DE10065741B4 - Procedure for determining crosstalk limits and for optimizing the unbundling of digital networks - Google Patents

Abstract

Method for determining at least one crosstalk limit value (ΔU_xtalk) of a crosstalk voltage (U_xtalk) from digital networks which have at least one digital transmitter with a high and a low state, and at least one digital receiver with a switching threshold (U_threshold) which has a maximum Has limit value (U_threshold_max) and a minimum limit value (U_threshold_min), whereby interference voltages are coupled into the digital networks, which largely consist of supply voltage fluctuations (ΔU_SSN_trans) at the transmitter, supply voltage fluctuations at the receiver (ΔU_SSN_rec) and the crosstalk voltage, characterized in that that
A voltage curve (U_in) at the receiver, during the transmission of digital signals between the transmitter and the receiver, is simulated,
A time axis of the voltage curve is divided into a plurality of areas which alternately describe a detection state (critical time window (Δt_krit_X)) and a waiting state of the receiver,
- the low state of the transmitter is simulated within at least one critical time window (Δt_krit_1) and a maximum low voltage (U_in_low max) of the voltage curve (U_in) is determined,
- within at least ...

Description

The invention relates to a method for determining at least one crosstalk threshold value of a crosstalk voltage of digital networks (circuits) that have at least one digital Transmitters, with a high and a low state, and at least one digital receiver, with a switching threshold that has a maximum and a minimum Has limit value included, interference voltages in the digital networks are coupled, for the most part from supply voltage fluctuations at the transmitter, supply voltage fluctuations at the recipient and the crosstalk voltage.

The invention further relates to a process for unbundling digital networks with digital components and conductor tracks, on at least one assembly, with between circuit creation and unbundling at least one crosstalk limit is determined.

When unbundling digital Assemblies and systems, that is, when transferring them Assemblies and systems in a physical design, is based on it paid attention that the elected Arrangement of the individual elements does not lead to interference with the circuit, such as for example due to a too small line spacing and large caused by this Crosstalk voltage. From I. Catt, "Crosstalk (Noise) in Digital Systems" IEEE Trans. Electromag. Compat., Volume EC-16, No. 6, pages 743-763, December 1967 is known that the crosstalk voltage coupled into individual digital networks certain limit (crosstalk limit) should not exceed the functionality of the circuit to ensure. From these, for example given by a circuit developer Limits, can then geometric rules are derived (line spacing, coupling length of the network segments running in parallel), which are used to unbundle the module or the system for correct function should be observed.

However, the choice is problematic of these crosstalk limits, because an excessively large crosstalk limit leads to one Danger the circuit functionality, too low a crosstalk limit draws very conservative geometric ones Rules that result in a large footprint on the Lead assembly.

• – eine technologisch maximale kapazitive und resistive Belastung des Treiberausgangs durch Terminierungen, Treibereingänge, Leitungswellenwiderstand, Pullup- und Pulldown-Widerstände, etc.;
• – eine pessimistisch große Reserve für die durch Schalten von Treibern, die sich im gleichen Gehäuse befinden, erzeugten Versorgungsspannungsschwankungen;
• – eine unverhältnismäßig große Unsicherheit der Schaltschwelle (zum Beispiel 0,8 V bis 2 V für TTL-Familien).

So far, the crosstalk limit value is usually determined in digital networks, for which there are no special requirements for a temporal jitter of edge transitions, by a DC signal-to-noise ratio (= "DC noise margin") of the block technology used, as described, for example, by MI Montrose in "EMC and the Printed Circuit Board - Design, Theory and Layout Made Simple "New York: IEEE Press 1998. However, this value is generally too conservative (too small) since it assumes" worst-case "assumptions, such as :

• - a technologically maximum capacitive and resistive load on the driver output due to terminations, driver inputs, line wave resistance, pull-up and pull-down resistors, etc .;
• - a pessimistic large reserve for the supply voltage fluctuations generated by switching drivers which are located in the same housing;
• - a disproportionately large uncertainty of the switching threshold (for example 0.8 V to 2 V for TTL families).

This also makes the geometric Rules for the unbundling very conservative, that is, the space required on the PCB is bigger than for the functionality would actually be necessary. This can in certain circumstances complex systems can not be realized because, for example Number of layers of the circuit board becomes too large.

