JPS6057767B2 - amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit, and more particularly to an amplifier circuit for amplifying the output of a Hall element, which is a magnetizing element, and an object of the present invention is to provide an amplifier circuit with excellent voltage reduction characteristics. It is in.

2. Description of the Related Art Conventionally, a magnetic sensing element, a so-called Hall element, which utilizes the Hall effect, has been used to detect various rotations, such as detecting the rotation of a reel stand in a tape recorder and detecting the rotation of a turntable drive motor in a record player.

Various types of amplifier circuits are available for amplifying the output AC signal of the Hall element, but all of these require a high voltage as the operating power supply voltage.
This has disadvantages such as the fact that the output signal of the Hall element is easily affected by the offset voltage when the voltage is reduced. The offset voltage of the Hall element is an unbalanced voltage of the output DC voltage of the amplifier circuit, and the output DC voltage and voltage of the amplifier circuit are the values obtained by multiplying the offset voltage by the amplification degree of the amplifier circuit. Therefore, if the output AC signal voltage of the Hall element is not sufficiently large with respect to the offset voltage, the output end of the amplifier circuit will be affected by the offset and will not be able to transmit the AC signal.
Therefore, it is common practice in low voltage Hall element amplifier circuits to cut off the direct current using a capacitor and then amplify it. To explain such a conventional amplifier circuit using FIG. 1, 1 to 3 are PNP transistors, and 4 to 3 are PNP transistors.
9 is an NPN transistor, 10 and 11 are diodes, 1
2 to 16 are resistors, 17 is a Hall element (transistor 4,
The base of 5 is connected to the output terminal), 18 is the capacitor, 19 is the power supply, 20 is the output terminal of the amplifier circuit, 2
1 is a power supply terminal, and 22 is a ground terminal. transistor 4
, 5 constitute a differential amplifier, transistor 3 is for amplification, and transistor 6 constitutes an emitter follower circuit. Resistors 12 and 13 have the same resistance value, and resistor 14 applies feedback from the emitter of transistor 6 to the emitter of transistor 5, and the output DC voltage of terminal 20 is set to be equal to the emitter voltage of transistor 5. ing. Diodes 10, 11 and transistors 7-9 constitute a current source. Transistors 4, 5
The emitter voltage of is 112Vcc-■BE (■.Power supply voltage, VBE; transistor base-emitter voltage)
Therefore, the output DC voltage also has the same value. Therefore, when the power supply voltage A becomes 2VBE, the output DC voltage is ν×2
VI3. -■ The offset voltage of the Hall element 17 becomes zero due to BO and poor voltage reduction characteristics. 9 is the output end 20
Taking into consideration that this occurs, the lower limit power supply voltage that enables normal operation of this amplifier circuit needs to be at least 2VBE+Voff or more.

The present invention has improved the above-mentioned drawbacks, and one embodiment thereof will be described with reference to FIG. 2 showing a specific circuit thereof and FIG. 3 showing an equivalent circuit of this circuit.

Note that in FIGS. 2 and 3, the same components as those in FIG. In Figure 2. 23 to 27 are PNP transistors, 28 and 33 are diodes, 29 to 32 are NPN transistors, and 34 to 43 are resistors. Next, in FIG. 3 which equivalently shows the circuit of FIG. 2, 44 and 45 are Hall elements 17 including the resistor 34.
equivalent resistance, 46 is the transistors 23 to 25, 30, 3
1, diode 33, and resistors 39 and 40 ■Bε, which is (2+n)TCn
; Arbitrary number, ■BE: voltage between the base and emitter of the transistor 31, R: resistance value] is supplied.

47 is a current source composed of a transistor 29 and a resistor 37, and 48 is a current absorber composed of a diode 28 and a resistor 36.
In any case, a constant current flows through the VBE intrusion source.

