KR20010083804A - Bio-Signal Modem using the Coherent Amplitude Modulation and Demodulation Method - Google Patents

Abstract

PURPOSE: A bio-signal modem is provided to stably embody multiple channels, and to achieve a great amount of low frequency band signals from a limited frequency band of a sound card. CONSTITUTION: For embodying a signal modem(9) for utilizing a sound card basically contained in the computer as an analog-digital converter, a signal modulation part(26) consists of a reference waveform generator for producing a low frequency band signal and a frequency belonging to an audio band; a signal multiplier for performing the modulation of amplitude by multiplying a reference signal; a band-pass filter part for setting the waveform; and a signal level controller. After the modulation of the attained signal being performed, a modulated signal is applied to one signal line of sound card line-in stereo input lines, and a reference frequency signal is applied to another signal line. Also, for restoring an original signal, a signal demodulation part(6) consists of a low threshold pass filter part.

Description

Bio-Signal Modem using the Coherent Amplitude Modulation and Demodulation Method

The present invention deals with a method of implementing a synchronous amplitude modulation demodulation for a signal modem for utilizing a sound card that is basically built into a computer as an analog to digital converter without a separate analog to digital converter. Analog synchronous amplitude modulation is used to convert low frequency signals to audio frequency signals, and synchronous digital AM demodulation technology is used to restore the discrete signals from the sound card to the original signals.

It also uses frequency division to obtain multiple channel signals for limited sound card inputs. After assigning and applying different frequencies to each channel, a single frequency assigned to each channel is extracted from the discretized stereo signal of the sound card using a bandpass filter and then synchronously demodulated to realize multiple channels.

The present invention is more stable in implementing a signal modem for utilizing a sound card, which is basically built into a computer, as an analog-to-digital converter without a separate analog-to-digital converter, and realizes multiple channels more stably than in a limited frequency band of a sound card. It is designed to increase the multiplexing density so that many low-frequency signals can be obtained. For this purpose, it adopts synchronous amplitude modulation and demodulation method to be possible in sound card environment.

1 is a block diagram of a single channel signal modem according to the present invention.

2 is a schematic diagram of a biosignal modem for utilizing a sound card as an analog-to-digital converter;

3 is a block diagram of a signal converter of a multi-channel system

4 is a block diagram of a signal demodulator in a multichannel system

<Explanation of symbols for main parts of drawing>

5: sound card 6: digital signal demodulator

9: Biosignal modem 13: Line-in stereo terminal

13-1: Left (right) signal terminal of line-in stereo terminal

13-2: Right (left) signal terminal of line-in stereo terminal

18: Stereo signal input to sound card

18-1: Left (right) signal line among stereo input lines

18-2: Right (left) signal line of stereo input line

21: Discrete stereo digital signal from sound card

21-1: Left (right) of discretized stereo digital signals from sound card

21-2: Right (left) of stereo digital signals discretized by sound card

22: Original signal restored through demodulation

26: signal modulator of the signal modem

40: Multiply waveform with amplitude modulation

41: Bandpass filter inserted to shape an amplitude modulated waveform.

42: Gain-variable amplifier for scaling amplitude-modulated signals to ensure smooth input into a sound card

43: Frequency generator for moving signals in the low frequency band to the sound card passband frequency domain

44-1: Arithmetic synthesizer for each channel signal used to carry multichannel signals on one signal line

44-2: Arithmetic synthesizer for each channel reference signal used to carry a multichannel signal on one signal line

50: digital band pass filter 52: digital low pass filter

55: Multiply operator of digital signal

A functional diagram of a biosignal converter configured for acquiring a biosignal from a computer utilizing a sound card as an analog-to-digital converter is shown in FIG. 2. In the present invention, a configuration of the signal modulator 26 and a functional implementation method of the signal demodulator 6 are described. A synchronous amplitude modulation and demodulation method configured for a single channel biosignal is shown in FIG. Figure 1 can be seen that largely composed of three parts. The signal modulator 26, a) and the sound card 5 Finally, the signal demodulator 6, b. The signal input to the signal modulator 26 is an original signal of low frequency detail, and the output signal is an analog signal 18-1 synchronously modulated with a reference frequency waveform and an analog reference signal 18-2 for synchronous modulation. The signal modulator is composed of four parts. A reference frequency (frequency in a sound card band) generator 43, an amplitude modulator 40 that multiplies the signal with the input original signal, and a band pass filter for removing harmonic components that will be included in the reference signal or the original signal, Finally, it consists of a gain control amplifier that modulates the modulated signal to match the sound card's input signal.