In the published application DE 10025279A1 A method for component unbundling with minimization of crosstalk-induced radiation is proposed, in which the position of a conductor of a network that is exposed to a fault is determined in accordance with the crosstalk class of the own network and additionally the radiation class of the network causing the disturbance.

From US Patent 5,568,395 is a System for modeling and estimating crosstalk noise and for detecting false crosstalk induced noise logical results in a circuit known. The noise will through a causing signal network that is in a toggle state is, causes and affects a signal network that is in a non-switching state is. The valued Noise level is compared to a set threshold, to see if wrong logical results affected that Signal network are caused.

It is therefore an object of the invention to develop a process that makes it optimal for every digital network adapted Limit values of a crosstalk voltage (crosstalk limit values) determine.

Furthermore, it is an object of the invention a procedure for unbundling digital networks to that effect to further develop that available on an assembly standing space due to the geometric arrangement of conductor tracks and components can be optimally used.

These tasks are characterized by the characteristics of independent process claims.

The inventors have recognized that the on interference voltages coupled into a digital network only to one Circuit malfunction if one occurring at the receiver within a critical time window minimum voltage U_in_high_min in the high state of the driver under the Switching threshold of the receiver or if one occurs at the receiver within the critical time window maximum voltage U_in_low_max in the low state of the driver above the Switching threshold of the receiver lies. In such a case, the recipient can not clean between the High and low state, So differentiate between the voltage information of a digital "1" or "0". There the interference voltage essentially from supply voltage fluctuations at the transmitter and the recipient and there is a crosstalk voltage, the tolerable limit for the Crosstalk voltage can easily be calculated if the other parameters are known for this.

• – ein Spannungsverlauf am Empfänger bei der Übertragung von digitalen Signalen zwischen dem Sender und dem Empfänger simuliert wird,
• – eine Zeitachse des Spannungsverlaufs in eine Vielzahl von Bereichen aufgeteilt wird, die abwechselnd einen Detektionszustand (kritisches Zeitfenster) und einen Wartezustand des Empfängers beschreiben,
• – innerhalb mindestens eines kritischen Zeitfensters der Low-Zustand des Senders simuliert wird und hierbei eine maximale Spannung (maximale Low-Spannung) des Spannungsverlaufs ermittelt wird,
• – innerhalb mindestens eines anderen kritischen Zeitfensters der High-Zustand des Senders simuliert wird und hierbei eine minimale Spannung (minimale High-Spannung) des Spannungsverlaufs ermittelt wird, und
• – aus der minimalen High-Spannung, den Versorgungsspannungsschwankungen am Sender und am Empfänger und dem maximalen Grenzwert der Schaltschwelle und/oder aus der maximalen Low-Spannung, dem minimalen Grenzwert der Schaltschwelle des Empfängers und den Versorgungsspannungsschwankungen am Sender und am Empfänger der Nebensprechgrenzwert berechnet wird.

According to this inventive concept, the inventors propose a method for determining at least one crosstalk limit value of a crosstalk voltage of digital networks, which have at least one digital transmitter, with a high and a low state, and at least one digital receiver, with a switching threshold that has a maximum and has a minimum limit value, wherein interference voltages are coupled into the digital networks, which largely consist of supply voltage fluctuations at the transmitter, supply voltage fluctuations at the receiver and the crosstalk voltage. The further development of the method according to the invention is that:

• A voltage curve at the receiver is simulated during the transmission of digital signals between the transmitter and the receiver,
• A time axis of the voltage curve is divided into a plurality of areas which alternately describe a detection state (critical time window) and a waiting state of the receiver,
• - the low state of the transmitter is simulated within at least one critical time window and a maximum voltage (maximum low voltage) of the voltage curve is determined,
• - The high state of the transmitter is simulated within at least one other critical time window and a minimum voltage (minimum high voltage) of the voltage curve is determined, and
• - The crosstalk limit value is calculated from the minimum high voltage, the supply voltage fluctuations at the transmitter and receiver and the maximum limit value of the switching threshold and / or from the maximum low voltage, the minimum limit value of the switching threshold of the receiver and the supply voltage fluctuations at the transmitter and receiver ,

This ensures that for each digital network electrically permissible Crosstalk limit is determined, so that the usual manual allocation of conservative and network class-dependent crosstalk limits. The invention thus assigns an individual crosstalk limit to each network closed and is therefore no longer dependent on the network class. Advantageously offer the larger crosstalk limit values according to the invention now allow more space for component unbundling thus the realization of complex systems.

