Electronic digital logic circuitry – Interface – Current driving
Patent
1997-04-28
2000-08-08
Tokar, Mike
Electronic digital logic circuitry
Interface
Current driving
326 86, 326 83, 326 30, 326 17, 326121, 326113, H03K 190175, H03K 19094
Patent
active
061007188
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electronic circuit for transmitting and/or processing signals, in particular digital signals, according to the precharacterizing clause of claim 1.
On account of the technical progress made in signal processing and the integration of electronic circuit components or circuits, also known as ICs for short, more and more digital signals have to be transmitted at in each case ever higher clock frequency between these circuits, for example in a television set. This means that more connecting lines are also required for the digital signal transmission.
With the conventional transmission standards, such as for example with TTL, CMOS and ECL levels, problems increasingly arise here with regard to the power consumption of the ICs on the one hand and to the disturbance of sensitive circuit components, such as for example sensitive receiving components of a television set, by radiated interference on the other hand.
Such disturbances can be avoided in many cases just by selected circuit arrangements or routing layouts. In other cases, however, additional screening measures against the radiated interference caused by the transmission of digital signals are also required.
It is the object of the invention to reduce the radiated interference in a transmission of digital signals.
This object is achieved by the invention specified in claim 1. Advantageous further developments of the invention are specified in the subclaims.
The invention is based on the idea of reducing the voltage swing between the signal levels high (H) and low (L) on the connecting lines each transmitting a data signal for a data transmission which has little radiated interference.
In principle, the aim here is for such a low-impedance input resistance of the respective signal input, receiving a digital signal, of a circuit transmitting and/or processing digital signals, which may be part of an IC, that the respective signal input can be current-controlled by the digital-signal source which is respectively assigned to it and is feeding it, or can be controlled with a small voltage level swing.
The input resistance is formed according to the invention by a transistor operated in gate connection and used as a signal input amplifier. The very high-impedance digital-signal source, respectively feeding a signal input via a connecting line, may be realized, for example, by an open-drain output.
The current controlling of the low-impedance signal input of a respective input amplifier with a high-impedance signal source in this case effects a small level swing, which for its part has the consequence of a drastically reduced radiated interference, in particular on the connecting lines each carrying a data signal.
The current controlling of the respective signal input has, furthermore, the consequence that the level swing, or at least one of the logic levels which are established at the signal input, can be determined by the circuit design of the respective signal input amplifier receiving a digital signal, it being not the input resistance which determines the voltage level but essentially the reference voltage at the gate of a field-effect transistor operated in gate connection, which is used for example as a signal input amplifier. For this reason, this principle of the current controlling of the signal input according to the invention is of outstanding significance for the transmission of digital signals between various ICs with CMOS technology, since this current controlling also permits between such ICs a digital signal transmission with a small level swing which has little radiated interference. Furthermore, it is ensured by this current controlling of the respective signal input that, for example, different earth potentials of ICs sending digital signals and receiving digital signals have no influence, within certain limits, on a detected signal level at the respective signal input of the IC receiving the digital signals.
The use of an open-drain output as the digital-signal source has, moreover, the advantage that a data tran
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patent: 3974404 (1976-08-01), Davis
patent: 5528190 (1996-06-01), Honnigford
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Blaud Phillppe
Rothermel Albrecht
Schweer Rainer
Deutsche Thomson-Brandt GmbH
Herrmann Eric P.
Kurdyla Ronald H.
Tan Vibol
Tokar Mike
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