, wherein the circuit is devoid of co-linearly placed gate electrode structures having and end-to-end spacing therebetween.

23. The circuit as recited in claim 21, wherein each of the four contiguous gate electrode structures and the first single-transistor gate electrode structure is defined as a respective linear-shaped structure.

24. The circuit as recited in claim 21, wherein each of the four contiguous gate electrode structures and the first single-transistor gate electrode structure is placed in accordance with a fixed centerline pitch.

25. The circuit as recited in claim 21, wherein the circuit is defined as part of an exclusive-or logic function circuit.

26. The circuit as recited in claim 21, wherein a third NMOS transistor of the four NMOS transistors and a third PMOS transistor of the five PMOS transistors forms a transmission gate connected to the second input inverter.

27. The circuit as recited in claim 26, wherein a fourth NMOS transistor of the four NMOS transistors forms a pass gate connected to the first input inverter.

28. The circuit as recited in claim 27, wherein a fourth PMOS transistor of the five PMOS transistors and a fifth PMOS transistor of the five PMOS transistors forms pullup logic connected to outputs of both the pass gate and the transmission gate.

29. The circuit as recited in claim 28, further comprising:
a sixth PMOS transistor; and
a fifth NMOS transistor,
wherein both the sixth PMOS transistor and fifth NMOS transistor are formed by a fifth contiguous gate electrode structure.

30. The circuit as recited in claim 29, wherein the fifth contiguous gate electrode structure is oriented parallel to each of the four contiguous gate electrode structures and the first single-transistor gate electrode structure.

31. The circuit as recited in claim 29, wherein the sixth PMOS transistor and the fifth NMOS transistor form an output inverter having an input connected to outputs of each of the transmission gate, the pass gate, and the pullup logic.