JPH07109968B2 - Amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention is directed to a VTR (video tape recorder) and a DAT.
The present invention relates to an amplifier circuit suitable for integration for amplifying a head reproduction signal in a magnetic recording / reproducing apparatus such as (digital audio tape recorder).

(Prior Art) FIG. 7 shows an amplifier circuit conventionally used for amplifying a head reproduction signal in a magnetic recording / reproducing apparatus. Normally, the circuit shown in FIG. 7 is integrated into an IC, and the portion surrounded by the dotted line in the drawing is the internal circuit of the IC.

The base of the input transistor Q1 is the power supply Vc
Biased with a voltage divided by c. Usually, this bias value is often 1/2 Vcc in order to obtain a large dynamic range during recording. The emitter of the transistor Q1 is pulled by a constant current source I1 with a constant current, and this is the operating current of the transistor Q1.
At the same time, since it is grounded by the capacitor C3 via the pin P2 of the IC, the AC operation is a grounded-emitter amplifier circuit. The transistor Q2 is cascode-connected to the transistor Q1, and its base potential is constant, so that the emitter potential is also constant. Therefore, of the collector current of the transistor Q1, the amount shunted to the resistor R3 is constant, and the remaining current flows to the transistor Q2. This is because R4 >> re
This is because it is necessary to set VT / I1 as (Q1), and without the resistor R3, the voltage drop in the resistor R4 becomes too large. VT is a thermal voltage, which is about 26 mV at room temperature. The base of the transistor Q2 is AC-grounded to the power source Vcc by the capacitor C4 via the pin P3, and thus is a grounded base circuit. Basic operation is possible without the capacitor C4, but in reality the signal to be handled is extremely small,
It is necessary to add in order to improve noise characteristics. Transistor Q3 has an emitter-follower for impedance exchange.

Although one amplification stage is formed as described above, since the gain is not sufficient by itself, another amplification stage is necessary, which is the differential amplification circuit A1. The emitter, which is the output of the transistor Q3, is connected to the base, which is the input of the transistor Q10. The transistor Q10 is a simple emitter follower, and its output is connected to the non-inverting input terminal of the differential amplifier circuit A1. The output of the differential amplifier circuit A1 is a transistor
Transistors Q4, Q5 with current mirror load of Q6, Q7
Is added to the base of transistor Q4 of the differential amplifier circuit consisting of. The reference voltage V1 is connected to the base of the other input transistor Q5, and the output is connected to the base of the emitter follower transistor Q8. Transistor
A signal corresponding to the output signal (AC) of the differential amplifier circuit A1 is on the collector current of Q5 and Q7, but it is grounded by the capacitor C5 via the pin P5 of the IC, so the base potential of the transistor Q8. Becomes DC potential, and transistor Q8,
This DC potential is applied to the inverting input terminal of the differential amplifier circuit A1 via the emitter follower of Q9.

The output path of the differential amplifier circuit A1 → the base of Q4 → the collectors of Q5 and Q7 → the base of Q8 → the base of Q9 → the inverting input terminal of A1 stabilizes the output potential of the differential amplifier circuit A1. is there. For example, when the output potential V _OUT of the differential amplifier circuit A1 is higher than the reference voltage V1, the base potential of the transistor Q4 becomes higher than the base potential of the transistor Q5, so that the collector current of the transistor Q5 is higher than that of the transistor Q5.
More than Q4. The collector current of transistor Q4 is Q
IC, (Q5)> I, because it will be folded by the current mirror of 6, Q7
It becomes C (Q7), and the base potential of the transistor Q8 works in the direction of increasing. This is the emitter of transistors Q8 and Q9.
The potential of the inverting input terminal of the differential amplifier circuit A1 is raised via the follower, and the output voltage V _OUT is lowered accordingly. That is,
When the output potential V _OUT of the differential amplifier circuit A1 is higher than the reference voltage V1, the output voltage V _OUT is lowered by the action of the feedback path described above. On the contrary, when the output voltage V _OUT is lower than the reference voltage V1, the output voltage V _OUT is raised by the action of the feedback circuit, and eventually V _OUT becomes equal to V1.

