JPS6228885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an integrated amplifier circuit for a preamplification system or an output amplification system used in the audio band.
In particular, the present invention relates to an amplifier circuit in which one external terminal is shared for improving the suppression ratio of power supply ripples and for cutting off audio output.

When integrating amplifiers and the like, increasing functionality and reducing the number of external terminals are contradictory demands. FIG. 1 shows an example of a circuit of an audio band output amplifier constructed with a minimum number of external terminals and external components, in which an audio signal IN supplied to input terminal A is amplified and output to terminal D. E is the power supply terminal, C is the ground terminal, and between terminals D and C, connect a capacitor C ₂ for DC cutoff and a load R _L (for example, a speaker).
is connected externally. B is also an external terminal,
A capacitor _C1 is externally connected here, which has the function of grounding the terminal B in an alternating current manner and suppressing power supply ripples. R ₁ to R ₄ are resistors, Q ₁ to _{Q 3} are transistors, V _B is a constant voltage source, and A ₁ is an amplifier, which are integrated within the IC chip. The input IN from the terminal A is superimposed on a constant value bias voltage V _B and applied to the + side input of the amplifier _A1 . A part of the output of amplifier A ₁ is fed back to the negative input through feedback resistor R ₄ , and between this negative terminal and terminal B, resistor R ₃ is connected along with resistor R ₄ to determine the amount of feedback. . A resistor R ₂ connected between terminals E and C and a diode-connected transistor Q ₁ ,
Q ₂ and a transistor Q ₃ whose base input voltage is the voltage V _BE of Q ₂ constitute a constant current source, and the potential of the output terminal D is determined by this and resistors R ₃ and R ₄ .

In other words, although not shown in this circuit, the output stage of amplifier _A1 is push-pull, and since it operates with a single power supply, the output is taken from terminal D and ground C, and if this is done, the DC potential of terminal D will be Since it is undefined, the potential of terminal D is determined through the path of feedback circuits R ₃ , R ₄ and transistor Q ₃ . Now, transistors Q ₁ to _{Q 3} have the same shape and have the same base-to-emitter voltage V _BE , and V _B
= V _BE and further assuming that the input bias current of amplifier A ₁ is small and the offset voltage is zero, the potentials of the + and - terminals of amplifier A ₁ are equal, so the DC output potential of terminal D is V ₀ is a value obtained by adding the voltage drop caused by the resistor R ₄ to the potential V _B of the negative terminal. Here, the current I ₄ flowing through the resistors R ₄ and R ₃ and the transistor Q ₃ is equal to the current flowing through the resistor R ₂ and the transistors Q ₁ and Q ₂ , so the DC output potential V ₀ of the terminal D is V ₀ = V _B +R ₄ ·I ₄ =V _BE +R ₄ ·(V _CC −2V _BE )/R ₂ =R ₄ /R ₂ V _CC +(1−2R ₄ /R ₂ )V _BE . Therefore, if R ₄ /R ₂ = 1/2, then V ₀ =V _CC /2, so the output drive of amplifier _A1 is on the V _CC side.
If the saturation conditions are similar on the GND side, the output waveform will saturate symmetrically in positive and negative directions, and will be optimally controlled by following power fluctuations.

On the other hand, if the amplifier A ₁ has sufficient gain, the overall gain A _V is determined by the feedback circuit and is given by A _V =1+R ₄ /R ₃ .

By the way, when a ripple voltage is superimposed on the DC power supply V _CC , the change first appears as a change in the current value of the constant current source consisting of resistor R ₂ and transistors Q ₁ to Q ₃ , which is bypassed by capacitor C ₁ . (smoothed), but some appears as a potential change at terminal B. In particular, if the ripple voltage has a low frequency, the bypass effect of the capacitor _C1 cannot be expected, and the ripple voltage will appear at the output terminal D through the resistors _R3 and _R4 (multiplied by _R4 / _R3 ). In order to improve this point, there is a method of adding an external capacitor to the collector terminal of the transistor Q ₁ and forming a smoothing circuit together with the resistor R ₂ to reduce the power supply ripple appearing at the terminal B. This requires an external terminal for external connection, and since this is only intended to improve the ripple suppression rate, it is not desirable for ICs that require a reduction in the number of pins.

In general, the number of external pins required for ICs tends to increase as ICs become more multi-functional and highly integrated, but there are restrictions on the number of pins due to the size of the IC, and since packages are standardized, an increase of 1 pin is 2 to 2. This will require the next grade package with more 3 pins. Therefore, even if an external terminal is used to improve the ripple suppression rate, it is desirable that the terminal be used for other purposes as well. Terminals also include those that are always used, such as power supply terminals, and those that are used temporarily, such as certain signal input/output terminals.
There are various types, such as when one is used, the other is always in a dormant state. Particularly in the latter case, it is conceivable that one terminal can be used for both.

