DE102006062598B4 - ASK demodulator - Google Patents

Abstract

A demodulator (1) for demodulating ASK signals, comprising:
a signal input (2) to which a carrier with modulated ASK signal is applied,
a symmetrical envelope demodulator (3) which demodulates a data signal from a carrier frequency, the envelope detector (3) for a positive branch and a negative branch each having an input diode (31, 32) to which the signal to be demodulated from a signal input (2) is simultaneously supplied to simultaneously demodulate the positive and the negative half-wave of the signal;
a DC decoupler (4), the DC decoupler decoupling respectively the DC component of the output signal on the positive branch and the negative branch of the envelope demodulator;
a potential conditioner (5) connected downstream of the DC decoupler (4) for adjusting the potentials of the signals of the negative and positive branches to be supplied as a difference signal to a comparator (6), the potential conditioner (5) each having a voltage divider (51, 52) for the positive branch and the negative branch, wherein the voltage divider are each connected between the operating voltage UB and ground (20);
a comparator (6) whose output (63) is switched only in response to the difference between the matched signals of the positive and the branch and which outputs a demodulated signal; and
wherein the positive and the negative branch have a mutually symmetrical structure.

Description

The present invention relates to a demodulator for amplitude modulated signals, in particular for the demodulation of amplitude shift keying signals (ASK). ASK is a digital modulation type wherein the amplitude of a carrier signal for information transmission is changed. ASK generally includes non-return-to-zero (NRZ) signals that do not fall back to zero potential at regular intervals. An NRZ signal contains only the pure binary coded user data, where zero and one bits are often represented by positive and negative potential.

Such forms of data transmission are suitable for example for inductively coupling connector couplings, as sold by the applicant under the name Memosens.

For example, in the prior art, data sent by ASK is demodulated with an envelope demodulator, but since the NRZ-encoded data signal has a DC component, the level of the thus recovered signal varies considerably.

So that the comparator threshold can be adapted to the fluctuations, a clamping circuit is used. The circuit provides by means of diodes via a coupling of the voltage paths of data signal and comparator threshold to the operating voltage for a mutual compensation of the fluctuations. When the signal voltage increases, the comparator threshold also rises. Thus, the disturbances in the signal recovery can be minimized. However, the circuit described has the following disadvantages: The clamping circuit is temperature-dependent due to the Schottky diodes used there. Furthermore, the circuit is comparatively sluggish, so that the comparator threshold can not be tracked fast enough. Thus, fast disturbances in the data signal, for example in the middle μs range, can not be intercepted. Furthermore, a high degree of modulation is required, which allows only a narrow range of variation. In addition, the demodulator and the signal recovery are load-dependent. Finally, disturbances emanating from the operating voltage affect differently on the two voltage paths, ie data signal and comparator threshold.

The US 2006/0103457 A1 FIG. 12 shows a system and method for demodulating RF-amplified modulated signals by means of a positive branch envelope detector and a negative branch envelope detector. Envelope detectors use NMOS and PMOS transistors, respectively.

The GB 2 078 034 A shows a phase separation indicator for audio signals by means of oppositely connected diodes for providing 180 ° out of phase audio signals for operating a push-pull output stage of class AB for a radio receiver.

The FR 2 415 388 A1 shows a control circuit for an alternating current, which is pulse-modulated with characteristic information representing the integrity of a conveyor belt or similar device.

The EP 1 251 458 A2 shows a semiconductor integrated circuit and a non-contact information medium such as a chip card with this semiconductor circuit. The circuit includes a demodulator for demodulating received input signals to replicate data.

The US Pat. No. 3,514,720 shows a balanced modulator-demodulator circuit for amplitude modulation and demodulation for phase-coherent AC signals with suppression of the carrier signal.

The US 2006/0199560 A1 shows a system for distance measurement in which a RF communication signal is generated by an external device, wherein the communication signal is symmetrically coded with respect to the DC component before the transmission to improve the robustness of the wireless signal.

It is the object of the present invention to provide a demodulator which overcomes the described disadvantages of the prior art.

The object is achieved by the demodulator according to independent claim 1.