The signal applied to the IN terminal is applied to the input pin P1 of the IC via the input coupling capacitor C1. This signal is also applied to the base of the transistor Q1, but the transistors Q1 and Q2 are cascode-connected, and the signal applied to the base of the transistor Q1 appears in the collector of the transistor Q2 multiplied by I1 ・ R4 / VT. . This amplified signal is impedance-converted by the emitter / follower of the transistor Q3 and transmitted to the next stage, and is also input from the pin P4 via the capacitor C2 and the resistor R6 to the transistor on the input side.
Returned to the base of Q1. This feedback path lowers the input impedance of the amplifier circuit by negative feedback and Q-dumps the resonance peak due to the inductance of the head connected to the IN terminal and the input capacitance of the transistor Q1 (feedback damping). The damping amount can be changed by the resistor R6, and the impedance varies depending on the type of head. Therefore, it is necessary to adjust the resistor R6 to an optimum value for each type of head. On the other hand, the transistor
The signal that has passed through the emitter follower of Q10 is the differential amplifier circuit A
It is amplified by a predetermined amplification factor in 1 and is output from the output pin P6 of the IC.
Appears at the terminal.

In the circuit described above, five capacitors C1 to C5 are required in the IC, and the pins of the IC except the power source Vcc and the ground GND are required to have six pins P1 to P6. Since the element of the capacitor C1 and the resistor R6 is connected to the input pin P1 of the IC, it is likely to be influenced by the outside due to the pattern, the arrangement of parts and the like. Since the constant current I1 is a relatively large current,
If the resistors R1 and R2 are not made small, the base bias voltage of the transistor Q1 will be affected by the base current of the transistor Q1. Therefore, if the resistors R1 and R2 are set small, the circuit waste current will increase. Further, there is a problem that thermal noise generated from the resistors R1 and R2 is directly applied to the input.

(Problems to be solved by the invention) In the conventional amplifier circuit, not only the number of capacitors and the number of pins of the IC are large in order to be integrated into an IC, but also the pattern by the elements connected to the input pins of the IC, the parts layout, etc. It was susceptible to external influences. Furthermore, if the bias resistance connected to the input of the input transistor is not made small, the bias voltage will be deviated by its own base current, and if it is made small, the circuit's dead current will increase, and the thermal noise generated in this will increase. There was a problem that the voltage was applied to the input transistor.

This invention eliminates the above-mentioned problems, and
It is an object of the present invention to provide an amplifier circuit capable of reducing the number of pins of an IC, making it less susceptible to external influences, and reducing the wasted current of the circuit.

[Structure of the Invention] (Means for Solving the Problems) In an amplifier circuit of the present invention, a first transistor whose emitter is grounded via a first capacitor and a cascode connection to the first transistor, and a base A second transistor having the same polarity as the transistor grounded via a second capacitor, a first resistor connected between the emitter of the transistor and a first reference potential, and a base of the second transistor. A second resistor connected between the first reference potential and the second resistor, and a third resistor connected between the collector of the second transistor and the first reference potential,
A voltage detection circuit in which the emitter of the first transistor is connected to one input, the other input is connected to a second reference potential, and the output is connected to the base of the second transistor; A first differential amplifier circuit connected to the base of the second transistor and the other input connected to the collector of the second transistor, and the output of the differential amplifier circuit is returned to the base of the first transistor. A feedback circuit having a fourth resistor and a fifth resistor connected in series, and a connection point between the fourth resistor and the fifth resistor is grounded via a sixth resistor and a capacitor. And a feedback circuit.

(Function) By using the above-described means, the feedback path for feedback / damping and the feedback path for stabilizing the direct current are both used, so that the capacitors and IC pins that were required independently can be shared. The number of pins can be reduced. Also, since the base bias voltage of the input first transistor is supplied by the feedback path, a resistor for applying a bias is not necessary, which reduces the circuit waste current. Further, since the device connected to the input pin of the IC is made into one so that the feedback resistor connected to the base of the first transistor can be built in, unnecessary noise applied to the base of the first transistor is eliminated. Decreases.

Embodiment An embodiment of the present invention will be described in detail with reference to the drawings.