The present invention has been made from this point of view, and includes an amplifier circuit that integrates a circuit for amplifying audio input, in which a power supply ripple suppression circuit and an audio cutoff circuit that operates with a DC control voltage are provided in the circuit within the chip. The chip is also characterized in that a terminal for externally attaching components is provided, and a capacitor of the power supply ripple suppression circuit is externally attached to the chip, and an input end of the audio cutoff circuit is connected to the terminal. This will be explained in detail with reference to.

FIG. 2 is a circuit diagram showing an embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. This circuit is obtained by adding a power supply ripple suppression circuit 10 to the circuit shown in FIG. 1, and adding a terminal F externally to which a ripple improvement capacitor _C3 is connected externally. Note that the base of a transistor _Q9 for output cutoff is connected to this terminal F as shown in Figure 3b, and a DC control voltage is applied to terminal F to turn on the transistor _Q9 , making it possible to cut off the output. That's what I do. The suppression circuit 10 is a transistor _Q4
A pair of pnp transistors consisting of ~Q ₇ , diode Q ₈ and resistors R ₅ ~R ₇ , whose bases are connected together.
Q ₅ , Q ₆ and the npn transistor pair Q ₄ , Q ₇ have the same dimensions, and R ₅ =R ₇ . The series circuit consisting of transistors Q ₅ , Q ₄ and resistor R ₅ is simply connected in series between the power supply V _CC and earth GND, but the series circuit consisting of transistors Q ₆ , Q ₇ and resistor R ₇ in parallel is connected in series between the power supply V CC and earth GND. In the circuit, the connection point (collector) of transistors Q ₆ and Q ₇ is connected to terminal B. The bases of transistors Q ₅ and Q ₆ are commonly connected to the collector of transistor Q ₅ ,
Further, the bases of transistors Q ₄ and Q ₇ are commonly connected to the base of transistor Q ₃ and both receive the same base voltage. This connection allows the transistor to
Collector current of Q ₅ , Q ₆ and transistors Q ₄ , Q ₇
Since the collector currents of are equal and the collector currents of Q ₅ and Q ₄ are the same, the collector current I ₂ of Q ₆ is equal to the collector current I ₁ of Q ₅ and Q ₄ ,
Furthermore, it is also equal to the collector current _I3 of _Q7 .
In other words, the collector current _I2 of transistor _Q6 is at terminal B
The potential at terminal B is not influenced by currents I ₂ and I ₃ and therefore by the suppression circuit 10, since the current I ₃ which appears to flow into but is equal to it is absorbed through transistor Q ₇ .

On the other hand, if there is a ripple component in the power supply V _CC , the base potential of transistors Q ₂ , Q ₃ , etc. will vary slightly accordingly, the collector current of transistor Q ₃ will fluctuate, and terminal B will have a voltage corresponding to the ripple component. Fluctuations are about to occur, but for this voltage fluctuation,
Capacitor C ₃ connected between terminal F and earth, and resistor R ₆ connected between terminal F and the emitter of transistor Q ₄ and the anode of diode D ₈
acts as a suppressor. That is, when current _I4 flows through transistor _Q3 due to the ripple component, the collector current of transistor _Q4 also increases. That is, Q ₂ ,
When the base voltage of Q ₃ ... increases, the base of Q ₄ ,
The base current of Q ₄ increases through the path of the emitter, resistor R ₅ or R ₆ , and capacitor C ₃ , which causes an increase in the collector current of Q ₄ . If this increment is I ₁ ', an equal amount of current I ₂ ' (an increment in current I ₂ ) also flows out from the collector of transistor Q ₆ . However, in transistor Q ₇ , as the base potential increases, the base current increases slightly through the path between the Q ₇ base, its emitter, and resistor R ₇ , but unlike Q ₄ , there is no path passing through R ₆ and C ₃ , so the base current increases. remains very small (originally
R ₅ and R ₇ have a negative feedback function), so the collector current of Q ₇ remains almost the same as I ₃ . Therefore, the increased collector current _I'2 of transistor _Q6 flows into point B. This is in reverse phase with the current I ₄ , so the resistance
If the value of R ₆ is set and |I′ ₂ |= |I ₄ |, then the current I′ ₂
and I ₄ are canceled out at terminal B, and fluctuations in terminal voltage due to ripples are suppressed. When the ripple has the opposite polarity, the polarity of I ₄ is reversed (Q ₃ collector current decreases) I′ ₁ , I′ ₂
is also opposite polarity, that is, I ₁ and I ₂ decrease (in this case, Q ₄
In addition to the base potential drop of C _{3 ,} a discharge passes through R ₆ and R ₅ of C 3 and drives Q ₄ in the off direction), and in addition to the base potential drop, the collector current of _{Q 7} also
It decreases because there is a discharge passing through R ₆ , Q ₈ , and R ₇ , but
The degree of this is not as significant as Q ₄ because of the voltage drop in Q ₈ . This results in a decrease in the collector current of _Q3 .
The differential absorption of I ₂ and I ₃ from the terminal B circuit by Q ₇ compensates and prevents ripple voltage from appearing at terminal B.

