JPS6372208A - Signal amplification system - Google Patents

Abstract

PURPOSE:To obtain an inexpensive circuit amplifying a signal at a desired amplification factor by varying a control signal fed to a digital signal input terminal of a D/A converter connected between two amplifiers whose amplification factor is fixed. CONSTITUTION:A pulsating tone is inputted from a microphone 32 placed near a cuff 10, amplified by a fixed amplification factor, inputted to a reference voltage input terminal 52 of a D/A converter 36, where the signal is D/A- converted. The converted analog data is amplified (38), filtered (40), A/D- converted (42) and inputted to a CPU 30. The CPU 30 inputs control signals D0-D7 to a terminal 54 of the D/A converter 36 in response to the digital input to output an analog signal taking a reference voltage fed to the reference voltage input terminal 52 as a maximum value. Thus, the amplification factor is varied optionally by the simple circuit. This is suitable for a blood pressure measuring instrument.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a signal amplification method capable of amplifying a signal with a desired amplification factor.

BACKGROUND OF THE INVENTION When attempting to amplify a signal with a desired amplification factor, an operational amplifier or the like is generally used.

Problems to be Solved by the Invention However, in such an amplifier, it is usually impossible to arbitrarily change the amplification factor using a digital signal from a microcomputer or the like.

For this reason, ICs that can arbitrarily change the amplification factor depending on the digital signal are used, but since such ICs are usually expensive, it is not possible to construct a signal amplification method that amplifies the signal at a desired amplification factor at a low cost. The problem was that there was no.

Means for Solving the Problems The present invention has been made against the background of the above circumstances, and its gist is to provide a first amplifier that amplifies an input signal at a predetermined amplification factor; A reference voltage input terminal, a digital signal input terminal, and an output terminal are connected to the first amplifier. a D/A converter that outputs an analog signal from an output terminal, and a converter that is connected to the output terminal of the D/A converter and amplifies the analog signal output from the output terminal at a predetermined amplification factor. including two amplifiers;
The signal amplification method is configured to amplify the input signal input to the first amplifier with a desired amplification factor based on the signal supplied to the digital signal input terminal and output the amplified signal from the second amplifier. .

By doing this, the input signal is amplified by the first amplifier at a predetermined amplification factor and is input to the reference voltage input terminal of the D/A converter, and the input signal is also supplied to the digital signal input terminal. Based on the signal, the signal is adjusted to a predetermined magnitude having the magnitude of the input signal as its maximum value, and is output from the output terminal, and this signal is amplified by a predetermined amplification factor by the second amplifier.

Effects of the invention As a result, an amplifier with a fixed amplification factor and a D/A similar to the conventional one can be used.
By simply combining the D/A converter with the D/A converter and changing the signal supplied to the digital signal input terminal of the D/A converter, the input signal input to the reference voltage input terminal can be amplified with a desired amplification factor. Therefore, a signal amplification method for amplifying a signal at a desired amplification factor can be constructed at low cost.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 shows a case where the signal amplification method of the present invention is applied to a blood pressure measuring device. In the figure, 10 is a rubber bag-shaped cuff that is wrapped around the upper arm of the subject. cuff 1
0, a pressure sensor 12, an air pump 14, a throttle 16 and an electromagnetic on-off valve 18 for slow exhaust, and an electromagnetic on-off valve 20 for rapid exhaust are connected via piping 22, respectively. The pressure sensor 12 supplies a 4A pressure signal SP representing the pressure within the cuff 10 to a low pass filter 26 via an amplifier 24. The low-pass filter 26 discriminates a signal representing steady pressure included in the pressure signal SP, and supplies a cuff pressure signal SK representing the pressure of the cuff 10 to the CPU 30 via the A/D converter 28.

A microphone 32 is provided near the cuff 10. The microphone 32 detects the pulse sound (K sound) generated from the upper arm of the subject, and sends the K sound signal SO to the amplifier 3.
4, the signal is supplied to a bandpass filter 40 via a D/A converter 36 and an amplifier 38.

The bandpass filter 40 passes a signal having a frequency component of, for example, about 30 to 80 Hz, and sends the passed sound signal SO to the CPU 3 via the A/D converter 42.
Supply to 0.

The CPU 30 is connected to the ROM 44 via the data bus line.
RAM 46, display 48, and output interface 5
It is connected to the air pump 14 and the electromagnetic on-off valve 18 .
20 while performing a series of blood pressure measurement operations,
The blood pressure value is determined based on the sound signal SO, the cuff pressure signal SK, etc., and the blood pressure value is displayed on the display 48. Note that a detailed explanation of the above blood pressure measurement operation will be omitted since it is not necessarily necessary for understanding the present invention.