In Fig. 1, Q1 is an input coupling whose base is connected to the input terminal IN on the opposite side via pin P1 of the IC.
A capacitor C1 is connected, a constant current source I1 is connected to the emitter, and a capacitor C2 whose opposite side is grounded is connected via a pin P2. As a result, the transistor Q1 acts as a grounded-emitter amplifier circuit in AC. Further, the collector of the transistor Q1 has its base grounded to the power source Vcc by a capacitor C3 via a pin P3 in an alternating current manner and is connected to the emitter of a base-grounded transistor Q2 having the same polarity as the transistor Q1. It is connected to the resistor R1 which is connected to Vcc,
The transistors Q1 and Q2 form a cascode connection circuit. Resistors R2 and R3 are connected between the base of the transistor Q2 and the power supply Vcc and between the collector and the power supply Vcc, respectively, and the resistance R3 serves as a load resistance of the cascode circuit. Also, the transistor Q3 has its base connected to the emitter of the transistor Q1 and its collector connected to the power supply Vcc.
And a resistor R4 that divides the voltage between Vcc and GND, a diode D1 and a resistor
Differential amplification with transistor Q4 whose base is connected to the connection point of R5, whose collector is connected to the base of transistor Q2, whose emitter is connected to the emitter of transistor Q3, and constant current source I2 which is connected to the common emitter of transistors Q3 and Q4. The circuit is configured. Non-inverting input terminal of A1 is transistor Q2
Is connected to the collector of the
This is a differential amplifier circuit connected to the base of
It is connected to the output terminal OUT via pin P5 of the IC and to the base of transistor Q1 via resistors R6 and R7, and the connection point between resistors R6 and R7 is resistor R8 via pin P4 of the IC. , Capacitor C4 series circuit is grounded.

Next, consider DC operation. Assuming that the potential on the anode side of the diode D1 is Va, the sum of the forward voltage VF of the diode D1 and the VBE of the transistor Q4 and the sum of VBE of the transistors Q1 and Q3 are equal in the balanced state. Q1) is equal to Va. Generally, in order to increase the dynamic range during recording, VB
(Q1) = (1/2) ・ Vcc is often set. Further, the base potential and collector potential of the transistor Q2 are equal, and the output potential V _OUT of the differential amplifier circuit A1 is equal to Va plus the voltage drop across the resistors R6 and R7.

The above is the case where the circuit is in the balanced state, but consider the case where this balance is lost. If the output of the differential amplifier circuit A1 becomes higher than the steady potential for some reason, the base potential of the transistor Q1 also rises, and as a result, the base potential of the transistor Q3 rises.
Since the transistors Q3 and Q4 are differential amplifier circuits, the collector current of the transistor Q4 decreases, the voltage drop of the resistor R2 decreases, the potential of the inverting input terminal of the differential amplifier circuit A1 rises, and the transistor Q2 Raise the base potential. When the base potential of the transistor Q2 rises, the emitter potential also rises, the voltage across the resistor R1 decreases, and the operating current of the transistor Q2 increases. As a result, the voltage drop across the resistor R3 increases and the potential at the non-inverting input terminal of the differential amplifier circuit A1 rises. That is, the potential of the inverting input terminal of the differential amplifier circuit A1 rises, the potential of the non-inverting input terminal drops, and the output potential drops. This serves to pull down the output of the differential amplifier circuit A1 when it becomes higher than the steady potential due to the action of the entire loop.
When the output of the differential amplifier circuit A1 becomes lower than the steady potential, it works to pull it up. After all, the output potential of the differential amplifier circuit A1 is controlled so as to be equal to the voltage drop of Va + R6, R7 which is the steady potential.

Next, looking at the signal flow, the signal applied to the input terminal IN is applied to the base of the transistor Q1 via the capacitor C1 and the pin P1, and the cascode connection circuit consisting of the transistors Q1 and Q2 causes I1R3 / VT It is amplified twice and appears at the collector of transistor Q2. This is a differential amplifier circuit
It is amplified by A1 by a predetermined amplification factor and transmitted to the OUT terminal via pin P5. Further, since the resistor R8 is inserted in series in the capacitor C4 between the pin P4 and the GND in the feedback path, the output signal component is also fed back to the input, thereby performing feedback damping. Since the damping amount can be changed by the resistor R8,
Depending on the type of head connected to the IN pin, it is necessary to adjust the resistance R8 to the optimum value. It is assumed that the impedance of each capacitor is sufficiently small with respect to the signal frequency.

Although this embodiment is a circuit for amplifying a head reproduction signal as in the prior art, the number of capacitors and the number of IC pins are both reduced by one. This is because the conventional circuit is the path of feedback damping Q3 emitter → P4 →
C2 → R6 → P1 → Q1 base and differential amplifier circuit that is a feedback path for DC stabilization A1 output Q4 base → Q8 base → Q9 base →
While the A1 inverting input has an independent path,
In the figure, this was achieved by putting them together, and it was possible to remove the capacitor C5 in Fig. 7. The function of dropping the AC component of the signal of the capacitor C5 and transmitting only the DC component is performed by the capacitor C2 in FIG.