The simulation of the voltage curve at the recipient takes place here with conductor lengths and - Arrangements resulting from the planned network topology and placement of the components can be predicted and, for example, with the help of a common Simulation program carried out become. The order and type of links are shown under network topology of individual drivers, receivers and terminations ("star", "H-tree", "daisy chain") understood lengths of the individual segments of the network result approximately from the placement of the components on the assembly. Furthermore, that will Network preferably simulated without neighbors, because of the simulation the still allowed SNR should be calculated. Possibly already existing (= routed) Conductor tracks from neighboring networks can therefore simply be ignored so that no crosstalk limit is specified must become.

In an advantageous embodiment of the method according to the invention, a crosstalk limit value ΔU_xtalk_high is calculated in order to estimate the permissible crosstalk limit value in the high state of the transmitter, in that the amounts of the supply voltage fluctuations at the transmitter ΔU_SSN_trans and at the receiver ΔU_SSN_rec and the maximum limit value from the minimum high voltage U_in_high_min Switching threshold U_threshold_max are deducted according to: ΔU_xtalk_high = U_in_high_min - | ΔU_SSN_trans | - | ΔU_SSN_rec | - U_threshold_max. (1)

A further embodiment of the method according to the invention provides that a crosstalk limit value ΔU_xtalk_low is calculated to estimate the permissible crosstalk limit value in the low state of the transmitter, in that the amounts of the supply voltage fluctuations at the transmitter ΔU_SSN_trans and at the receiver ΔU_SSN_rec as well as from the minimum limit value of the switching threshold U_threshold_min the maximum low voltage U_in_low_max is subtracted to: ΔU_xtalk_low = U_threshold_min - | ΔU_SSN_trans | - | ΔU_SSN_rec | - U_in_low_max. (2)

In a particularly advantageous further development of the method according to the invention, the permissible crosstalk voltage U_xtalk is determined from the minimum of the crosstalk limit value ΔU_xtalk_low in the low state of the transmitter and the crosstalk limit value ΔU_xtalk_high in the high state of the transmitter according to: | U_xtalk | <min (ΔU_xtalk_low, ΔU_xtalk_high). (3)

In a further development of the method according to the invention becomes the size of the supply voltage fluctuations on the transmitter (ΔU_SSN_trans) and at the receiver (ΔU_SSN_rec) from an estimate receive. The estimate of ΔU_SSN_trans is now only based on the properties of the actually used Transmitter device. The estimate from ΔU_SSN_rec is now only based on the properties of the actually used Receiver module. So that it can be carried out more precisely as a network class dependent appraisal (with worst-case assumptions for the module type of the transmitter and the recipient), based on the establishment of the DC signal-to-noise ratio lies.

In addition, the size of the supply voltage fluctuations on the transmitter (ΔU_SSN_trans) and at the receiver (ΔU_SSN_rec) can be obtained from a simulation. Commercial programs can do this are used, which consist of the model data of the block and the used on the module power supply system, with its Abblockmaßnahmen, The necessities Calculate values.

Another development of the method according to the invention stipulates that the critical time window over timing information of the modules (transmitter, receiver) and of the digital network. For example, the critical time window in the case of synchronous signals by the relative timing of the signal clock to the transmitter, the relative timing of the signal clock to the receiver, the Duration of the signal on the line and the setup and hold times of the receiving module.

In addition, the inventors beat before, a process for unbundling digital networks, using digital Components and conductor tracks on at least one circuit board, wherein at least between creating a circuit and unbundling a crosstalk limit is determined to further develop that the for each digital network electrically necessary crosstalk limit, according to a the configurations described above, preferably automatically, is determined.

This ensures that the arrangement of the digital components and traces on the circuit board with respect to each other Distance can be optimized and thus complex systems can be realized can.