The demodulator according to the invention for demodulating ASK signals comprises
a signal input to which a carrier with modulated ASK signal is applied,
a symmetric envelope demodulator which demodulates a data signal from a carrier frequency, the positive and negative branch envelope demodulator each comprising an input diode to which the signal to be demodulated is simultaneously applied to simultaneously clamp the positive and negative half-waves of the signal to demodulate;
a DC decoupler, the DC decoupler decoupling respectively the DC component of the output signal on the positive branch and the negative branch of the envelope demodulator;
a potential conditioner connected downstream of the DC decoupler for adjusting the potentials of the negative and positive branch signals to be supplied as a difference signal to a comparator, the potential conditioner each comprising a voltage divider for the positive branch and the negative branch; Voltage divider are each connected between the operating voltage UB and ground; and
a comparator whose output is switched only in response to the difference between the matched signals of the positive and the branch and which outputs a demodulated signal; and
wherein the positive and the negative branch have a mutually symmetrical structure.

In one embodiment of the invention, the DC decoupler for the positive branch and the negative branch each comprise a longitudinal capacitor.

In one development of the invention, the comparator comprises an operational amplifier, at the input of which the conditioned signals of the positive and negative branches are present.

Compared with the prior art, the demodulator circuit according to the invention has the advantage that disturbances, for example the operating voltage or the amplitude of the carrier signal, have the same effect on both signal paths due to the largely symmetrical structure and are thus compensated.

Likewise, the fluctuating DC component of the data signal acts on both circuit branches, eliminating its interfering influence on the demodulation.

The use of the two half-waves of the carrier signal also allows a safe demodulation even at low modulation strokes.

Finally, the comparator requires no further wiring due to the exclusive dependence on the conditioned difference signal.

The invention will now be explained with reference to an embodiment shown in the drawing.

• 1: einen schematischen Schaltplan eines Ausführungsbeispiels einer erfindungsgemäßen Demodulatorschaltung.

It shows:

• 1 : A schematic circuit diagram of an embodiment of a demodulator circuit according to the invention.

In the 1 illustrated demodulator circuit 1 includes the signal flow described in the following components: A signal input 2 to which a carrier with modulated ASK signal is applied, a balanced envelope detector 3, a DC decoupler 4 , a potential conditioner 5, and a comparator 6 which outputs a demodulated signal.

Basically, the circuit components mentioned after the signal input 2, which will now be described in more detail, substantially symmetrical with respect to a ground branch 20 designed to include a positive branch and a negative branch.

The envelope demodulator 3 includes one input diode each for the positive and negative branches 31 . 32 whereby the sign of the branch is fixed. This is followed in each case by a capacitor 33, 34 in both branches and a resistor in parallel thereto 35 . 36 , wherein the capacitor and the resistor are connected across the signal path to the ground branch.

The DC decoupler 4 comprises in each case a longitudinal capacitor in the positive branch and in the negative branch 41 . 42 in the signal path, eliminating the DC components in both branches.

The potential conditioner 5 , comprises in the positive branch and in the negative branch each transverse to the signal path a voltage divider 51 . 52 the between mass 20 and + UB is switched across the signal path. Parallel to the voltage dividers is a capacitor 53 . 54 intended.

The components, ie diodes, resistors and capacitors, are dimensioned so that the information to be used at the input 2 pending modulated ASK signal is completely contained in the difference of the conditioned signals at the positive and the negative branch.

The comparator 6 includes an operational amplifier 60 , at whose inputs 61, 62 the conditioned signals of the positive and the negative branch are present. The output of the operational amplifier 23 is switched according to the signal difference between its inputs.

Claims (3)

A demodulator (1) for demodulating ASK signals, comprising: a signal input (2) to which a carrier with modulated ASK signal is applied, a balanced envelope demodulator (3) which demodulates a data signal from a carrier frequency, the envelope demodulator (3 ) comprises in each case an input diode (31, 32) for a positive branch and a negative branch, to which the signal to be demodulated from a signal input (2) is simultaneously supplied to simultaneously demodulate the positive and the negative half-wave of the signal; a DC decoupler (4), the DC decoupler decoupling respectively the DC component of the output signal on the positive branch and the negative branch of the envelope demodulator; a potential conditioner (5) connected downstream of the DC decoupler (4) for adjusting the potentials of the signals of the negative and positive branches to be supplied as a difference signal to a comparator (6), the potential conditioner (5) each having a voltage divider (51, 52) for the positive branch and the negative branch, wherein the voltage divider are each connected between the operating voltage UB and ground (20); a comparator (6) whose output (63) is switched only in response to the difference between the matched signals of the positive and the branch and which outputs a demodulated signal; and wherein the positive and the negative branch have a mutually symmetrical structure. Demodulator after Claim 1 wherein the DC decoupler (4) for the positive branch and the negative branch each having a longitudinal capacitor (41, 42). Demodulator after Claim 1 or 2 wherein the comparator (6) comprises an operational amplifier (60) at whose inputs (61, 62) the conditioned signals of the positive and negative branches are applied.

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