Electronic digital logic circuitry – Signal sensitivity or transmission integrity – Output switching noise reduction
Reexamination Certificate
2002-11-05
2004-08-17
Tan, Vibol (Department: 2819)
Electronic digital logic circuitry
Signal sensitivity or transmission integrity
Output switching noise reduction
C326S027000, C326S021000, C327S108000, C327S170000, C327S134000
Reexamination Certificate
active
06777974
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates first of all to an arrangement and to a method for adjustment of the slope times for one or more drivers essentially independently of external conditions. The invention also relates to a driver circuit and to advantageous applications.
2. Description of the Related Prior Art
Drivers and driver circuits are known, for example, as pad drivers for integrated circuits such as microcontrollers, microprocessors, ASICs, memory modules or the like and, to a major extent, govern the electromagnetic compatibility (EMC) of digital assemblies, for example of controller devices for motor vehicle or automation technology.
The relatively large current transients (dI/dt) which are required in order to charge and to discharge the generally capacitive loads, which are connected to the drivers, in a relatively short time to a specific voltage potential are a critical factor for such drivers and driver circuits. These times, which are referred to as the rise times (trise) and fall times (tfall) relate to the respectively rising and falling slope and are quoted for a specific maximum load in the specification for the driver. Normally, the driver strength is designed such that the driver comprises the guaranteed driver and timing characteristics in the worst permissible environmental conditions (referred to as the worst case).
For CMOS circuits, which are known per se, such worst case conditions are, for example, high ambient temperatures, low operating voltages, poor production parameters, that is to say production parameters which lead to “slow” switching times, and a maximum load, or the like. Since worst case conditions generally occur only rarely, the output slopes of conventional drivers designed in such a way are very much steeper than necessary, thus making the disturbance spectrum worse. The slope times—rise time/fall time—are likewise not constant either, owing to the possibility of the environmental conditions changing.
An ideal driver in terms of electromagnetic compatibility has the maximum permissible slope times, which are independent of external conditions, such as the ambient temperature, the operating voltage, the individual production parameters, and the connected load or the like. Furthermore, the maximum permissible slope times are dependent on the respective application of the drivers. For example, memory buses require a much shorter access time than, for example, input signals for an electrical switch (referred to as a smart power switch).
Experiments have shown that a significant improvement in the electromagnetic compatibility of output drivers can be achieved by reducing the driver strength and, associated with this, by increasing the slope times.
There is thus a need to be able to adjust the slope times of drivers individually.
DE-A-44 415 23 C1 discloses a digital driver circuit for an integrated circuit, in which the driver circuit can be matched to a specific application by the operator himself. Depending on the nature of the application, in this case depending on the load capacitance of a component which is to be operated using the driver circuit, this operator must enter an appropriate figure in an input apparatus. The figure is a variable which is dependent on the application. Physically, this circuit is a controller. The known solution assumes that variations in the environmental conditions can be established unambiguously by measuring the saturation current of a measurement transistor.
EP-A-0 436 316 A1 also specifies a circuit arrangement, which matches the impedance of a driver to a connected network. In this case, the circuit arrangement is intended to be suitable for being able to match itself to a load with an initially unknown impedance. To do this, the circuit arrangement has a driver with a predetermined impedance. An element for optional selection of an impedance is connected to the driver and, on operation, selectively causes changes to the predetermined impedance to match a desired, different impedance of the connected load. A further element is connected to this element for selection of the impedance. This element measures the impedance difference between the output of the driver and a digital circuit which is connected to it. A suitable impedance is selected on the basis of the measured values from the element for selection of the impedance, and is added to the predetermined, impedance, that is to say the preset impedance of the driver.
BRIEF SUMMARY OF THE INVENTION
One object of the present invention is to provide an improved arrangement, and a method for adjustment of slope times for one or more drivers, as well as an improved driver circuit, by means of which, in particular, the slope times for one or more drivers can be adjusted in a simple manner, and essentially independently of external conditions.
According to the first aspect of the invention, this object is achieved by an arrangement for adjustment of the slope times for one or more drivers essentially independently of external conditions, having an apparatus for recording the time profile of an output voltage which is emitted from the driver or drivers to a load, having an apparatus for conversion of the measured time profile of the output voltage to an output voltage value, having an apparatus for production of a reference voltage value, having a device for presetting a desired slope time, which is essentially independent of external conditions, for the driver or drivers, which device is connected to the apparatus for production of a reference voltage value, and having a device for comparison of the output voltage value with the reference voltage value, in which case the comparison device is or can be connected to the driver or drivers.
The arrangement according to the invention makes it possible to adjust the slope times for drivers independently of external conditions. In particular, it is possible to adjust the slope times for the drivers independently of the temperature, operating voltage, production process and load. These external conditions are enumerated purely way of example, so that the slope times can also be adjusted independently of other external conditions which are not explicitly mentioned in this enumeration.
The arrangement according to the invention means that one or more drivers is or are calibrated by a control cycle, which can preferably be repeated, such that the user of such a driver can adjust and set desired slope times, which can be selected within wide limits, largely independently of the external conditions.
The fundamental principle of the arrangement according to the invention is to generate a reference voltage value which corresponds to the desired slope time which can be programmed by the user. This reference voltage value is compared with an actually measured output voltage value. The driver or drivers is or are matched as a function of this comparison result.
When the driver or drivers is or are activated, the driver emits an output voltage. This output voltage is passed to a load. If the load which is connected to the driver or drivers is a load capacitance, this load capacitance is charged to an operating voltage Vdd on the basis of the output voltage which is emitted from the driver or drivers. When the driver or drivers is or are activated, the output voltage at the driver output will rise until the operating voltage Vdd is reached. An analogous situation applies to the converse case.
This time profile of the output voltage is recorded by the apparatus for recording the time profile, and this apparatus is specified in more detail further on in the description.
Since, in general, time values can be compared with one another only poorly, the measured time values are converted to an output voltage value in the apparatus for conversion of the measured time profile of the output voltage. This output voltage value can be temporarily stored.
At the same time, an appropriate reference voltage value is produced in the apparatus for production of a reference voltage value, whi
Eichfeld Herbert
Klein Ralf
Paulus Christian
Romer Dirk
Altera Law Group LLC
Infineon - Technologies AG
Stone Jeffrey R.
Tan Vibol
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