Method and circuit arrangement for adjusting the neutral setting of a demodulator

(42) Date of commencement of the patent: 15. 7.1990 (45) Date of issue: 11. 2.1991 (30) Priority:

19th 5.1984 DE 3418702 claimed. (56) citations;

(73) Patent owner:

CABLE METAL ELECTRO COMPANY WITH LIMITED LIABILITY

D-3000 HANNOVER (DE).

DE-PS2141198 DE-PS2456664 US-PS 4039751 US-PS 4034340 US-PS 3962637

AKASHI, FUMIO, TATSUI, NORITAKA, SATO YOICHI, KQIKE, SHIN-ICHI, MARUMO, YASUSHI: "A HIGH PERFORMANCE DIGITAL QAM 9600 BIT / S MODEM", NEC RESEARCH AND DEVELOPMENT, NO. 45, APRIL 1977, pp 38-48 STROH, RAYMOND W .: "AN EXPERIMENTAL MICROPROCESSORIMPLEMENTED 4800 BIT / S LIMITED DISTANCE VOICE BAND PSK MODEM", IEEE TRANSACTIONS ON COMMUNICATIONS,

VOL. COM-26, NO. 5, MAY 1978, p. 507-512 (54) METHOD OF TRANSMITTING DATA (57) A method for balancing demodulators (4) is provided, which together with a microprocessor (2) and a modulator (3) are arranged in a data transmission device (1). The digital transmission data sent from the microprocessor (2) to the modulator (3), after being recovered by the demodulator (4), is fed back to the microprocessor (2) as digital receive data and compared with the transmitted data. Modulator (3) and demodulator (4) are connected by means of a switch (7). In the event of a deviation from transmission data and reception data, the demodulator (4) is adjusted by the microprocessor (2) in the direction of equalization.

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CQ

AT 392 178

DZR 0073013

AT 392 178 B

The invention relates to a method for transmitting data over a transmission path by means of a device in which a modem consisting of modulator and demodulator is arranged, with which before the actual operating phase first digital transmission data with predetermined bit pattern generated and transferred in the modulator in analog data with which the analog data within the device the

Demodulator be supplied and with which the demodulator leaving digital receive data are compared with the transmission data. Such a method is known from DE-PS 2141198.

In general, the invention relates to data transmission by means of analog transmission methods. In particular, it relates to the field of communications engineering. It should be irrelevant whether the data is transmitted wirelessly or via metallic conductors or via optical fibers. In known technique to do so

Data transmission equipment used to convert an incoming digital data stream into an analogue l

Convert data stream, which is transferred after replacing the transmission line back into a digital data stream.

For the conversion of the data streams so-called modulator and demodulator modems are used. These are components that can be used, for example, by frequency shift keying or

Phase shift keying convert digital signals to analog signals and vice versa. Such modems are used, for example, in telephone traffic and screen text. They are usually coupled with microprocessors. For a faultless transmission of the data and in particular for the recovery of the digital data used in the modem demodulator must be able to properly recognize the incoming analog signal, for which he limits are given. If a binary code is used for the transmission, then the demodulator must be able to recognize two states correctly, for example. For example, in the case of frequency shift keying, these are the two characteristic frequencies which are above or lie below a limit frequency predetermined by the demodulator.

So that the demodulator can fulfill this task and thus a perfect operation of the data transmission device is possible, it must be adjusted to achieve a neutral position. The time and personnel costs for this is high in the currently known procedure, because for adjusting a balancing operated, read a meter and at least one resistor must be soldered. After adjustment, the neutral position of the demodulator is fixed once and for all, and it is operated with this setting over its entire life. Aging processes and other influences are no longer considered

From US-PS 4,034,340 a circuit for determining the quality of incoming digital data in a receiver is known. The data is fed to a decision network via a demodulator and a low-pass filter. This network is controlled during the current data transmission in such a way that sampling is always carried out at the optimum time.

The method according to the aforementioned DE-PS 2141198 relates to a loop measurement in modems for

Two wire businesses. The patent mentions that for this purpose a modem can be sprayed separately by connecting the output of the transmitting device to the input of the receiving device after the modem.

The invention has for its object to provide a method by which an automatic adjustment of the neutral position of a demodulator can be achieved.

The object is achieved by a method of the type described according to the invention characterized in that a deviation signal is generated from the deviation of the bit patterns of transmission data and reception data from a microprocessor, that the demodulator is adjusted to compensate for its neutral position by the adjustment signal generated by the microprocessor in the sense of compensation and that the adjustment signal is stored in the memory of the microprocessor and used for the further operation of the transmission path.

This method offers the advantage that those used in a data transmission device

Demodulatoren no longer need to be adjusted by hand. The time and personnel required so far for reconciliation is falling. The adjustment of the demodulators now takes place in a running in a short time of about 0.5 to 1.0 s test procedure after switching on the supply voltage of the data transmission device, but before the actual operating phase. Under operating phase is in the case of a dedicated line, the data transfer itself to understand, while they are without dedicated line

Construction process of the transmission path with subsequent data transmission means

It is particularly advantageous that the adjustment process can be performed each time when the supply voltage is turned on, so that the adjustment of the neutral position of the demodulators is always performed again. Aging and other influences are constantly taken into account.

The digital transmission data with the predetermined bit pattern are advantageously generated by the microprocessor.

It can then be dispensed with an additional device for generating the transmission data.

The microprocessor advantageously generates as transmit data a bit pattern which has a duty ratio of 1: 1.

The time length of the O-bits and the 1-bits is then the same and the adjustment process can be made as short in time as possible.

Advantageously, the adjustment signal is generated as a pulse width modulated signal, which before its delivery to the

Demodulator is integrated. In this way, the adjustment signal can be generated with particularly few and simple components.

According to a proposal of the invention it is provided that the adjustment signal integrated by an RC element

-2AT392178B and the demodulator is supplied. Since an RC element containing only passive elements is used for the integration, this can be very simple.

The method according to the invention will be explained with reference to the circuit diagram shown in the drawing as an exemplary embodiment.

The dotted line schematically indicates a data transmission device (DÜE) (1). The DÜE (1) comprises a microprocessor (2), a modulator (3) and a demodulator (4). It is supplied from a current source indicated by the arrow (5). Modulator (3) and demodulator (4) can be combined to form a dashed bordered modem (13). Between microprocessor (2) and demodulator (4) also a simply constructed integrator is turned on, which consists for example of a RCGlied (6).

The method according to the invention operates, for example, as follows:

After switching on the supply voltage, the DÜE (1) by a signal of the microprocessor (2) is first separated from the data transmission path. For this purpose, the switch (7) is actuated, which is brought into its dashed line position in which it connects the modulator (3) with the demodulator (4). This connection can be made directly or via an attenuator as shown. The data transmission path is indicated by a transmission path (8) and a reception path (9), which are not connected to the DÜE (1) during the adjustment process. Both paths can be wireless. They can consist of metallic conductors or optical waveguides.

When the change-over switch (7) is placed in its dashed position, the microprocessor (2) sends transmission data of a predetermined bit pattern generated by it via the path (10) to the modulator (3), which converts the digital data into analog data. The analog data passes to the demodulator (4) and is fed back from it as recovered digital receive data via the path (11) to the microprocessor (2). The microprocessor (2) now compares the bit patterns of transmit and receive data. In the event of a deviation, an adjustment signal is sent via the path (12) to the demodulator (4), which is converted in the integrator into a DC voltage, for example. The calibration process takes about 0.5 to 1.0 s. After the adjustment, the changeover switch (7) is returned to its position shown in the drawing, in which the transmission paths (8) and (9) to the DÜE (1) are connected. The actual operation phase of the DÜE (1) can now begin.

For the adjustment process, the microprocessor (2) generates a bit pattern with the duty cycle 1: 1 at a corresponding transmission rate for the transmission data. As a balancing signal between microprocessor (2) and demodulator (4), a pulse width modulated signal can be used, which adjusts a DC voltage after integration in the simple integrator at the demodulator (4). This adjustment ensures that the bit patterns of transmit data and receive data are the same. The demodulator (4) is aligned with it. The pulse ratio of the pulse width modulated signal used for the adjustment of the demodulator (4) is known to the microprocessor (2). It is stored as a parameter in the memory of the microprocessor (2) and used for further operation of the data transmission path.

For the sake of completeness it should be noted that the adjustment process according to the invention can in principle be carried out in each case after switching on the supply voltage. With short intervals between switching the supply voltage off and on again, the adjustment is not always necessary. If the supply voltage is present for a very long time, the adjustment can also be carried out in between, for example during transmission pauses.