Static information storage and retrieval – Read/write circuit – Noise suppression
Reexamination Certificate
2000-10-24
2003-02-25
Elms, Richard (Department: 2824)
Static information storage and retrieval
Read/write circuit
Noise suppression
C365S226000, C365S227000
Reexamination Certificate
active
06525976
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to semiconductor integrated circuits, and more particularly, to systems and methods for reducing noise in mixed-mode semiconductor integrated circuits.
BACKGROUND OF THE INVENTION
In today's environment, semiconductors may contain both analog and digital components, commonly referred to as mixed signal or mixed-mode integrated circuits (ICs). The integration of analog and digital components on the same chip reduces costs, area and power requirements, which are important considerations in the manufacture of ICs. However, the combination of analog and digital components on the same substrate causes design challenges. Principally, switching noise from high-speed digital circuits easily interfere with and damage high-frequency analog circuits. Normally digital circuits switch quickly between predefined voltage levels, and consequently induce transient noise in power lines. Analog circuits what operate at a multiplicity of voltage levels and frequencies are sensitive to induced noise while the digital circuits are better able to withstand interference from induced noise.
Integrated circuits include a number of devices that are noise sensitive high performance devices. Fast changes in the charging or discharging of current can cause drops in voltage. This transient voltage can be large enough to interfere with the performance of these sensitive devices.
Substrate noise can affect numerous applications. For instance, substrate noise is a problem with phase-locked loop systems (PLLs) and inverters. PLLs are used in numerous applications including data recovery in disk drives, wired and wireless communications, high-speed microprocessors and memories.
Invertors (also referred to as flip-flops) are also widely used. Flip-flops serve important functions in reading and writing bits of words in memory devices. Normally, flip-flops encompass high-speed switching circuits that can be addressed to write or read into the flip-flop (need to define the flip-flop)
In a steady-state or quiescent condition, i.e. no switching occurring between output states, no current flows in the flip-flop from a power supply. Typically, the flip-flop includes a network of transistors connected to a power source and ground. In the steady-state condition, one transistor (or group of transistors) is turned on, and another transistor (or group of transistors) is turned off. To switch from one transistor to another, the power source switches from one state to another, for instance, from low to high which draws current. When one transistor is being turned off and the other transistor is being turned on, for a period of time, both transistors are on. During this period high current is present in the network. This high current causes a spike in voltage which introduces noise during the switching process. As the current is pulled through wires in the network, resistance is encountered and the voltage begins to drop and becomes a transient voltage throughout the IC. These transients can propagate along wires supplying power to the integrated circuit from the printed circuit board on which the integrated circuit board is mounted. The transients produce radio frequency (RF) radiation which can interfere with proper operation of other circuits on the printed circuit board as well as other circuits within the integrated circuit itself.
A number of prior attempts at solving switching noise problems have been proposed. One proposed solution focuses on controlling the current surge. U.S. Pat. No. 5,905,339 entitled “CMOS integrated circuit regulator for reducing power supply noise,” issued May 18, 1999, involves a complementary metal-oxide-semiconductor (CMOS) regulator which provides a constant current to a set of logic gates during the switching transition. This arrangement decouples the external supply shared by analog circuits and supplies current to supply rails. This current is kept nearly constant by a clamping action of clamping transistors. Excess charge for transient currents is supplied by a capacitor, which is replenished during non-switching times.
Another attempt to solve the noise problem involves the addition of decoupling capacitors placed near active devices. The decoupling capacitors stabilize the current flowing to these devices. However, while the capacitor absorbs some of the voltage, a spike still occurs.
Still another attempt to solve substrate noise problems involves an active method utilizing linear feedback loops. This approach involves sampling the noise at the analog receiver portion of the noise and directing that noise into an input stage of a negative feedback loop. After being amplified with reverse phase, the noise is re-injected into the substrate again. The re-injected noise, which has the opposite phase to that of the original noise traveling inside the substrate, may be used to cancel up to 83% of the original noise. This solution operates on mixed-mode integrated circuits operating at lower frequencies and low power portable electronics with slower digital clock speeds.
Yet another attempt to manage switching noise involve partitioning analog and digital functions. This process requires unique manufacturing processes and custom designs. For example, U.S. Pat. No. 6,020,614 entitled “Method of Reducing Substrate Noise Coupling in Mixed Signal Integrated Circuits,” issued Feb. 1, 2000, suggests that noise can be reduced by establishing boundary zones between the analog and digital circuits of a semiconductor substrate with the analog circuit having a separate power supply bus from the digital circuit. Further, this patent discloses providing interconnect signal lines such that the isolated wires between the circuits may functionally interact with other circuits while the substrate noise coupling from other circuits remains low. However, spacing the analog components from the digital components can waste precious semiconductor space, which is an important consideration in integrated circuit design.
Still another attempt to resolve switching noise problems is addressed in U.S. Pat. No. 5,649,160 entitled “Noise Reduction in Integrated Circuits and Circuit Assemblies,” issued Jul. 15, 1997. This patent suggests that the noise can be reduced by shaping the noise from the digital circuit and concentrating it in a single or a small number of parts of the frequency spectrum. This solution relies on the concept that the presence of noise in the analog circuit is less important at certain frequencies, and therefore the spectral peak or peaks from the digital circuit can be carefully placed to result in little or no interference.
The various prior attempts to solve the switching noise problems each have limitations. According, a need exists for systems and method to substantially reduce switching noise in mixed-mode integrated circuits.
SUMMARY OF THE INVENTION
This invention aims to overcome the problems associated with switching noise encountered in integrated circuits having analog and digital components by inclusion of a micro-battery on the integrated circuit. Noise arises in integrated circuits through several environments. Notably, noise is encountered when certain integrated circuits, such as inverters, transition from one logic state to another logic state. For example, inverter A must be turned on and inverter B must be turned off During the transition, for a period of time when both inverters are on while the transition completes. In this instance, a high current exists resulting in a spike in voltage and the introduction of noise.
An integrated circuit consistent with this invention that reduces switching noise includes an inverter network having at least two transistors, a gating network coupled to the inverter network, a micro-battery coupled to the inverter and a resistor coupled at one end to the micro-battery and connected to a power source at the other end. At steady state, the micro-battery is uncharged. When charged, nominal current flows through the micro-battery. When the inverter transitions, and the current surge occur
Baker, Donelson Bearman & Caldwell
Elms Richard
Excellatron Solid State LLC
Nguyen Hien
LandOfFree
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