Data processing: measuring – calibrating – or testing – Measurement system – Time duration or rate
Reexamination Certificate
2002-03-22
2004-03-02
Bui, Bryan (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Time duration or rate
C327S108000, C341S159000, C368S113000, C368S121000, C702S069000
Reexamination Certificate
active
06701280
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, an integrated circuit refers to an electrical circuit contained on a single monolithic chip containing active and passive circuit elements. As should be well understood in this art, integrated circuits are fabricated by diffusing and depositing successive layers of various materials in a preselected pattern on a substrate. The materials can include semiconductive materials such as silicon, conductive materials such as metals, and low dielectric materials such as silicon dioxide. The semiconductive materials contained in integrated circuit chips are used to form almost all of the ordinary electronic circuit elements, such as resistors, capacitors, diodes, and transistors.
Integrated circuits are used in great quantities in electronic devices such as digital computers because of their small size, low power consumption and high reliability. The complexity of integrated circuits ranges from simple logic gates and memory units to large arrays capable of complete video, audio and print data processing. Presently, however, there is a demand for integrated circuit chips to accomplish more tasks in a smaller space while having even lower operating voltage and power requirements.
Currently, the semiconductor industry is focusing its efforts on reducing dimensions within each individual integrated circuit in order to increase speed and to reduce energy requirements. The demand for faster and more efficient circuits, however, has created various problems for circuit manufacturers. For instance, a unique problem has emerged in developing equipment capable of characterizing, evaluating and testing faster chips. Timing errors and pulse width deviations may constitute a greater portion of a signal period at higher frequencies. As such, a need exists not only for devices capable of detecting these errors but also devices capable of characterizing and identifying these critical timing deviations.
In the past, electronic measurement devices have been used to test integrated circuits for timing irregularities by making frequency and period measurements of a signal output from the circuit. Certain devices, known as time interval analyzers or time counters, can perform time interval measurements, i.e. measurements of the time period between two input signal events, or can obtain other time characterizations of an input signal. A signal timing event is typically defined as the specific instant in time at which an input signal reaches a certain predefined level, also known as the threshold voltage level. At the specific time when the input signal crosses the threshold voltage level, a signal timing event occurs.
A time interval analyzer generally includes a continuous running clock and a continuous event counter. Typically, the device includes one or more timing measurement circuits on each of a plurality of measurement channels. Each measurement channel receives an input signal. By directing the signal across the channel to a given number of measurement circuits, known as interpolators, the device is able to measure the time interval between two events in the signals. Such devices are capable of making millions of measurements per second.
An alternative device for measuring timing parameters is a counter-based system. Similar to some extent to the time interval analyzer, a counter-based system measures the time period between two signal events using a clock that starts and then stops upon the respective signal events.
By measuring certain characteristics of a signal emitted by an integrated circuit, time interval analyzers and counter-based measurement devices can be used to detect timing errors or deviations that may be present within the circuit. This information can then be used to assist in developing an integrated circuit or for detecting defects in mass-produced circuits.
Timing fluctuations in integrated circuit signals are generally referred to as “jitter”. Jitter, broadly defined as a timing deviation between a real pulse train and an ideal pulse train, can be a deviation in phase and/or pulse width. Jitter typically refers to small variations caused by supply voltage fluctuations, control-system instability, temperature variation, noise and the like.
Instruments such as time interval analyzers, counter-based measurement devices and oscilloscopes have been used to measure jitter. In particular, time interval analyzers can monitor frequency changes and frequency deviation over time. In this manner, they not only detect jitter, but can also characterize jitter so that its source can be determined.
Further, devices such as time interval analyzers may be used to monitor single-ended or differential signals. Generally, single-ended signals are carried on a single cable and are referenced to ground or some other fixed voltage. Differential signals are carried on two cables and are referenced against each other. It may often be the case that the two signals are complements of each other. These two types of signals, single-ended and differential, have typically been monitored by distinctly configured pieces of equipment since each signal type requires a different type of input circuit and number of cables to detect it. Past measurement devices have thus typically been hard-wired during their manufacture for measurement of either single-ended or differential signals.
One possible way to switch between single-ended and differential signal inputs is by using a combination of electromechanical relays at the input to a time measurement device. However, relays within a signal path tend to introduce undesired capacitance to the signal path and often degrade high frequency performance of testing equipment. Thus, testing equipment with a minimum number of electromechanical relays in the input signal paths is highly desired.
As integrated circuits have grown more advanced, the need for differential signal measurements has grown. At the same time, the need to maintain the capability for single-ended measurement has remained. As a result, there is a need for a device capable of switching between single-ended and differential measurement modes that minimizes the number of component parts, as well as the number of relays in the path of the input signal.
In addition, most output signals from older generation integrated circuits emitted older digital signals where a binary “0” was a voltage between about 0 to 0.7 and binary “1” was about 4 to 5 volts. To test such signals, a simple single-ended input circuit with a single termination resistor to ground (0 volts) was used. In accordance with more modem technologies, output signals now exist with different voltage levels to represent logical “0” and “1”. For example, an LVDS output has logical “0” of 2.4 volts and logical “1” of 3.0 volts. In this case, the ideal input circuit would comprise a termination resistor connected to the range between logical “0” and “1”, such as 2.7 volts. So it is desired, for automatic test equipment to have an input termination voltage that is programmable by the user.
In addition, certain differential signals often need to be analyzed in a variety of fashions. One measurement mode involves comparing a differential signal against another differential signal such that the time difference between respective cross-over points can be determined. Another measurement mode involves measuring corresponding portions of a single signal in a differential pair to characterize rise time, fall time, undershoot and overshoot. Since individual signals in a differential pair may typically be related to each other, additional characterization of the levels of similarity between the two signals in the pair may also be desired. Due to the many types of desired measurements, it is preferred to have a time measurement unit, such as a time interval analyzer or a time counter, that is capable of measuring a differential signal in a differential fashion, and immediately thereafter in a single-ended fashion with a very close time interval between the two types of measurements. Such an application imposes the need to be a
Horne Steven
Kattan Shalom
Bui Bryan
Dority & Manning P.A.
Guide Technology
Le John
LandOfFree
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