It goes without saying that the above-mentioned methods are carried out with the aid of a computer program and stored as a computer program on at least one computer-readable data carrier can be.

Other design options result from the claims.

The invention is explained below of a preferred embodiment with the help of the figures described. Show it:

1 : Scheme for determining the crosstalk limit values based on technology-dependent static signal-to-noise ratios;

2 : Simulated voltage curve at the receiver input of a digital network;

3 : Voltage scheme to clarify the determination of the crosstalk limit values according to the invention;

4 : Scheme for the inventive determination of the physically necessary crosstalk limit values.

The 1 shows a diagram which clarifies the determination of the crosstalk limit values, according to the prior art, with the aid of technology-dependent static DC signal-to-noise ratios.

For this, a classification of all Modules of the digital network carried out using a network list. For every class of the blocks (TTL, CMOS, etc.), certain static DC voltage to noise ratios (DC to noise ratios) are defined. These DC signal-to-noise ratios can be used Example from application manuals be read. The determination takes place manually.

However, because of this DC to noise ratios are determined conservatively, are also very conservative and network class-dependent Assign crosstalk limits.

The 2 shows a simulated voltage curve U_in at the receiver input of a digital network.

The time axis t of the voltage curve U_in is divided into a large number of areas, the time areas, in which crosstalk can lead to data corruption, as a critical time window Δt_krit_0 to Δt_krit_2 are marked. The recipient is only during this critical time window Δt_krit_0 to Δt_krit_2 in a detection state while the other time he is in a waiting state. So in the waiting state lead state changes at the block input not to change the internal logic state of the building block.

To calculate the crosstalk limits is within the critical time window Δt_krit_1 that the simulated Voltage curve of a low state of the transmitter contains one maximum low voltage U_in_low_max of the voltage curve U_in determined. The maximum value of the voltage curve U_in, within the critical Time window Δt_krit_1, therefore represents the maximum low voltage U_in_low max.

Likewise, within the other critical time window Δt_krit_2, that contains the simulated voltage curve of a high state of the transmitter, one Minimum high voltage U_in_high_min of the voltage curve U_in determined by using the minimum value.

For example, the receiver recognizes a high state of the transmitter is not when within the critical Time window Δt_krit_2 the one occurring at the recipient minimum voltage U_in_high_min below a switching threshold U_threshold of the recipient decreased becomes. This range between U_threshold and U_in_high_min respectively between U_threshold and U_in_low_max, thus provides a "reserve" for the line in the Grid coupled in and tolerable interference voltages.

The 3 shows a voltage diagram that illustrates the composition of the interference voltage coupled into the digital network.

This coupled interference voltage essentially has three parts, supply voltage fluctuations (Simultaneous Switching Noise, SSN) on the transmitter ΔU_SSN_trans, supply voltage fluctuations at the receiver ΔU_SSN_rec and cross talk voltages.

Supply voltage fluctuations on the transmitter ΔU_SSN_trans and at the receiver ΔU_SSN_rec can for example by simultaneously switching drivers on the same block dips occur on the assembly, etc.

The supply voltage fluctuations on Transmitter ΔU_SSN_trans lower the minimum high voltage U-in_high_min and increase the maximum low voltage U_in_low_max of the transmitter by the amount ΔU_SSN_trans.

It is also used to calculate the crosstalk thresholds note that the Switching threshold U_threshold of the receiver has a tolerance range, with a minimum limit U_threshold_min and a maximum Limit U_threshold_max.

The supply voltage fluctuations on Receiver ΔU_SSN_rec now lower this minimum limit value U_threshold_min and increase the maximum limit value U_threshold_max by the amount ΔU_SSN_rec.

Remains as a hatched area the "reserve" of the line for permissible crosstalk. Received in the high state of the transmitter thus the crosstalk limit value ΔU_xtalk_high and in the low state of the transmitter the crosstalk limit value ΔU_xtalk_low.

