KR20010083803A - Bio-Signal Modem using the Noncoherent Amplitude Modulation and Demodulation Method - Google Patents

Abstract

PURPOSE: A bio-signal modem is provided to achieve a digital signal by transmitting an analog signal to a computer with a sound card basically contained in the computer by adopting the asynchronous amplitude modulation method. CONSTITUTION: For embodying a signal modem for utilizing a sound card basically contained in the computer as an analog-digital converter, a signal modulation part(26) is embodied by adopting a reference frequency signal generator(43), a modulator(40) for multiplying a reference frequency signal by an original signal, a band-pass filter part(41) for setting the waveform of the modulated signal, and a gain controller(42) for adjusting the output level of the signal. The attained signal is applied to a sound card stereo terminal. A signal demodulation part(6) consists of a band pass filter(50), an absolute value calculator(51), a low-threshold pass filter(52), and a direct current breaker(53).

Description

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

The present invention deals with a method of asynchronous amplitude modulation and demodulation of 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. Analog amplitude modulation is used to convert low frequency signals to audible frequency signals, and asynchronous digital AM demodulation technology is used to recover the discrete signals from the sound card.

At this time, the channel multiplexing should be performed to obtain the signal of each channel by applying the multi-channel signal to the limited sound card input terminal. The present invention deals with a method of separating each channel by a frequency division method, and describes a method of properly utilizing the stereo input of a sound card to widen the dynamic range of a signal simultaneously input.

The present invention deals with a method of implementing an asynchronous amplitude modulation and demodulation method 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. It is of utmost importance to develop technology to make signal modems easier and simpler. Multiple channels must be supported at the same time. Line-in, the signal input terminal of a sound card, is a stereo terminal and can receive two kinds of signals at the same time. On the other hand, the biosignal input to the signal modem is usually two or more multichannels. Therefore, channel multiplexing is the most important technical factor because more than two channels of signal must be applied to one stereo input line.

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

2 is an amplitude modulation and demodulation block diagram of a single channel system according to the present invention.

3 is an amplitude modulation configuration for channel separation using a sound card stereo input line of a two channel system.

4 is a diagram illustrating a stereo two-channel signal demodulation scheme corresponding to the modulation scheme of FIG. 3.

5 is an amplitude modulation scheme for channel separation using one of sound card stereo input lines of a two channel system.

FIG. 6 is a diagram illustrating a two-channel signal demodulation configuration by stereo disconnection conforming to the modulation scheme of FIG. 5. FIG.

<Description of the code | symbol about the principal part of drawing>

5: sound card 6: digital signal demodulator

9: Biosignal modem 13: Line-in terminal

18: Stereo signal input to sound card

18-1: Right (left) signal line of stereo input line

18-2: Left (right) signal line among stereo input lines

21: Discrete stereo digital signal from sound card

21-1: Right (left) signal of discretized stereo digital signals

21-2: Left (right) signal among discretized stereo digital signals

22: Original signal restored through demodulation

22-1: Restored Channel-1 Signal 22-2: Restored Channel-2 Signal

40: amplitude modulator for amplitude modulation

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

42: Variable gain control for scaling the amplitude modulated signal for smooth input into the sound card

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

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

50: digital bandpass filter 51: digital absolute value calculator

52: digital low pass filter 53: digital DC circuit breaker

A functional diagram of a biosignal modem configured for acquiring a biosignal from a computer utilizing a sound card as an analog-to-digital converter is shown in FIG. 1. The present invention describes the configuration of the signal modulator 26 and the functional implementation method of the signal demodulator 6 accordingly. The amplitude modulation and demodulation method configured for the single channel biosignal is shown in FIG. 2. In FIG. 2, the signal applied to the modulator 26 is a DC offset signal. The degree of offset determines the degree of modulation of the amplitude modulation and the dynamic range of the signal. Since the demodulation method is asynchronous, the sign of the offset signal must be positive or negative. This signal is multiplied by the waveform (frequency fo) generated by the reference frequency generator 43 in the frequency mixer 40 to perform amplitude modulation. Usually, a square wave generator can be simply implemented, and when used as a reference waveform, a modulated waveform generates various higher order terms of fo. Since this causes noise during signal assist and can affect neighboring channel signals, especially in multi-channel, only the main component fo term is passed through the band pass filter. The signal output from this filter corresponds to the square wave modulation. This signal is controlled in the gain adjusting amplifier 42 and applied to the line-in of the sound card. The signal is then connected to the right (or left) of the stereo signal line.

