DE4026878A1 - Digital transmitter module pref. for MSK signal shaping - incorporates selected frequency registers and multiplexers feeding digital synthesiser for free choice of frequency shift - Google Patents

Abstract

The min. shift keyed signal is produced directly in the passband from the desired frequencies stored in two registers (31,32) between loading and control input multiplexers (21,22). The output (12) is taken from a digital frequency synthesiser (30) which guarantees phase continuity. With constant replenishment of the registers (31,32) a quasi-continuous and esp. linear frequency modulation (chirp) is possible. A separate input (15) is provided for local control (33). CW output is obtainable with constant input (11). USE/ADVANTAGE - E.g. in secret communication and radar systems. Programmable module can be integrated monolithically for reliability and economy of material.

Description

The invention relates to a transmitter module according to the Oberbe handle of claim 1.

The invention of the type mentioned u. a. in fault / down Hearing-safe devices and radars are used and therefore comes z. B. in the field of news / signal wear to application.

The invention has for its object a fully digital The programmable transmitter module for low-cost Synthesis of spread spectrum waveforms, preferably for Implement MSK waveforms. (MSK = minimum shift Keying). This module should be monolithically integrable  and therefore reliable, inexpensive, material-saving and turn out to be easy to manufacture.

The achievement of the object is in Pa Claim 1 described. In the subclaims are advantageous training and further education and preferred to uses of the invention listed.

The achievement of the object is that the MSK signal directly digital in the bandpass range by pre the two frequency values stored in two registers and continuous switching in frequency synthe sizer, also called frequency generator. By suitable selection of the register contents are at the exit of the Any frequency-modulated signals, such as B. FSK, chirp signal, can be generated.

In particular, the frequency generator delivers by default of a single constant frequency value an unmodulated t carrier signal.

The aforementioned bandpass signals can optionally be one Phase shift modulation (PSK) are subjected.

The present arrangement according to the invention is reliable sig, inexpensive, material-saving and easy to manufacture and fulfills the task in full.

The invention is based on Fig. 1 and explained in Fig. 2 in more detail. Show it:

Fig. 1 is a block diagram of an advantageous exporting approximate shape of the inventive arrangement;

Fig. 2 is a block diagram of a Wei invention terbildung the arrangement of FIG. 1.

The inventive arrangement of FIG. 1 has a La deeingang 10, a signal output 12, a control input 11 and a control input 15. The charging input 10 is at a first multiplexer 21 , the control input 11 is at a second multiplexer 22 , the signal output 12 is at a digital frequency synthesizer 30 and the control input 15 at a local controller 33 .

The outputs of the first multiplexer 21 are each switched via a first or second register 31 or 32 to the associated inputs of the second multiplexer 22 . This second multiplexer 22 is connected to the digital frequency synthesizer 30 .

In the further development according to the invention according to FIG. 2, a phase shift key, in the wide ren multiplier 70 , is formed at the signal output 12 according to FIG. 1. This multiplier 70 also has an input 13 and an output 14 .

The desired MSK frequency values are stored in the two registers 31 and 32 . In accordance with the digital message d _f (k) to be transmitted, which is present at the control input 11 , k is the discrete time, the control input 11 of the digital frequency synthesizer 30 (also called frequency synthesizer) is connected to the two registers 31 and 32 , so that the frequency synthesizer 30 generates the desired phase-continuous MSK signal. The phase continuity is ensured by suitable implementation of the frequency synthesizer 30 .

If the control input 11 maintains a constant value, the frequency synthesizer 30 delivers a carrier oscillation of constant frequency (CW signal).

Any FSK can be chosen by freely selecting the frequency values possible.

By constantly reloading the two registers 31 and 32 , quasi-continuous frequency modulation, in particular special time-linear frequency modulation (chirp) is possible.

Here, the frequency synthesizer 30 is preferably integrated monolithically or as a gate array.

Important digital modulation types such as e.g. B. (PN-) MSK, FSK, (PN-) PSK, (PN-) PSK / (PN-) FSK, Chirp, Chirp / (PN-) PSK, frequency hopping (= pseudorandom FSK with more than two different frequencies), (PN-) PSK / frequency hopping directly digital in the bandpass range produce.

