Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Clock or pulse waveform generating
Reexamination Certificate
1999-12-08
2001-11-06
Nuton, My-Trang (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Clock or pulse waveform generating
Reexamination Certificate
active
06313682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the generation and transmission of electrical pulses with desired waveforms, particularly in the context of automatic test equipment (ATE) pin drivers.
2. Description of the Related Art
Pin drivers are commonly used in automated test equipment systems to generate test signals in the form of digital or analog voltages for delivery to the input pins of a device under test (DUT). They may be used, for example, to test memory chips having many input pins. Proper waveshape and timing accuracy of the signal at the DUT-are primary objectives of the overall system design, and are figures of merit which distinguish between different available ATE systems.
Due to increasing system speeds, waveform fidelity has become harder to maintain. While a pin driver itself may be able to produce a pure, undegraded signal, various elements of the overall system have a detrimental effect on waveform fidelity. These include the board on which the pin driver is attached (commonly called the channel card), the relays used to direct the signal, and the connectors which transmit the signal to other boards. The large number of pins on test devices such as memory chips also leads to long signal paths. The net effect is to lower the bandwidth of the test pulse signals that are delivered to the DUT. Although the driver itself may produce crisp, clean pulses with sharp corners, the net effect of the signal path between the pin driver and the DUT is to round off the corners of the test pulses, causing the transitions between the pulse edges and the full scale pulse value to be slower and more gradual than is desired. This is illustrated in
FIG. 1
, in which the clean pulse
2
generated by the pin driver is indicated by a solid line, with the rounded corners
4
induced by the transmission system indicated by dashed lines.
Attempts to remediate the pulse degradation have typically been directed towards reducing the effects of the transmission system. For example, inductive tuning networks have been provided along the signal path to produce a ringing which compensates for the path's effect on the pulse shape. Another approach involves adding copper stubs to the circuit board with a characteristic impedance that matches that of the transmission elements. Efforts have also been made to develop improved relays whose effect on the final pulse delivered to the DUT is reduced. All of these approaches are directed at modifying the transmission system so as to reduce or compensate for its effects on the clean pulse, and require a significant modification to the channel card.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved way to deliver a sharp pulse signal to a DUT, without having to modify the transmission system or significantly impacting the channel card. It relies upon modifying the original pulse signal itself, rather than the transmission system, to generate the pulse with a pre-emphasis that compensates for the effects of the transmission system, so that the final pulse delivered to the DUT has a desired clean waveform.
The pre-emphasis is implemented with an active feedback circuit in the pulse forming circuitry that adds a pre-emphasis to the edges of the pulse, preferably causing leading and trailing edges of the pulse to overshoot by an amount that compensates for the rounding effect of the transmission system. The feedback circuit is preferably integrated together with the basic pulse forming circuit in a common integrated circuit (IC) chip, except for an off-chip circuit that is used to program the amount of pre-emphasis to be added.
In one embodiment the feedback circuit modifies the current drive to an output transistor from which the pulse is produced. It includes an amplifier that receives a feedback from the output pulse, and an RC circuit which causes the amplifier to produce a pre-emphasis current for the output transistor as an edge overshoot. A pair of amplifiers are preferably employed to provide positive and negative overshoots for the leading and trailing pulse edges.
These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.
REFERENCES:
patent: 5434446 (1995-07-01), Hilton et al.
patent: 5842155 (1998-11-01), Bryson et al.
patent: 5877647 (1999-03-01), Vajapey et al.
patent: 6054879 (2000-04-01), Meng
patent: 6130563 (2000-10-01), Pilling et al.
patent: 6137322 (2000-10-01), Ten Eyck
Donald G. Fink, Donal christiansen, “Integrated-Circuit Design”,Electronics engineers' Handbook, McGraw-Hill Book Company, Third Edition, pp. 8-53 to 8-54, 13-6 to 13-7, 13-23, 19-68.
Richard C. Dorf, “Communications”,The Electrical Engineering Handbook, Second Edition, CRC Press and IEEE Press, pp. 1520, 1522.
Cohen Stephen A.
Muller, Jr. Richard R.
Analog Devices Inc.
Koppel & Jacobs
Nuton My-Trang
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