SU1458965A1 - Inductive sensor signal amplifier - Google Patents

Abstract

The invention relates to radio engineering. The purpose of the invention is to increase the gain and reduce the noise level. The device contains five transistors (T) 1,2,3,4,5, three resistors (P) 6,7,8. And inductive sensor (ID) 9. To achieve the goal, ID 9 is connected between the base and the collector T 1, P 7 is connected between the collector .T 1 and 3. , Base, collector T 5 connected to the collector T 2 and a common bus, respectively. The emitter T 5 is the output of the device and through P 8 it is connected to the base T 4. The indicated inclusion ID 9 excludes the use of an input coupling capacitor in the proposed scheme, which is a source of low-frequency noise due to the presence of leakage currents, which leads to a decrease in noise figure of 1 , 5-2 times. T 5 performs two functions in the circuit: serves as an output emitter follower and increases the internal resistance of the resistive load, as a result of which the gain of the device increases. 1 il. O + S (L o VyzhvZ sd ckh Oi sd

Description

The invention relates to radio engineering and can be used in amplifiers of signals of various types of inductive sensors that are not connected to a common bus, in particular in amplifiers for reproducing tape recorders.

The purpose of the invention is to increase the gain and reduce the noise level.

The drawing shows a circuit diagram of an inductive sensor signal amplifier.

The amplifier of the signals of the inductive sensor contains the first, second, third, fourth and fifth transistors 1-5, respectively, the first, second and third resistors 6-8, respectively, and the inductive sensor 9.

The amplifier works as follows.

An input signal from an inductive sensor 9, which is extruded, for example, in the form of a magnetic head, a secondary winding of a transformer, an electromagnetically sound pickup or other inductive element with a small internal resistance across DC, is supplied between the base and the collector of the first transistor 1. Constant current, the transistor 1 acts as a diode bias of the second transistor 2, which ensures the temperature independence of the collector current of the second transistor 2. This is explained by a small internal resistance nduktivnogo sensor 9, whereby the collector and the base of the first transistor 1, a DC combined and it is included as di- odes. However, the alternating current input signal transistor 1 is turned on. As the amplifier cascade according to the circuit c, common collector (OK). Since ... the input signal acts between the base and the collector, it is removed from the collector, i.e. the common electrode between the input and the output is the collector of the first transistor 1. In this case, the second resistor 7, included in the collector circuit of the first transistor 1, simultaneously plays the role of the current-providing circuit element and the load of the first stage on the first transistor 1. This cascade is the zero voltage of the collector - the base of the first transistor 1, but despite this it works in active mode.

since the collector-emitter voltage is 0.6-0.7 V, which is far from the field of silicon transistors. With such a low voltage, the linearity of the transistor is preserved only for small input signals characteristic of reproducing magnetic heads, electromagnetic pickups and other inductive sensors of weak signals.

Another feature of the cascade with OK on the first transistor 1 is high input impedance, which is explained not only by the property of the cascade with OK to have a higher input impedance, but also the absence in the proposed circuit of resistors of the basic bias, which in known circuits significantly reduce the input resistance and increase the coefficient of schum.

The inclusion of an inductive sensor excludes the use of an input coupling capacitor in the proposed scheme, which is a source of low-frequency noise due to the presence of leakage currents and an increase in the module impedance of the signal source at low frequencies. The separation capacitor can also be eliminated in the known circuits, however, for this it is necessary to use two power sources, which complicates the amplifier, and in some cases is impossible (for example, in portable tape recorders). In the proposed scheme, despite the use of a single power source, the separation capacitor is excluded, which leads to a decrease in the noise figure by 1.5-2 times

The power-amplified input signal from the collector of the first transistor 1 is fed to the base of a preamplifier amplifier, implemented on the second transistor 2 according to a circuit with a common emitter. The active load of the second transistor 2 is made on the fourth transistor 4 with a diode offset on the third transistor 3, and the diode current on the third transistor 3 is set using the second resistor 7. A feature of the active load that distinguishes it from the known ones is the use of the fifth transistor 5 The transistor is complete in circuit two. functions: serves as an output emitter follower and increases the internal resistance of the active load, in

the result is increased device gain. The latter is explained by the fact that the third, fourth, and five transistors 3, 4, and 5 are connected according to the scheme of an improved version of the current source with a diode bias, which due to negative feedback through the third resistor 8 has increased internal resistance . The difference of the proposed circuit from the known one is in the presence of the first and third resistors 6 and 8, which somewhat reduce the internal resistance, which remains significantly larger than in the prototype. The first resistor 6 is needed to scale the currents flowing through the third and fourth; transistors 3 and 4, which is connected with the flow through the third transistor 3 of the additional emitter current of the fifth transistor 5. To ensure that the collector currents of all transistors of the circuit are approximately equal, the collector current of the third transistor 3 must be twice as high than the collector current of the fourth transistor 4.

These distinctive features lead to an increase in the gain factor of the proposed scheme by a factor of 2–2.5, a decrease in the noise figure by 1.5–2 and a significant simplification compared to the prototype.

0

0 b

Claims (1)

Invention Formula An inductive sensor signal amplifier containing the first and second transistors of one structure, the emitters of which are connected to a common bus, and the collector of the first is connected to the base of the second transistor, the third and fourth transistors of another structure, the emitter of the fourth transistor, through the first resistor, and the emitter of the third transistor directly connected to the power supply bus, the collector and the 5 base of the third transistor are combined and connected to the base of the fourth transistor, the collector of which is connected to the collector of the second transistor Ora, fifth transistor, as well as second and third resistors, different from the fact that, in order to increase the gain and decrease the noise level, an inductive sensor is connected between the base and collector of the first transistor, the second resistor between the collector of the first and third The transistors, the base and the collector of the fifth transistor are connected to the collector of the second transistor and the common bus, respectively, and the emitter of the fifth transistor is the output of the amplifier and through the third resistor is connected to the base of the fourth transistor. 0