Regarding the resistors 35 and 43, if the value of the resistor 43 is r, the resistor 35 is set to a value of (1+n)r, and the resistor 38 is set to a value of (1+n)r. is set to Further, transistors 26 and 27 constitute a differential amplifier, transistor 32 is for amplification, and diode 28, transistor 29, and resistors 36 and 37 are current mirror loads for improving common mode resilience. In the above embodiment, the collector current 1 of the transistor 30 is equal to [R39; the value of the resistor 39],
The current from the current source 46 supplied to the differential amplifier composed of transistors 26 and 27 is 31.

If the value of resistor 35 is set to twice that of resistor 43,
The current flowing through the resistor 35 is twice the current flowing through the resistor 35. However, since the transistors 26 and 27 constitute a differential amplifier, both transistors 26 and 27 act to cause the same current to flow, so that a current I flows through the feedback resistor 38. At this time, if the resistor 38 is set to the same value as the resistor 39, the voltage drop across the resistor 38 will be B5. Therefore, the base voltage of transistors 26 and 27 is . [■. . ; power supply voltage], the emitter voltage of the transistor 27 is νVc
O+■BO [■Kei; base-emitter voltage of transistor 27], which appears at the output terminal 20 after receiving the voltage drop VBE of the resistor 38, the output DC voltage becomes M■
. becomes. Similarly, set the base voltage of transistors 26 and 27. CN; any number], the output DC voltage is blue Vc
It becomes O. When the power supply voltage Vcc is 2VBE, the DC output voltage from the terminal 20 is VBE, and the offset voltage of the Hall element 17 is . Ff is ■. If Ff×BE, the AC output of the Hall element 17 can be reliably amplified and taken out. By connecting the resistor 34 in series with the Hall element 17, for example, if Rvcc, the power supply voltage ■. is 2V
When BB, the emitter voltage of transistor 27 is (VBB
Therefore, the voltage reduction characteristics are improved by 6 VBO. In the above embodiment, the differential amplifier was composed of PNP transistors, but
Needless to say, this is the same even if it is configured with NPN transistors. As explained above, according to the amplifier circuit of the present invention, the reduced voltage characteristics can be improved with a simple circuit configuration, and if this is used to amplify the output AC signal of the Hall element, the output signal can be reliably amplified.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional amplifier circuit, FIG. 2 is a circuit diagram showing an amplifier circuit according to an embodiment of the present invention, and FIG. 3 is an equivalent circuit diagram thereof. 20... Output end, 26... (second)
Transistor, 27... (first) transistor, 32... (third) transistor, 35...
...(second) resistance, 38...(third)
Resistor, 43... (first) resistor.

Claims (1)

[Claims] 1 (1/N)V_c_c [N: arbitrary number, V_c_c:
A voltage of [power supply voltage] is applied to each base of the first and second transistors constituting the differential amplifier, and an input signal is applied between each of the bases, and a voltage of the value that becomes the emitter of the first transistor is applied. One end of a second resistor of (1+n)r [n; arbitrary number] is connected to the emitter of the second transistor, and the other ends of the first and second resistors are connected to the emitter of the second transistor. Common connection and I=(2+n)・V_
A current source of B_E/R [V_B_E: voltage between the base and emitter of the transistor constituting the current source] is connected, the collector of the second transistor is connected to the first reference voltage point through the first load, and the collector of the second transistor is connected to the first reference voltage point through the first load. The collector of one transistor is connected to the first reference voltage point through a second load, the collector is further connected to the base of a third transistor, and the emitter of the third transistor is connected to the first reference voltage point. The collector of this third transistor is connected to a second reference voltage point to which V_c_c is applied through a third load, and the emitter of the first transistor and the collector of the third transistor are connected to R/n. An amplifier circuit characterized in that the amplifier circuit is connected through a third resistor having a value of , and the collector of the third transistor is used as an output terminal. 2 Connecting the bases of the first and second transistors constituting the differential amplifier to the first and second output terminals of the Hall element,
2. The amplifier circuit according to claim 1, wherein the third terminal of the Hall element is connected to the second reference voltage point, and the fourth terminal is connected to the first reference voltage point. 3. According to claim 2, a resistor is inserted between the third terminal of the Hall element and the second reference voltage point, or between the fourth terminal and the first reference voltage point. Amplification circuit.