1. Technical Field of the Invention
The present invention relates in general to integrated circuitry, and in particular to complementary metal-oxide-semiconductor (CMOS) logic and circuits with enhanced speed characteristics.
2. Description of Related Art
For a number of reasons CMOS is the logic family of choice in today's VLSI devices. Due to the complementary nature of its operation, CMOS logic consumes near zero static power. CMOS also readily scales with technology. These two features are highly desirable given the drastic growth in demand for low power and portable electronic devices. Further, with the computer aided design (CAD) industry's focus on developing automated design tools for CMOS based technologies, the cost and the development time of CMOS VLSI devices has reduced significantly.
The one drawback of the CMOS logic family, however, remains its limited speed. That is, conventional CMOS logic has not achieved the highest attainable switching speeds made possible by modern sub-micron CMOS technologies. This is due to a number of reasons. Referring to
As a result of the speed limitations of conventional CMOS logic, integrated circuit applications in the Giga Hertz frequency range have had to look to alternative technologies such as ultra high speed bipolar circuits and Gallium Arsenide (GaAs). These alternative technologies, however, have drawbacks of their own that have made them more of a specialized field with limited applications as compared to silicon MOSFET that has had widespread use and support by the industry. In particular, compound semiconductors such as GaAs are more susceptible to defects that degrade device performance, and suffer from increased gate leakage current and reduced noise margins. Furthermore, attempts to reliably fabricate a high quality oxide layer using GaAs have not thus far met with success. This has made it difficult to fabricate GaAs FETs, limiting the GaAs technology to junction field-effect transistors (JFETs) or Schottky barrier metal semiconductor field-effect transistors (MESFETs). A major drawback of the bipolar technology, among others, is its higher current dissipation even for circuits that operate at lower frequencies.
It is therefore highly desirable to develop integrated circuit design techniques that are based on conventional silicon CMOS technology, but overcome the speed limitations of CMOS logic.
The present invention is directed to apparatus and methods of operation that are further described in the following Brief Description of the Several Views of the Drawings, the Detailed Description of the Invention, and the claims. Other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings.
The present invention provides ultra high-speed logic circuitry implemented in silicon complementary metal-oxide-semiconductor (CMOS) process technology. A distinction is made herein between the terminology “CMOS process technology” and “CMOS logic.” CMOS process technology as used herein refers generally to a variety of well established CMOS fabrication processes that form a field-effect transistor over a silicon substrate with a gate terminal typically made of polysilicon material disposed on top of an insulating material such as silicon dioxide. CMOS logic, on the other hand, refers to the use of complementary CMOS transistors (n-channel and p-channel) to form various logic gates and more complex logic circuitry, wherein zero static current is dissipated. The present invention uses current-controlled mechanisms to develop a family of very fast current-controlled CMOS (or C3MOS™) logic that can be fabricated using a variety of conventional CMOS process technologies, but that unlike conventional CMOS logic does dissipate static current. C3MOS logic or current-controlled metal-oxide-semiconductor field-effect transistor (MOSFET) logic are used herein interchangeably.
In a preferred embodiment, the basic building block of this logic family is an NMOS differential pair with resistive loads. Referring to
Significant speed advantages are obtained by this type of current steering logic. Unlike the conventional CMOS inverter of
The design of each C3MOS logic cell according to the present invention is optimized based on several considerations including speed, current dissipation, and voltage swing. The speed of the logic gate is determined by the resistive load and the capacitance being driven. As discussed above, the preferred embodiment according to the present invention uses polysilicon resistors to implement the load devices. P-channel MOSFETs can alternatively be used, however, they require special biasing to ensure they remain in linear region. Further, the junction capacitances of the p-channel load MOSFETs introduce undesirable parasitics. Speed requirements place a maximum limit on the value of the resistive loads. On the other hand, the various C3MOS logic cells are designed to preferably maintain a constant voltage swing (I×R). Accordingly, the values for R and I are adjusted based on the capacitive load being driven to strike the optimum trade-off between switching speed and power consumption.
The C3MOS logic family, according to the present invention, contains all the building blocks of other logic families. Examples of such building blocks include inverters, buffers, level shift buffers, N-input NOR and NAND gates, exclusive OR (XOR) gates, flip flops and latches, and the like.