The D/A converter 36 has a reference voltage input terminal 52 and a DO-D to which an 8-bit signal is supplied in this embodiment.
7 eight digital signal input terminals 54 and output terminal 56
The reference voltage input terminal 52 is connected to the amplifier 34, and the output terminal 56 is connected to the amplifier 38. Therefore, in this embodiment, the amplifier 34 constitutes a first amplifier, and the amplifier 38 constitutes a second amplifier. Here, the CPU 30 is configured such that, for example, a circuit (not shown) inputs the sound signal SO from the microphone 32 at the beginning of the blood pressure measurement, and inputs a predetermined digital signal corresponding to the magnitude of the sound signal SO to the CPU 30. is supplied from the CPU 30' to the digital signal input terminal 54 of the D/A converter 36 during the period of blood pressure measurement. As a result, the D/A converter 36
Based on the digital signal supplied to the digital signal input terminal 54, the input signal input to the reference voltage input terminal 52 is converted to the voltage Vi of the input signal according to the following equation (1).
is outputted from the output terminal 56 as a signal of voltage Vo having the maximum value.

■o=(X/255)×■i...(1) In addition, X
is the decimal conversion number of the digital signal supplied to the digital signal input terminal 54, and in this embodiment, it is 0 to 2.
55, 256 types of values can be taken. Therefore, the above
/255 indicates the amplification factor by the D/A converter 36, and the minimum value is O1 and the maximum value is 1.

Here, the input voltage of the sound signal SO input to the amplifier 34 is Vin, the amplification factor of the amplifier 34 is 61, the amplification factor of the amplifier 38 is 02, and the output voltage output from the amplifier 38 is V.
If the amplification factor of the entire amplifier 34.38 and D/A converter 36 is G, then the sound signal SO output from the microphone 32 is a signal supplied to the amplifier 34.38 and the digital signal input terminal 54. Based on this, the signal is amplified according to the following equation (2).

G = Vout / V 1n = G1xG2x (X/255) (2) Therefore, in equation (2), by changing X, that is, the digital signal supplied to the digital signal input terminal 54 is changed as appropriate. By doing this, the amplification factor of the D/A converter 36 can be varied in a plurality of steps (256 steps in this embodiment) within the range of 0 to 1, so that the amplification factor G1. By appropriately determining G2, the sound signal SO output from the microphone 32 is amplified by a desired amplification factor G. In this embodiment, the portion surrounded by the dashed line in FIG. 1, that is, the amplifier 34.3
8 and the D/A converter 36 constitute an amplification device based on the signal amplification method of the present invention. FIG. 2 shows an example of a variable range of the amplification factor G by such an amplifier.

In the figure, for example, when G1 is 1.5 and G2 is 2, that is, the amplification factor GIXG by the amplifier 34.
Variable range r of amplification factor G when 2 is 3 (0 to 3)
The thin line is the amplification factor G when X is 255.
(3) is shown.

In this way, according to this embodiment, the amplifier 3 with a fixed amplification factor
4.38 and a D/A converter 36 similar to the conventional one, and by simply changing the signal supplied to the digital signal input terminal 54 of the D/A converter 36, from the reference voltage input terminal 52. Since the input signal that is input is amplified with a desired amplification factor, a signal amplification method that amplifies the signal with a desired amplification factor can be constructed at low cost.

In addition, in the above-mentioned embodiment, the amplification factor of either one of the amplifiers 34 and 38 may be 1.

That is, one of the amplifiers does not need to be substantially provided, and even in this case, it is sufficient that the input signal can be amplified by the desired amplification factor by the other amplifier and the D/A converter 36. be.

Further, in the above embodiment, eight digital signal input terminals 54 of the D/A converter 36 are provided, but this is not necessarily necessary, and the number may be increased or decreased as necessary.

Furthermore, in the above-mentioned embodiments, the case where the signal amplification method of the present invention was applied to a blood pressure measuring device was explained.
Of course, the signal amplification method of the present invention can be applied to devices other than blood pressure measuring devices.

In addition, various changes may be made to the present invention without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a main part of a control circuit of a blood pressure measuring device to which the signal amplification method of the present invention is applied. FIG. 2 is a diagram showing an example of the variable range of the amplification factor by the signal amplification method shown in FIG. 34.38: Amplifier 36: D/A converter 52: Reference voltage input terminal 54: Digital signal input terminal 56: Output terminal

Claims (1)

[Claims] A first amplifier that amplifies an input signal at a predetermined amplification factor; a reference voltage input terminal, a digital signal input terminal, and an output terminal connected to the first amplifier; a D/A converter that outputs a digital signal input from a terminal as an analog signal having a maximum value of a reference voltage applied to the reference voltage input terminal from the output terminal; and the output of the D/A converter. a second amplifier connected to the output terminal and amplifying the analog signal output from the output terminal at a predetermined amplification factor, the input signal input to the first amplifier being supplied to the digital signal input terminal; A signal amplification method, characterized in that the signal is amplified with a desired amplification factor based on the signal and outputted from the second amplifier.