If the crosstalk voltages U_xtalk that occur are smaller than the shaded area, no malfunctions of the circuit are to be expected. The permissible crosstalk voltages U_xtalk result from the following equation: –Min (ΔU_xtalk_low, ΔU_xtalk_high) <U_xtalk <min (ΔU_xtalk_low, ΔU_xtalk_high)

The crosstalk limit value ΔU_xtalk_high in the high state of the transmitter can be determined using equation (1), the crosstalk limit value ΔU_xtalk_low in the low state of the transmitter can be determined using equation (2): ΔU_xtalk_high = U_in_high_min - | ΔU_SSN_trans | - | ΔU_SSN_rec | - U_threshold_max (1) ΔU_xtalk_low = U_threshold_min - | ΔU_SSN_trans | - | ΔU_SSN_rec | - U_in_low_max (2)

To simplify the unbundling of an assembly, an absolute amount ΔU_xtalk can be specified for the permissible cross-talk voltages U_xtalk. This crosstalk limit value ΔU_xtalk is the minimum of the crosstalk limit value ΔU_xtalk_high in the high state and the crosstalk limit value ΔU_xtalk_low in the low state of the transmitter: | U_xtalk | <ΔU_xtalk = min (ΔU_xtalk_high, ΔU_xtalk_low) (3)

The 4 shows a scheme for the inventive determination of the physically permissible crosstalk limit values.

The limit values ΔU_xtalk_low and ΔU_xtalk_high for the permissible Crosstalk in the low or high state of the transmitter are therefore also With the help of a simulation of the individual networks with the connected ones digital transmitters and receivers certainly.

For the simulation will be the following input data in electronic form to disposal provided: the network list, models of the modules used (module models), Information about the physical Network properties, such as line impedance and layer structure, network topology and network length, as well as timing information.

• – das Verhalten der Sender und Empfänger, beispielsweise deren Versorgungsspannungsschwankungen ΔU_SSN_trans und ΔU_SSN_rec, (wenn diese Daten nicht vorhanden sind, dann müssen sie aus den Gehäusedaten, Aufbau des internen Versorgungssystems und der maximalen Anzahl der gleichzeitig schaltenden Buffer berechnet werden)
• – die Schaltschwelle U_threshold des Empfängers, sowie die Grenzwerte der Schaltschwelle U_threshold_max und U_threshold_min,
• – Setup- und Holdzeiten, die für die Ermittlung der kritischen Zeitfenster Δt_krit_X benötigt werden,
• – Aufbau des internen Spannungsversorgungssystems, Gehäuseeigenschaften, etc. die einen Beitrag zur Simulation des Spannungsverlaufs U_in liefern.

The building block models can provide information about

• - The behavior of the transmitter and receiver, for example their supply voltage fluctuations ΔU_SSN_trans and ΔU_SSN_rec, (if this data is not available, then they have to be removed from the housing the structure of the internal supply system and the maximum number of simultaneously switching buffers)
• The switching threshold U_threshold of the receiver, and the limit values of the switching threshold U_threshold_max and U_threshold_min,
• - Setup and hold times that are required to determine the critical time window Δt_krit_X,
• - Structure of the internal voltage supply system, housing properties, etc., which contribute to the simulation of the voltage curve U_in.

To simulate the voltage curve U_in be over it also information from the network list and the network topologies as well of the layer structure.

From the timing information of the blocks and the critical time window of the system is determined.

Furthermore, those for the calculation who needed crosstalk limits minimum high voltage U_in_high_min and the maximum low voltage U_in_low_max from the simulated voltage curve U_in and the critical one Time window Δt_krit determined.

All entries are in electronic Form available Then the simulation can be largely automated before starting the assembly unbundling take place.

It is understood that the above mentioned features of the invention not only in the specified Combination, but also in other combinations or alone can be used without departing from the scope of the invention.

In summary, a tension curve simulates a minimal high voltage within critical time windows and determined a maximum low voltage and from there, with the help the supply voltage fluctuations of the transmitter and the receiver and the thresholds of the switching threshold of the receiver, at least one crosstalk threshold calculated. This is the manual assignment of conservative, network class-dependent No crosstalk limits. This leads to higher Limit values and thus more freedom in component unbundling.