The two output signals of the signal converter are connected to the signal lines 13-1 and 13-2 of the sound card line-in stereo terminal 13 and input to the sound card. One of them is an amplitude modulated signal 18-1 and the other is its reference frequency signal 18-2. The sound card discretizes each signal (21). The discretized signal is processed by the signal demodulator 6 to restore the original signal (22). The signal demodulator 6 includes a band pass filter 50 for unifying the reference frequency signal, a multiplication operator 55 for multiplying the signal with the digital signal 21-1, and the original signal 22 in the calculated signal. It consists of a low pass filter 52 for extracting. One of the discretized stereo signals is a reference frequency signal 21-2, and the other is a modulated signal 21-1. A band pass filter 50 is applied to the reference signal to unify its frequency component, and then the signal is multiplied by the modulated digital signal 21-1 (55), and then completely restored to the original signal by passing through the low pass filter. .

As a result, the signal applied to the signal modem was an analog signal in the low frequency band, but after this process, it was discretized in the sound card and converted into a digital signal in the low frequency band in the computer. Modulation and demodulation configured in this way has the advantage that the demodulator can accurately restore the original signal because the reference frequency also changes even if the reference frequency used varies due to various factors. In addition, since the input source signal can have both negative and positive signs, it has a feature that a signal dynamic range can be secured twice that of the asynchronous modulation and demodulation method.

3 and 4 show an implementation of a modulation and demodulation scheme for independent multichannel input signals. The multi-channel input signal is also basically modulated in the manner of FIG. At this time, even if the multi-channel signal is applied to a single signal line, the reference frequency is set differently corresponding to each channel so that each channel can be separated (f1, f2, ... fN). The modulated signal in each channel is then arithmetically summed (44-1) and input to one of the sound card line-in stereo terminals, allowing the sound card to discretize the signal. At the same time, the reference frequency signal used for synchronous modulation is also arithmetic summation of each channel connected to the other input line of the stereo jacks so that the sound card can be discretized.

Discrete signals in a sound card contain two kinds of signals. One is represented by the sum of modulated signals having various reference frequencies (21-1), and the other is represented by the sum of its reference frequency signals (21-2). In Figure 4 it can be seen how to extract the reference signal corresponding to each channel and how to recover the channel signal from the modulated signal sum. The center frequency of each channel's bandpass filter is the reference frequency assigned to the corresponding channel, and the bandwidth is arbitrary, but as the width is reduced, more low-frequency signals can be heard within a given sound card frequency band, resulting in a large number of signals from the computer. Analog-to-digital conversion for use in

The discretized reference signal 21-2 is separated into each channel reference waveform through this band pass filter and multiplies the respective reference frequency signal by the modulated signal 21-1 to act as a low pass filter to produce the original signal of each channel. The signal will be restored. At this time, the interference of other channel signals can be reduced by bringing the cutoff frequency of each channel low pass filter closer to the bandwidth of the channel original signal.

The present invention improves the reliability of the operation and the density of the signal channel multiplexing by implementing a signal modem using a synchronous amplitude modulation demodulation method for utilizing a sound card that is basically built into a computer as an analog-to-digital converter without a separate analog-to-digital converter. In the implementation of synchronous modulation and demodulation, the modulation signal and the modulation reference signal are separately separated using the stereo connection line of the sound card line-in, thereby simplifying the configuration for the function implementation.

Claims (5)

In implementing a signal modem 9 for utilizing a sound card built into a computer as an analog-to-digital converter without an analog-to-digital converter, the signal modulator 26 has a low frequency band having a polarity (+/-) sign. The signal multiplier 40 performs amplitude modulation by the product of the reference signal generated by the reference waveform generator 43, which generates a signal belonging to the audio band and the frequency, and the bandpass filter 41 and the signal size for waveform shaping. And the signal 18-1 is applied to one of the sound card line-in stereo input lines (13-1) and the other signal line (13-2). The reference frequency signal 21-2 is configured by applying the reference frequency signal 18-2, and the signal demodulation unit 6 is a band pass filter 50 of the two stereo signals 21 discretized by the sound card. Via) Then a single frequency component by constructing the modulation signal 21-1 and digitally portion 55 and the low pass filter section 52 is multiplied with each other techniques using synchronous demodulation method to restore the original signal. The method of claim 1, wherein a reference signal is extracted from the discretized signal of the sound card, multiplied by the original signal, and a low pass filter is applied to restore the low frequency band signal. Line-in stereo terminal of the sound card by modulating the two or more different reference frequency waveforms corresponding to two or more independent signal inputs respectively with the modulation scheme mentioned in 1, and arithmetically adding the modulated signals to each other (44-1). A method of synchronously modulating a multi-channel signal by applying to one of the signal lines and simultaneously applying the reference frequency waveforms used in the modulation process (44-2) to the other signal line of the line-in stereo terminal. For a signal that is modulated and input in the manner mentioned in section 3, a reference waveform of the corresponding single frequency component is extracted using a band pass filter on the reference waveform signal 21-2 among the stereo signals discretized by the sound card, and then another stereo signal. A method for synchronous demodulation of two or more modulated signals by multiplying the digital signal (21-1) and passing a low pass filter to recover the original signal. 5. The method of claim 4, wherein the number of independent input signal channels is increased by very narrowing the bandwidth of the digital band pass filter.