The above-mentioned amplifier circuit has only a terminal F added externally, and if a capacitor _C3 is externally attached to this, the ripple suppression ratio can be improved. On the other hand, if a constant DC potential is applied to terminal F, Q ₄ , Q ₇
It is the same as if the suppression circuit 10 were not provided, and the whole becomes equivalent to that shown in FIG. By adding a circuit as shown in FIG. 3, terminal F can also be used for the audio output cutoff function. Figure a shows an example of a circuit that applies a DC potential V _S to the terminal F. When the switch SW is turned on, the terminal F becomes V _S through the resistor R, and the transistor shown in Figure 2
The emitter potentials of Q ₄ and Q ₇ both rise and transistors Q ₄ to Q ₇ are all turned off. FIG. 2B shows an example of the audio cutoff circuit 20 added to the circuit shown in FIG. The circuit 20 includes a resistor _R8 (optional) inserted between the terminal A and the constant voltage source _VB , and this resistor.
It consists of a transistor Q ₉ which grounds the output side of R ₈ and its base resistor R _9. When the switch SW is closed and the terminal F is set to a DC potential V _S , the transistor Q ₉
turns on and draws the audio input IN from terminal A to ground. Therefore, audio output from output terminal D is cut off. On the other hand, if the switch SW is opened, transistor _Q9 is turned off, so the audio input IN
is guided to the amplifier _A1 , and at the same time the suppression circuit 10 of FIG. 2 becomes operational.

Figure 4 shows another example of the connection of transistors Q ₁ to _{Q 7} , where a shows resistors R ₁₀ and R ₁₁ are also inserted into the emitters of transistors Q ₂ and Q ₃ , and b shows the transistor
_Q1 used without diode connection (resistance
( _R10 can be omitted) Instead of using the diode _Q8 , the resistor _R'5 is used as the emitter of the transistors _Q4 and _Q7 .
This is a parallel series series-parallel circuit consisting of R′ ₇ and R ₁₂ .

As described above, according to the present invention, one external terminal of an integrated circuit for amplifying an audio signal can be connected to
Since it can be used for both audio isolation and improvement of the ripple suppression ratio, it has the advantage of minimizing the increase in the number of external terminals that accompanies the multifunctionalization of IC chips.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional output amplifier used in the audio band, Figure 2 is a circuit diagram showing an embodiment of the present invention, and Figures 3a and b are the amplifier circuits in Figure 2 with an audio cutoff function. FIGS. 4a to 4c are main part circuit diagrams showing a modification of FIG. 2. In the figure, 10 is a power supply ripple suppression circuit, 20 is an audio cutoff circuit, F is an external terminal for control, and _C3 is a ripple improvement capacitor.

Claims (1)

[Claims] 1. An audio signal is input to one input terminal, and a feedback resistor R ₃ , R ₄ circuit is connected to the other input terminal, and a direct current according to the power supply voltage flows through the feedback resistor circuit. In the integrated amplifier circuit, in which the output terminal D is set to a desired potential, there is a terminal F to which a DC control voltage is applied or an AC ground is applied, and when a DC control voltage is applied to the terminal F, an audio signal line is connected to the terminal F. an audio cutoff circuit 20 that turns on the connected transistor _Q9 and drops the audio signal to the ground to eliminate the audio output; and a first and second circuit connected in series between the power supply and the ground.
transistors Q ₅ and Q ₄ and a resistor R ₅ and third and fourth transistors Q ₆ and Q ₇ and a resistor R ₇ , and the first and third transistors Q ₅ and Q ₆ are connected to a current mirror. , second and fourth transistors Q ₄ ,
Q ₇ is also connected to the current mirror, the series connection point of the third and fourth transistors is connected to the feedback resistor circuit, and the series connection point of the second transistor Q ₄ and resistor R ₅ is connected to the terminal F. , a circuit 10 that suppresses fluctuations in the potential of the output terminal D due to power supply ripples by grounding the terminal F in an alternating current manner.
An amplifier circuit comprising: