SU1569876A1 - Device for magnetic recording of analog signals - Google Patents

Abstract

The invention relates to instrumentation, in particular to a magnetic recording technique, and can be used in portable magnetic recording equipment designed for continuous, continuous recording of analog signals (for example, electrocardiograms) in real time. The purpose of the invention is to improve the recording quality by reducing nonlinear and intermodulation distortion, as well as reducing the size and weight of the device. Rectangular pulse generator 5 generates pulses, of which control unit 6 generates signals for controlling analog multiplexer 2, which alternately connects to the magnetic recording head 3 an analog signal from the output of recording amplifier 1 and supply voltages + E and -E from buses 8 and 9 . Due to the integrating effect of the inductance of the magnetic head and symmetric voltages + E and -E is formed by high-frequency bias current (J _n) having a symmetrical triangular shape, and this current is summed with a magnetic head samples sig records (J _s ), formed in the intervals between opposite-polarity pulses + E and -E, i.e. separately in time with respect to the recorded signal, which allows reducing nonlinear and intermodulation distortions, as well as modulation noise. The absence of a separate high-frequency bias generator and band-pass filters (to eliminate the relationship between the bias generator and the recording amplifier) makes it possible to simplify the design of the device, reducing its dimensions and weight. 2 Il.

Description

The invention relates to instrument making, namely, to a magnet-pop recording technique, and can be used in portable magnetic recording equipment designed for continuous, continuous recording of analog signals (for example, electrocardiogram) in real mode.

The purpose of the invention is to improve the recording quality by reducing the nonlinear and intermodular distortions, as well as reducing the size and the device.

Figure 1 shows the structural scheme of the device proposed; Figure 2 shows signal plots explaining the operation of the device.

The device (FIG. 1) contains a recording amplifier 1, an analog multiplexer 2, a recording magnetic head 3 coupled to a 4-digit recording medium, a square pulse generator 5, a control unit 6, a capacitor 7, a single supply voltage bus 8 (for example , positive) polarity + E, bus 9 supply voltage of the other (negative) polarity -E, common bus 10 and measuring resistor 11.

The output of the recording amplifier 1 is connected to the second and fourth information inputs of the analog multiplexer 2, as well as to a capacitor, another output connected to the bus bar 10. The first and third information inputs of the anapog multiplexer 5 are connected to the + E 8 bus and the E 9 bus. these voltages and the control inputs are connected to the outputs of the control unit 6, the input of 5 square-wave pulses connected to the generator output.

The output of the analog multiplexer 2 is connected to a recording magnetic head 3, the other output of which is connected to the common bus Y via a measuring resistor 11.

The device works as follows.

The generator 5 of rectangular pulses generates pulses (Fig. 2a) of a sufficiently high frequency fr (on the order of several tens of kHz), which are fed to the input of control unit 6, made, for example, in the form of a two-bit counter. Depending on the values of two-digit

the binary code arriving at the control inputs A and B of the analog multiplexer 2, the latter connects one of the four information inputs DO - PZ to its output, immersed in the recording magnetic head 3.

When a two-digit code 00 (A O, B 0) is fed to the control inputs of the analog multiplex- oo, the first input (DO) of the multiplexer and the bus 8 of the supply voltage of positive polarity are connected to the output

5 E is connected to the magnetic recording head 3, in which the inductance increases the current with a constant time determined by this inductance 7, mg, the resistance of the open channel of the multiplexer RU, which usually does not exceed 100 Ω, and the resistance of the measuring resistor 11 (the value of which is usually not more than

5 10 ohms and practically does not affect the operation of the device).

The current in the magnetic head increases with speed

thirty

   §. (i1 dt L L, - U;

1 mg

where 1 mg is the current in the magnetic head; - voltage on magnetic

head;

E is the power supply voltage.

The value of the current i MP determines the magnitude of the bias current 1P, which usually does not exceed 1 mA. The amplitude of the current i is two times higher than the effective value of the current, since the current i increases and decreases linearly.

Since the voltage E of the power source is several volts, in the expression (1) we can neglect the term (i Ru r Ru), which is the fraction of a volt. Then

y - to t--. (2) dt iwr

For the time interval t Ј

current,

flowing through the recording magnetic head, reaches

- E

MG - tS

mg

(3)

When the control inputs of multiplexer 2 receive a code Y (A 1,

8 0), the first input of the multiplexer is disconnected from its output and the second input of the multiplexer 3 connected to the output of the recording amplifier 1 and the capacitor 7 is connected to the latter. Current img in the magnetic head

3 begins to decrease linearly and due to the presence of a capacitor 7 supporting the following current flow, the decrease rate iwr does not affect the large output impedance of recording amplifier 1, and this rate of current decline can be set equal to the current rise rate of 1mG.