The sound card 5 converts the input analog signal 18 into a digital signal 21. In the case of a single panel signal, the digital signal appears at the right (or left) of the stereo signal and acts on the digital band pass filter 50 to eliminate discretization errors and ensure a single signal channel. An absolute value operation 51 is performed on the digital data passing through the filter to full-wave rectify the signal. The rectified signal is passed through the digital low pass filter 52 having the cutoff frequency much lower than the carrier frequency fo and higher than the signal band to remove the carrier and recover the original signal of the low frequency band. This signal is a signal 54 with a direct current offset. DC offset is an artificial addition to a signal to perform asynchronous amplitude modulation and demodulation. However, this offset can be used to correct the channel signal size. In a multichannel system, it is important to uniformly calibrate the signal size of each channel. In the absence of an input signal, the variable gain controller of each channel can be controlled to have the same offset, or if it is already calibrated, it can be used as a signal to correct the difference caused by the difference in the frequency response of the sound card. . Since the frequency response of the sound card may not be the same at the reference frequencies used, the magnitude of the offset of the resulting demodulated signal may be different. If you connect the input signal to ground, the demodulated signal will only appear as an offset DC signal, and if the sound card's frequency response varies with the frequency used, this offset signal will also appear different. By multiplying the calibration factors so that the values are the same for multi-channel signals, the signals of all channels can be calibrated equally. However, since the original signal of the low frequency band does not have this offset, it is possible to recover to the correct signal through DC blocking 53 (22).

When two channels of signals should be obtained simultaneously, the method of FIG. 3 or 5 is modulated and the corresponding demodulation is performed by the method of FIG. 4 or 6. The modulation and demodulation method of FIGS. 3 and 4 uses two signal lines of the stereo terminal of the sound card at the same time. The modulation and demodulation method of each signal line is basically the same as that of FIG. In this case, the modulation carrier frequency may use one output from one waveform generator. Therefore, the characteristics of the following bandpass filter or gain control amplifier will be the same for each channel. However, the signal output is clearly distinguished because it is applied separately to the stereo input line of the sound card. The output 18-1 of channel-1 is connected to the right (or left) signal line of the stereo input line, and the output 18-2 of channel-2 is connected to the left (or right) signal line. The corresponding demodulation in FIG. 4 is similar. The channel-1 signal is recovered from the right (or left) digital signal 21-1 to a DC offset signal 54-1 and an original signal 22-1 through a digital demodulation process. Similarly, the channel-2 signal is recovered from the left (or right) digital signal 21-2 to the signal 54-2 and the original signal 22-2 offset by the DC through digital demodulation. Meanwhile, a method of loading two channels on one of the stereo signal lines is described with reference to FIG. 5 and a method of restoring the same is shown in FIG. The two-channel signal is amplitude modulated at different frequencies 43 and 43-1 to perform arithmetic synthesis 44 so that it can be applied to one signal line 18-1. At this time, the center frequencies of the band pass filters 41 and 41-1 of each channel are configured to match the corresponding modulation frequencies f0 and f1. The signal demodulation is basically the same as single channel demodulation. The only difference is that the channel separation is performed by a band pass filter tuned to the center frequency assigned to each channel. That is, in the demodulation, the input signal is the same, but the band pass filter 50-1 having the center frequency f0 obtains the channel-1 signal, and the band pass filter 50-2 having the center frequency f1 receives the channel-2 signal. Get a signal.

The two-channel signal acquisition method described in FIGS. 3 and 4 has twice the dynamic range of the signal than the method described in FIGS. 5 and 6. In order to obtain a multi-channel signal of more than three channels at the same time, these two methods must be used together to secure a wide dynamic range of the entire signal.

The present invention deals with a method of asynchronous amplitude modulation and demodulation of a signal modem for utilizing a sound card built in a computer as an analog-to-digital converter without a separate analog-to-digital converter. Using asynchronous amplitude modulation and demodulation, frequency division and channel multiplexing using sound card stereo signal lines can be used to implement a biosignal modem more simply and inexpensively.

Claims (7)

In implementing a signal modem 9 for utilizing a sound card that is basically built into a computer as an analog-to-digital converter without an analog-to-digital converter, the signal modulator 26 is connected to a reference frequency signal generator 43 and this signal. A modulator 40 to multiply the original signal, a band pass filter 41 for shaping the waveform of the modulated signal, and a gain controller 42 for adjusting the output magnitude of the signal are provided to the sound card stereo terminal 13. The signal demodulator 6 is implemented using a band pass filter 50, an absolute value calculator 51, a low pass filter 52, and a DC circuit breaker 53. Technology that uses asynchronous amplitude modulation and demodulation. The method according to claim 1, wherein signals modulated for a two-channel input signal are respectively connected to two signal lines of a sound card line-in stereo terminal to transmit a signal to the sound card and demodulate two stereo signals discretized in the sound card in the manner described above. Thereby separately acquiring two channel signals. The method according to claim 1, wherein amplitudes are modulated by using different reference frequency signals for two-channel input signals, and then arithmetically summed (44) and applied to one of the two signal lines of the sound card line-in stereo terminal. Signal is transmitted to the sound card, and the discrete signals are demodulated by band-pass filters 50-1 and 50-2 having different center frequencies. How to get separated. 4. The use of the same reference frequency for modulating two channel amplitudes. 4. The use of different reference frequencies in two channel amplitude modulation. A method of separating and acquiring signals of each channel at the same time for a signal input of three or more channels by a combination of two and three. A method for calibrating each channel signal difference based on the magnitude of the DC offset of each digitally demodulated channel signal (54) in a multi-channel input signal.