Further, since only one capacitor C11 is required to be connected to the input pin P1 in FIG. 1, there is less influence from the outside due to the pattern, component arrangement, etc. than in the conventional case.

Next, consider the operating currents of the transistors Q1 and Q4. The operating current A (= I1) of the transistor Q1 must be set to a relatively large value of about 1 m to several mA due to restrictions such as the need to use it in the current region where the noise of the transistor or the transistor is the smallest. Since the transistor Q4 does not handle an AC signal and only needs to generate a necessary voltage drop in the resistor R2, the collector current of the transistor Q4 can be suppressed to a small value of 100 uA or less by setting the resistor R2 large.
Therefore, the base current of the transistor Q4 also decreases accordingly, so that the resistors R4 and R5 can be set large and the circuit waste current can be suppressed small.

Further, in this embodiment, the resistor directly connected to the base of the input transistor Q1 is only the resistor R7 corresponding to the resistor R6 in FIG. 7, and there is no resistor corresponding to the resistors R1 and R2 in FIG. Therefore, unnecessary noise mixed in the base of the input transistor Q1 becomes smaller than in the conventional case. Further, the thermal noise generated from the resistors R4 and R5 and the noise generated from the diode D1, the transistors Q3 and Q4, and the constant current source I2 are added to the collector current of the transistor Q4.
Since the base of is grounded AC by the capacitor C3, it is dropped here and does not enter the signal path.

FIG. 2 shows a first other embodiment of the present invention. 2 is different from FIG. 1 in that the diode D1 is a transistor Q5, the differential amplifier circuit A1 is a specific circuit, and the constant current sources I1 and I2 are transistors Q6 to Q8. As shown, the feedback circuit is a resistor from the common collector of the transistors Q11 and Q13 of the differential amplifier circuit A1.
The path is returned to the base of the transistor Q1 via R21, the capacitor C4, and the resistor R20. Also different from FIG. 1 is that a resistor R1 is inserted in series with a diode D1 between the emitter of the transistor Q2 and the power supply Vcc.

According to this embodiment, as in FIG. 1, the number of pins of the capacitor and IC can be reduced as compared with the conventional one, and the resistance R4,
Since the value of R5 can be set to a large value, it is possible to reduce the circuit waste current.

FIG. 3 shows a second other embodiment of the present invention. Transistors Q1 and Q2, resistors R1 to R3, capacitors C1 to
The connection relationship between C3 and the differential amplifier circuit A1 is the same as in Fig. 1,
The description here is omitted. The difference from FIG. 1 is that the base is connected to the emitter of the transistor Q1, the collector is folded back by the current mirror circuit composed of the transistors Q4 and Q5, the collector is connected to the base of the transistor Q2, and the emitter is the reference voltage V1. It has a transistor Q3 connected to. The output of the differential amplifier circuit A1 is connected to the OUT terminal via pin P5 of the IC, the inverting input terminal is connected to the reference potential V2, and the output is a resistor.
It is connected to the non-inverting input terminal of the differential amplifier circuit A2 which is connected to the base of the transistor Q1 via the resistor R8 and the resistor R8 and the capacitor C4, and the pin R4 and the pin P4 of the IC. That is the point.

Considering the DC operation, the base potential VB (Q1) of the transistor Q1 becomes VCC-V1. Also, the transistor Q2
The base potential and collector potential of the differential amplifier A1
The output potential V _{OUT of} is equal to the reference voltage V2. The above is when this circuit is in a balanced state,
Think about when this balance is upset. If the output of the differential amplifier circuit A1 becomes higher than the reference voltage V2 for some reason, the non-inverting input of the differential amplifier circuit A2 becomes higher than the potential of the non-inverting input terminal. The output potential of the differential amplifier circuit A2 rises and the transistor
The base potential of Q1 also rises, and the base potential of transistor Q3 also rises. However, since the emitter potential of the transistor Q3 is constant, the collector current of the transistor Q3 decreases, the currents of the transistors Q4 and Q5 also decrease, the voltage drop of the resistor R2 decreases, and the potential of the inverting input terminal of the differential amplifier circuit A1 decreases. , And the base potential of the transistor Q2,
When the base potential of the transistor Q2 rises, the collector potential drops, so the potential of the non-inverting input terminal of the differential amplifier circuit A1 drops. That is, the potential of the inverting input terminal rises and the potential of the non-inverting input terminal falls, which lowers the output potential of the differential amplifier circuit A1. This is because when the output of the differential amplifier circuit A1 becomes higher than the reference voltage V2, it is lowered by the action of the entire loop. When the output of the differential amplifier circuit A1 becomes lower than the reference voltage V2, the output voltage of the differential amplifier circuit A1 is controlled to be equal to the reference voltage V2 in the end. That is why.