The multiplier 70 of FIG. 2 is inverted in accordance with the control signal d _p (k) at the input 13 the output signal of the synthesizer 30, and thus realizes the PSK at from passage 14. The transmitter module is preferably integrated monolithically, and possibly formed as a gate array.

The digital output signals of the frequency synthesizer 30 or the transmitter module can be further processing, z. B. for analog implementation in the transmission frequency range, implemented in the analog range. This is conveniently done with an external Digi tal / analog converter.

Functional relationships (rules) are particularly advantageous for MSK synthesis are the following.

The frequency synthesizer 30 used is characterized by

Frequency increment: Δf (1.1)
minimum frequency: f _min = Δf (1.2)

maximum frequency: f _max = NΔf (1.3)
N∈ N {0}, N »1

The maximum synthesizer frequency is so defi in the following niert that taking into account the sampling frequency of Frequency synthesizers the sampling theorem is just fulfilled. However, the maximum synthesizer frequency can also be significant be chosen lower.

The minimum distance

Δf _MSK = f⁺-f ^- (2.1)

the upper f and lower f MSK frequency is therefore the same the frequency increment Δf. This frequency separation

Δf _MSK = f _c / 2 (2.2)

is equal to half the chip frequency f _c or equal to half the bit frequency. The possible chip frequency values result from this

f _c = k2Δf, k∈ N {0}, (2.3)

as an integer multiple of the double synthesizer fre quota increments.

The bandwidth of an MSK waveform between the first Is zeroing

B≈1.5f _c (3)

equal to approximately 1.5 times the chip frequency. Under Be consideration of the sampling theorem applies

B <f _max (4)

ahead of the maximum allowable chip frequency

f _{c, max} ≈2f _max / 3 (5)

follows in about 2/3 of the maximum synthesizer frequency and the MSK center frequency is equal to half the maximum synthesis sizer frequency is.

The bandwidth of an MSK signal is the one within about 99% of the total signal energy is available, the maximum permissible chip frequency is approximate assign

f _{c, max} ≈5f _max / 12. (6)

The MSK center frequency is therefore dependent on the Chip frequency selectable within wide limits. With large values the choice of chip frequency is preferred

MSK center frequency: f _max / 2 (7.1).

Taking into account the sampling theorem, the following roughly applies

lower MSK frequency f ^- : f _max / 3. . . 19f _max / 48 (7.2)

upper MSK frequency f⁺: 29 · f _max / 48. . . 2f _max / 3 (7.3)

maximum chip frequency f _c : f _max / 3. . . 5f _max / 12 (7.4)

If the chip frequency is low, the MSK center fre quenz not the above Obey condition (7.1). It is just make sure that the sampling theorem is satisfied is. The minimum possible chip frequency is.

minimum chip frequency f _c : 2 · Δf. (8th)

Claims (5)

1. Transmitter module, characterized in that a fully digital, programmable transmitter module is designed for the synthesis of spread spectrum signal forms. 2. Arrangement according to claim 1, characterized in that

• - An MSK signal is generated directly digitally in the bandpass range by specifying two frequency values stored in registers ( 1 or 2 ) and phase-continuous switches in the frequency synthesizer;
• - Any suitable frequency-modulated signals are generated by suitable selection of the register contents at the output ( 12 ) of the frequency generator ( 30 ).

3. Arrangement according to claim 1 and / or 2, characterized in that the outputs of a first multiplexer ( 21 ) each via a first or second register ( 31 ) or ( 32 ) on the associated inputs of a second multiplexer ( 22 ) are connected, and that this second multiplexer ( 22 ) is connected to the digital frequency synthesizer ( 30 ). 4. Arrangement according to one of the preceding claims, characterized in that the output ( 12 ) of the digita len frequency synthesizer ( 30 ) is connected to a multiplier ( 31 ). 5. Arrangement according to one of the preceding claims, since characterized in that the bandpass signals choice undergo phase shift modulation (PSK) are.