Claims (10)

Method for determining at least one crosstalk limit value (ΔU_xtalk) of a crosstalk voltage (U_xtalk) from digital networks which have at least one digital transmitter with a high and a low state, and at least one digital receiver with a switching threshold (U_threshold) which has a maximum Has limit value (U_threshold_max) and a minimum limit value (U_threshold_min), whereby interference voltages are coupled into the digital networks, which largely consist of supply voltage fluctuations (ΔU_SSN_trans) at the transmitter, supply voltage fluctuations at the receiver (ΔU_SSN_rec) and the crosstalk voltage, characterized in that that - a voltage curve (U_in) at the receiver is simulated during the transmission of digital signals between the transmitter and the receiver, - a time axis of the voltage curve is divided into a large number of areas which alternate a detection state (critical time window (Δt _krit_X)) and describe a waiting state of the receiver, - the low state of the transmitter is simulated within at least one critical time window (Δt_krit_1) and a maximum low voltage (U_in_low max) of the voltage curve (U_in) is determined, - within at least one other critical time window (Δt_krit_2) the high state of the transmitter is simulated and a minimum high voltage (U_in_high_min) of the voltage curve (U_in) is determined, and - from the minimum high voltage (U_in_high_min), the supply voltage fluctuations at the transmitter (ΔU_SSN_trans ) and at the receiver (ΔU_SSN_rec) and the maximum limit value of the switching threshold (U_threshold_max) and / or from the maximum low voltage (U_in_low_max), the minimum limit value of the switching threshold of the receiver (U_threshold_min) and the supply voltage fluctuations at the transmitter (ΔU_SSN_trans) and at the receiver (ΔU_SSN_rec) the crosstalk limit (ΔU_xtalk) is calculated. Method according to the preceding claim 1, characterized in that for estimating the permissible crosstalk limit value (ΔU_xtalk), in the high state of the transmitter, a crosstalk limit value (ΔU_xtalk_high) is calculated by the amounts of the supply voltage fluctuations from the minimum high voltage (U_in_high_min) The transmitter (ΔU_SSN_trans) and the receiver (ΔU_SSN_rec) as well as the maximum limit of the switching threshold (U_threshold_max) are subtracted after: ΔU_xtalk_high = U_in_high_min - | ΔU_SSN_trans | - | ΔU_SSN_rec | - U_threshold_max. (1) Method according to one of the preceding claims 1 to 2, characterized in that to estimate the permissible crosstalk limit value (ΔU_xtalk), in the low state of the transmitter, a crosstalk limit value (ΔU_xtalk_low) is calculated by the amounts from the minimum limit value of the switching threshold (U_threshold_min) the supply voltage fluctuations at the transmitter (ΔU_SSN_trans) and at the receiver (ΔU_SSN_rec) as well as the maximum low voltage (U_in_low_max) are subtracted after: ΔU_xtalk_low = U_threshold_min - | ΔU_SSN_trans | - | ΔU_SSN_rec | - U_in_low_max. (2) Method according to one of the preceding claims 2 to 3, characterized in that the permissible crosstalk voltage (U_xtalk) is determined from the minimum of the crosstalk limit value (ΔU_xtalk_low) in the low state of the transmitter and the crosstalk limit value (ΔU_xtalk_high) in the high state of the transmitter according to: | U_xtalk | <min (ΔU_xtalk_low, ΔU_xtalk_high). (3) Procedure according to a of the preceding claims 1 to 4, characterized in that the size of the supply voltage fluctuations on the transmitter (ΔU_SSN_trans) and at the receiver (ΔU_SSN_rec) from an estimate is obtained. Procedure according to a of the preceding claims 1 to 5, characterized in that the size of the supply voltage fluctuations on the transmitter (ΔU_SSN_trans) and at the recipient (ΔU_SSN_rec) is obtained from a simulation. Procedure according to a of the preceding claims 1 to 6, characterized in that the critical time window (Δt_krit_X) over a Timing information of the blocks and the digital network determined become. Procedure for unbundling digital networks, with digital components and conductor tracks, on at least one circuit board, with at least one between creating a circuit and unbundling Crosstalk limit (ΔU_xtalk) is determined, characterized in that the electrical for each digital network necessary crosstalk limit (ΔU_xtalk), according to one the preceding claims, preferably automatically. Computer program product with program code means, by at least all the steps according to at least one of the preceding claims 1 to 8, if the program code means are executed on a computer. disk with a computer program with program code means to at least all steps according to at least one of the preceding claims 1 to 8, if the program code means are executed on a computer.