Regarding the signal flow, the first from the IN terminal to the OUT terminal
It is exactly the same as the case of the figure. Regarding the feedback circuit, the output of the differential amplifier circuit A2 is divided by the resistors R6 and R8 and returned to the base of the transistor Q1 via the resistor R7, which performs feedback damping, but the amount of damping is determined by the resistor R8. Can be changed.

Also in this embodiment, it can be seen that the number of capacitors and the number of pins are both reduced by one as compared with FIG. This can be achieved by combining the feedback damping path and the feedback path for DC stabilization, which are independent paths, as in the previous embodiments. Also, only one capacitor C1 is connected to the input pin P1, and the influence from the outside due to the pattern, component arrangement, etc. can be small. Next, transistors Q1, Q3,
Consider the operating currents of Q4 and Q5. Transistor Q1
The operating current of must be set to a relatively large value due to restrictions such as gain and noise, but the transistors Q3, Q4, and Q5 are currents that do not handle AC signals and cause a necessary voltage drop in the resistor R2. Therefore, the collector currents of the transistors Q3, Q4, and Q5 can be kept small. Therefore, a large current is not required to generate the reference voltage V1, and the waste current of the circuit can be kept small. The resistor directly connected to the base of input transistor Q1 is resistor R7.
Therefore, unnecessary noise mixed in the base of the input transistor Q1 is reduced. In addition, the reference voltage
The noise generated from V1 and transistors Q3, Q4, and Q5 rides on the collector current of transistor Q5, but transistor Q2
Since the base of is grounded AC to the capacitor C3, it is dropped here and does not enter the signal path.

FIG. 4 shows a third other embodiment of the present invention. Transistors Q1 and Q2, resistors R1 to R3, capacitors C1 to
The connection relationship between C3 and the differential amplifier circuit A1 is the same as in Fig. 3,
Since the return path is also the same as that in FIG. 3, the description thereof is omitted here. The difference from FIG. 3 is that the base of the transistor Q3 is connected to the emitter of the transistor Q1 and the collector is grounded to GND.
Transistor Q4 whose base is connected to the connection point of resistor R4 and diodes D1 and R5 that divide between GND, and whose collector is connected to the base of transistor Q2
The point is that it is connected to the emitter of.

Considering DC operation, when the potential on the cathode side of the diode D1 is Va, in the balanced state, the forward voltage VF of the diode D1 and the V of the transistors Q1, Q3, Q4 are
Since the sum of BE is 0 (considering the sign), the base potential of the transistor Q1 becomes equal to Va. Further, the base potential and the collector potential of the transistor Q2 are equal, and the output potential V _OUT of the differential amplifier circuit A1 is equal to the reference voltage V1.
The above is when this circuit is in a balanced state. Next, let's think about when this balance is broken. If the output of the differential amplifier circuit A1 becomes higher than the reference voltage V1 for some reason, the differential amplifier circuit A2 has a higher potential at the non-inverting input terminal than at the inverting input terminal. The output potential of the dynamic amplification circuit A2 rises, the base potential of the transistor Q1 also rises, and the base potential of the transistor Q3 also rises. On the other hand, since the base potential of the transistor Q4 is constant regardless of it, the collector currents of the transistors Q3 and Q4 decrease, the voltage drop of the resistor R2 decreases, the potential of the inverting input terminal of the differential amplifier circuit A1 rises, and , The base potential of the transistor Q2 is raised, and the transistor Q2
If the base potential of rises, the collector potential will drop, so
The potential of the non-inverting input terminal of the differential amplifier circuit A1 drops. That is, the potential of the inverting input terminal rises and the potential of the non-inverting input terminal falls, which causes the differential amplifier circuit A1
The output potential of is reduced. Conversely, the differential amplifier circuit A1
When the output of is lower than the reference voltage V1, it works to raise it on the contrary, and eventually the output potential of the differential amplifier circuit A1 is controlled to be equal to the reference voltage V1.