In the recording magnetic head 3, in addition to the falling current iMr, the low-frequency current of the recorded signal 1E also flows, which is formed by the recording amplifier 1.

At the same time, the current i mg performs the functions of the bias current, and the low-frequency current of the recording signal (Fig. 2d creates residual magnetization on the magnetic recording medium 4.

Similar processes considered in the first half of the period of the generated recording signal S (t) also occur in the second half of this period (Fig. 3), with the control signal codes 01 (A 0, B 1) and 11 (A 1; B 1 ), while the recording magnetic head 3 is connected by an analog multiplexer 2 to the bus

9 of the negative-polarity supply voltage -E and the current increases and decreases now with the opposite polarity in relation to the first half of the period.

Thus, from the rectangular voltage pulses at the input of the analog multiplexer 2, due to the integrating action of the recording magnetic head 3, a high-frequency triangular-shaped biasing current is generated.

The summation of the recording and bias currents occurs in the magnetic head at the moments of connecting the output of the recording amplifier 1 to it.

The magnitude of the bias current with its triangular shape

15698766

and one period of the pulses produced by the generator 5 rectangular pulses (Fig. 2a). Then the formula (4) takes the form

1 p

2L

Mg

(five)

ten

or

In

2L

(6)

Mr

five

0

five

0

where Tr and f are the period and frequency of the generator of rectangular pulses, respectively.

It can be seen from expression (6) that the high-frequency bias current at a given inductance value of the recording magnetic head 3 can be controlled by varying the amplitude of the rectangular pulses of the generated recording signal S (t), and the amplitude of the pulses of both polarities must be simultaneously changed, otherwise the level of non-linear distortions increases of the recorded signal due to the bias current asymmetry.

In practice, it is most advantageous to regulate the magnetisation current in this device by changing the frequency fr of the generator 5 rectangular pulses, since according to (6) the magnitude of this current is inversely proportional to the frequency fr.

Thus, in the proposed device (FIG. 2d), the output recorded signal V (t) is subjected to a discrete-to-analogue Q-conversion, namely the process of periodic sampling of fragments of this signal with frequency fr, and the sampling time of each fragment V (t) is equal to the pause time (point Ј) between adjacent fragments. During the pause, rectangular pulses of positive or negative polarity are formed (shown in Fig. 2 by a dotted line) with the help of control signals (Fig. 26, c) generated by control unit 6.

five

five

0

- -one; MG

E,,

W

l

with,

In device C, the sampling time duration is equal to one quarter of the period of the write signal S (t)

The sampling frequency F- in accordance with the Kotelnikov-Shannon theorem should be no less than twice, greater than the highest (FB) frequency of the input recorded signal V (t), to simplify the reproduction process, it is better to choose a) FB times. In the device

(7)

(5 ... 10) F

ft

(eight)

Taking into account expressions (6) - (8), such parameters as the highest frequency F g of the recorded signal V (t), frequency fr of the square pulse generator, amplitude E of the rectangular pulses (i.e., receiving + E and -E) reading sources operating in the pauses between the fragments of the sampled input signal V (t).

Since the high-frequency magnetization current has a symmetrical triangular shape (which is easily accomplished with supply voltage symmetry, -tE and -E) and is formed due to the integrating effect of the inductance of the recording magnetic head, and this formation occurs from , acting in the intervals between the samples of the recording signal (i.e., degraded and alternately in time relative to the recorded signal), nonlinear distortion, modulation noise and intermodulation distortion are reduced and.

The absence of a separate high frequency pickup generator and bandpass filters (to eliminate the relationship between the bias generator and the recording amplifier) allows

to simplify the design of the device and reduce its size and weight.

Claims (1)

Formula invented and A magnetic recording device for analog signals, containing a recording amplifier that records magnetic a head coupled to a magnetic recording medium, and a high-frequency biasing generator, characterized in that, in order to improve the recording quality by 5 reduce the nonlinear and intermodulation distortions, as well as reduce the size and weight of the device, an analog multiplexer, a control unit and a capacitor are inserted into it, and a high-frequency biasing oscillator is made in the form of a square pulse generator, the first information input of the analog multiplexer is connected to the bus 5 power supply voltage of one polarity, the second and fourth information inputs - with the output of the recording amplifier, and with a capacitor, the other output connected to the common bus, 0, the third information input is with the bus voltage of the other polarity, the control inputs are with the outputs of the control unit, the input of which is connected to the generator output pr,. The angle of the analog multiplexer is connected to one of the inputs of the recording magnetic head, the other input of which is connected to the common bus through a measuring resistor. a i PPPPPPPPPPG t p p p p p p g p t t g t ЩЩ %% 2 & t ln + Е / g; t FIG. g