A C3MOS master-slave flip-flop 800 according to the present invention can be made by combining two latches 700 as shown in
In
Every one of the logic gates described thus far may be implemented using p channel transistors. The use of p-channel transistors provides for various alternative embodiments for C3MOS logic gates.
As illustrated by the various C3MOS logic elements described above, all of the building blocks of any logic circuitry can be constructed using the C3MOS technique of the present invention. More complex logic circuits such as shift registers, counters, frequency dividers, etc., can be constructed in C3MOS using the basic elements described above. As mentioned above, however, C3MOS logic does consume static power. The static current dissipation of C3MOS may become a limiting factor in certain large scale circuit applications. In one embodiment, the present invention combines C3MOS logic with conventional CMOS logic to achieve an optimum balance between speed and power consumption. According to this embodiment of the present invention, an integrated circuit utilizes C3MOS logic for the ultra high speed (e.g., GHz) portions of the circuitry, and conventional CMOS logic for the relatively lower speed sections. For example, to enable an integrated circuit to be used in ultra high speed applications, the input and output circuitry that interfaces with and processes the high speed signals is implemented using C3MOS. The circuit also employs C3MOS to divide down the frequency of the signals being processed to a low enough frequency where conventional CMOS logic can be used. The core of the circuit, according to this embodiment, is therefore implemented by conventional CMOS logic that consumes zero static current.
An example of a circuit implemented using combined CMOS/C3MOS logic according to the present invention is shown in
Referring back to
As apparent from the circuit shown in
According to one embodiment of the present invention the combined C3MOS/CMOS circuit technique as shown in
In conclusion, the present invention provides various circuit techniques for implementing ultra high speed circuits using current-controlled CMOS (C3MOS) logic fabricated in conventional CMOS process technology. An entire family of logic elements including inverter/buffers, level shifters, NAND, NOR, XOR gates, latches, flip-flops and the like have been developed using C3MOS according to the present invention. In one embodiment, the present invention advantageously combines high speed C3MOS logic with low power conventional CMOS logic. According to this embodiment circuits such as transceivers along fiber optic channels can be fabricated on a single chip where the ultra-high speed portions of the circuit utilize C3MOS and the relatively lower speed parts of the circuit use conventional CMOS logic. While the above is a complete description of the preferred embodiment of the present invention, it is possible to use various alternatives, modifications and equivalents. Therefore, the scope of the present invention should be determined not with reference to the above description but should, instead, be determined with reference to the appended claims, along with their full scope of equivalents.
In addition, certain embodiments of the present invention provide a new family of CMOS logic that is based on current-controlled mechanism to maximize speed of operation. The current-controlled CMOS (or C3MOS™) logic family according to the present invention includes all the building blocks of any other logic family. The basic building block of the C3MOS logic family uses a pair of conventional MOSFETs that steer current between a pair of load devices in response to a difference between a pair of input signals. Thus, unlike conventional CMOS logic, C3MOS logic according to this invention dissipates static current, but operates at much higher speeds. In one embodiment, the present invention combines C3MOS logic with CMOS logic within the same integrated circuitry, where C3MOS is utilized in high speed sections and CMOS is used in the lower speed parts of the circuit.
Accordingly, in one embodiment, the present invention provides a current-controlled metal-oxide semiconductor field-effect transistor (MOSFET) circuit fabricated on a silicon substrate, including a clocked latch made up of first and second n-channel MOSFETs having their source terminals connected together, their gate terminals coupled to receive a pair of differential logic signals, respectively, and their drain terminals connected to a true output and a complementary output, respectively; a first clocked n-channel MOSFET having a drain terminal connected to the source terminals of the first and second n-channel MOSFETs, a gate terminal coupled to receive a first clock signal CK, and a source terminal; third and fourth n-channel MOSFETs having their source terminals connected together, their gate terminals and drain terminals respectively cross-coupled to the true output and the complementary output; a second clocked n-channel MOSFET having a drain terminal connected to the source terminals of the third and fourth n-channel MOSFETs, a gate terminal coupled to receive a second clock signal CKB, and a source terminal; first and second resistive elements respectively coupling the true output and the complementary output to a high logic level; and a current-source n-channel MOSFET connected between the source terminals of the first and second clocked n-channel MOSFETs and a logic low level.
In another embodiment, the circuit further includes a buffer/inverter made up of first and second n-channel MOSFETs having their source terminals connected together, their gate terminals respectively coupled to receive a pair of differential logic signals, and their drain terminals coupled to a high logic level via a respective pair of resistive loads; and a current-source n-channel MOSFET connected between the source terminals of the first and second n-channel MOSFETs and a low logic level, wherein, the drain terminal of the first n-channel MOSFET provides a true output of the buffer/inverter and the drain terminal of the second n-channel MOSFET provides the complementary output of the buffer/inverter.
In yet another embodiment, the present invention provides complementary metal-oxide-semiconductor (CMOS) logic circuitry that combines on the same silicon substrate, current-controlled MOSFET circuitry of the type described above for high speed signal processing, with conventional CMOS logic that does not dissipate static current. Examples of such combined circuitry include serializer/deserializer circuitry used in high speed serial links, high speed phase-locked loop dividers, and the like.
The present U.S. Utility Patent Application claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 1. U.S. Utility application Ser. No. 12/789,469, entitled “Current-controlled CMOS logic family,” (Attorney Docket No. BP1645C7), filed May 28, 2010, pending, which claims priority pursuant to 35 U.S.C. §120, as a continuation, and scheduled subsequently to be issued as U.S. Pat. No. 8,299,834 on Oct. 30, 2012, (as indicated in an ISSUE NOTIFICATION mailed from the USPTO on Oct. 10, 2012), to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 2. U.S. Utility application Ser. No. 12/784,713, entitled “Current-controlled CMOS logic family,” (Attorney Docket No. BP1645C6), filed May 21, 2010, pending, which claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 3. U.S. Utility application Ser. No. 12/363,202, entitled “Current-controlled CMOS logic family,” (Attorney Docket No. BP1645C5), filed Jan. 30, 2009, now U.S. Pat. No. 7,724,057 B2, issued on May 25, 2010, which claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 4. U.S. Utility application Ser. No. 11/729,679, entitled “Current-controlled CMOS logic family,” (Attorney Docket No. BP1645C4), filed Mar. 29, 2007, now U.S. Pat. No. 7,486,124 B2, issued on Feb. 3, 2009, which claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 5. U.S. Utility application Ser. No. 11/385,632, entitled “Current-controlled CMOS logic family,” (Attorney Docket No. BP1645C3), filed Mar. 21, 2006, now U.S. Pat. No. 7,215,169 B2, issued on May 8, 2007, which claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 6. U.S. Utility application Ser. No. 11/114,969, entitled “Current-controlled CMOS logic family,” (Attorney Docket No. BP1645C2), filed Apr. 26, 2005, now U.S. Pat. No. 7,038,516 B2, issued on May 2, 2006, which claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 7. U.S. Utility application Ser. No. 10/143,087, entitled “Current-controlled CMOS logic family,” (Attorney Docket No. BP1645C1), filed May 9, 2002, now U.S. Pat. No. 6,900,670 B2, issued on May 31, 2005, which claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 8. U.S. Utility application Ser. No. 09/484,856, entitled “Current-controlled CMOS logic family,” (Attorney Docket No. BP1645), filed Jan. 18, 2000, now U.S. Pat. No. 6,424,194 B1, issued on Jun. 23, 2002, which claims priority pursuant to 35 U.S.C. §119(e) to the following U.S. Provisional Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 8.1. U.S. Provisional Application Ser. No. 60/141,355, entitled “Current-controlled CMOS logic family,” (Attorney Docket No. BP1645), filed Jun. 28, 1999, now expired.
Number | Date | Country | |
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60141355 | Jun 1999 | US |
Number | Date | Country | |
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Parent | 12789469 | May 2010 | US |
Child | 13654158 | US | |
Parent | 12784713 | May 2010 | US |
Child | 12789469 | US | |
Parent | 12363202 | Jan 2009 | US |
Child | 12784713 | US | |
Parent | 11729679 | Mar 2007 | US |
Child | 12363202 | US | |
Parent | 11385632 | Mar 2006 | US |
Child | 11729679 | US | |
Parent | 11114969 | Apr 2005 | US |
Child | 11385632 | US | |
Parent | 10143087 | May 2002 | US |
Child | 11114969 | US | |
Parent | 09484856 | Jan 2000 | US |
Child | 10143087 | US |