The signal flow is exactly the same as in FIG.

By the way, as mentioned earlier, the only difference from Fig. 3 is the way of connecting the transistors Q3 and Q4.
The same applies to the figure. That is, the number of capacitors and the number of pins are both smaller by one, only one capacitor C1 is connected to the input pin P1, the resistors R4 and R5 can be set large, and the circuit waste current can be kept small. Resistor R4 that reduces unnecessary noise mixed in the base,
Thermal noise generated from R5, diode D1 and transistor Q
3, do not enter the noise signal path generated from Q4, etc.

FIG. 5 shows a fourth embodiment of the present invention. Transistors Q1 and Q2, resistors R1 to R3, capacitors C1 to
The connection relationship between C3 and the differential amplifier circuit A1 is the same as in Fig. 1,
The description here is omitted. The base of the transistor Q3, whose emitter is connected to the emitter of the transistor Q1 and whose collector is connected to the base of the transistor Q2, is connected to the connection point of the resistors R4 and R5 which divide the voltage between Vcc and GND. The output of the differential amplifier circuit A1 is connected to the OUT terminal via the IC pin P5, the inverting terminal is connected to the reference voltage V1, and the output is connected to the resistor R8 and the capacitor C4 via the IC pin P4.
And a resistor R7 to the non-inverting input terminal of the current output type differential amplifier circuit A2 connected to the base of the transistor Q1.

Considering DC operation, assuming that the voltage at the connection point of resistors R4 and R5 is Va, the base-emitter voltages of transistor Q1 and transistor Q3 are almost equal in the balanced state, so the base potential of transistor Q1 is Va. Will be equal. The base potential and collector potential of the transistor Q2 are equal, and the output potential V _OUT of the differential amplifier circuit A1 is the reference voltage.
It is equal to V1. The above is the case when this circuit is in a balanced state, but consider the case when this balance is lost. If the output of the differential amplifier circuit A1 becomes higher than the reference voltage V1 for some reason, the non-inverting input terminal of the differential amplifier circuit A2 becomes higher than the potential of the inverting input terminal. Therefore, the output current of the differential amplifier circuit A2 increases and the base potential of the transistor Q1 increases. On the other hand, the transistors Q1 and Q4 are a differential amplifier circuit in terms of direct current, so if the base potential of the transistor Q1 rises, the collector current of the transistor Q3 will decrease and the voltage drop of the resistor R2 will decrease. When the potential of the inverting input terminal of the circuit A1 is raised and the base potential of the transistor Q2 is raised and the base potential of the transistor Q2 rises, the collector potential drops, so the differential amplifier circuit A1
The potential of the non-inverting input terminal of is lowered. That is, the potential of the inverting input terminal rises and the potential of the non-inverting input terminal falls, which lowers the output potential of the differential amplifier circuit A1. On the contrary, when the output of the differential amplifier circuit A1 becomes lower than the reference voltage V1, it works to raise it on the contrary, and eventually the output potential of the differential amplifier circuit A1 is controlled to be equal to the reference voltage V1. It has been done.
When the polarity of transistor Q3 is opposite to that of transistor Q1, the emitter and base of transistor Q3 remain the same and the collector is folded back with a newly provided current mirror to connect to the base of transistor Q2. The inverting input and the non-inverting input terminal of circuit A2 should be exchanged (however, VB (Q1) becomes 2 * V BE (about 1.4V) higher than Va).

Regarding the signal flow, the first from the IN terminal to the OUT terminal
It is exactly the same as the case of the figure. Regarding the feedback circuit, the current output of the differential amplifier circuit A2 is converted to the R7 voltage and returned to the base of the transistor Q1 via the resistor R6, which performs feedback damping, but the damping amount can be changed by the resistor R7. You can

In this embodiment, the number of capacitors and the number of pins are both reduced by one, as in the case of FIG. This can be achieved by combining the feedback damping path and the feedback path for DC stabilization into one. Also, only one capacitor C1 is connected to the input pin P1, and the influence from the outside due to the pattern, component arrangement, etc. can be small.

Next, considering the operating currents of the transistors Q1 and Q3, the operating current of the transistor Q1 must be set to a relatively large value due to restrictions such as gain and noise, but the transistor Q3 does not handle AC signals. Since it is enough that there is enough current to cause the required voltage drop in the resistor R2,
The collector current of Q3 can be kept small. Although the transistors Q1 and Q3 are symmetrical in terms of a circuit diagram, actually, the emitter area of the transistor Q1 is set to be several tens to several hundred times larger than that of the transistor Q3 in terms of noise and input capacitance.
Also, by setting the constants of resistors R1 to R3, the current
The collector current of Q1 is several tens of times that of the transistor Q3. Therefore, the base current of the transistor Q4 also decreases accordingly, so that the resistors R4 and R5 can be set large and the circuit waste current can be suppressed small.

Since the resistor R6 is the only resistor directly connected to the input and the base of the transistor, unnecessary noise mixed in the base of the input transistor is reduced. Furthermore, the thermal noise generated from the resistors R4 and R5 and the noise generated from the transistor Q3 are carried on the collector current of this, but they are dropped here because the base of the transistor Q2 is AC grounded. Don't get in the way.

FIG. 6 shows a fifth other embodiment of the present invention.

FIG. 6 shows the differential amplifier circuit A1 of FIG. 5 with transistors Q7 to Q2.
2 and resistors R9 to R18, and without the equivalent of the differential amplifier circuit A2, simply resistors R22 to R24 and capacitors
The feedback circuit is composed of the passive element of C4. The Darlington-connected transistors Q2 and Q3 in FIG. 6 correspond to the transistor Q2 in FIG.

As in the case of FIG. 5, this embodiment is also characterized in that the number of pins of the capacitor and the IC can be reduced and the values of the resistors R4 and R5 can be set large, so that the waste current of the circuit can be reduced.

[Advantages of the Invention] As described above, according to the amplifier circuit of the present invention, in addition to reducing the number of capacitors and pins of the IC,
The number of elements connected to the input pins of the IC can be reduced, making it less susceptible to external influences. Further, since the current of the constant current source flowing through the input transistor can be reduced, the circuit waste current can be reduced and the noise directly applied to the input can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIGS. 2 to 6 are circuit diagrams showing other embodiments of the second to sixth embodiments of the present invention, and FIG. 7 is a conventional circuit diagram. Is. Q1, Q2 ...... Transistors R1 to R3 ...... Resistors A1 ...... Differential amplifier circuit Q3, Q4 ...... Differential amplifier circuit R6 to R8, C4 ...... Feedback circuit

Claims (5)

[Claims] 1. A first transistor whose emitter is grounded via a first capacitor and a transistor whose cascode connection is made to this first transistor and whose base is grounded via a second capacitor have the same polarity. A second transistor, a first resistor connected between the emitter of the second transistor and the first reference potential, and a connection between the base of the second transistor and the first reference potential. The second resistor, the third resistor connected between the collector of the second transistor and the first reference potential, and the emitter of the first transistor connected to one input,
The other input is connected to the second reference potential and the output is connected to the second reference potential.
A voltage detection circuit connected to the base of the transistor and one input to the base of the second transistor,
A first differential amplifier circuit having the other input connected to the collector of the second transistor, and a feedback circuit for feeding back the output of the differential amplifier circuit to the base of the first transistor, which are connected in series. A feedback circuit having a fourth resistor and a fifth resistor, and a connection point between the fourth resistor and the fifth resistor is grounded via a sixth resistor and a capacitor. An amplifier circuit characterized by. 2. A voltage detection circuit having a second input having one input connected to the emitter of a first transistor, the other input connected to a second reference potential, and the output connected to the base of a second transistor. The amplifier circuit according to claim 1, wherein the amplifier circuit comprises a differential amplifier circuit. 3. The voltage detection circuit comprises a third transistor having a base connected to the emitter of the first transistor, an emitter connected to the first reference potential, and a collector connected to the base of the second transistor. The amplifier circuit according to claim 1, wherein: 4. The voltage detection circuit has a fourth transistor having a base connected to the emitter of the first transistor, a base connected to a second reference potential, and an emitter connected to the emitter of the fourth transistor, The amplifier circuit according to claim 1, wherein the amplifier circuit is configured by a fifth transistor having a polarity opposite to that of the fourth transistor whose collector is connected to the base of the second transistor. 5. The voltage detection circuit is composed of a sixth transistor whose emitter is connected to the emitter of the first transistor, whose base is connected to the second reference potential, and whose collector is connected to the base of the second transistor. The amplifier circuit according to claim 1, wherein: