JPS61145909A - Low frequency amplifier - Google Patents

Abstract

PURPOSE:To set a collector current of an output stage transistor (TR) in matching with each load condition by having only to switch one switch to changeover the operation of both a phase inverting circuit and a bias current switch circuit. CONSTITUTION:In closing a switch 4, an interlocked switch 8 is opened, the same input signal is fed to input terminals 1, 2 via a switch 9 to invert the phase inverting circuit, a signal having an opposite phase to that of an input signal is fed to a low frequency amplifier circuit 7 to allow low frequency amplifier circuits 6, 7 to BTL-drive a speaker 10. In opening the switch 4, the switch 8 is closed, a different input signal is fed to the input terminals 1, 2 by the switch 9 to bring the phase inverting circuit 3 to the noninverting state, a signal in phase to that of the input signal is fed to the low frequency amplifier circuit 7, the low frequency amplifier circuits 6, 7 drive separately a headphone load 11. In order to set the output stage bias current to a proper value, a value of a resistor 143 is changed normally to change the bias state.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a low frequency amplifier used in electronic equipment such as radio receivers.

BACKGROUND OF THE INVENTION FIG. 4 is a block diagram of a conventional low frequency amplifier having a phase inversion circuit and peripheral circuits. In Figure 4, 1
．． 2 is an input terminal, 3 is a phase inversion circuit, 4 is a changeover switch, 6 and 7 are low frequency amplifier circuits, 8°9 is a load switching switch, 10 is a speaker linked to switch 4,
11 is a headphone.

The operation of the conventional low frequency amplifier shown in FIG. 4 will be explained below. When the left and right channels of the headphones 11 are to be driven separately by the input signal applied to the input terminal 1.2, the low frequency amplifier circuit 6.
The outputs of 7 are connected to headphones 11, respectively. In this case, the switch 4 is connected to the side where the input signal applied to the input terminal 1 and the output of the phase inversion circuit 3 applied to the low frequency amplifier circuit 7 are in phase. The same human input signal is applied to the input terminals 1.2, and the speaker 10 is connected to BTL (Ba1ance).
d Transformer La5s) When driving, open switch 8, switch 9 to the speaker side, and switch 4 connects the input signal applied to input terminal 1 and the output of phase inversion circuit 3 applied to low frequency amplifier circuit 7. is connected to the opposite phase side, and the low frequency amplification circuits 6 and 7 amplify the signals of opposite phase to each other, and the speaker 10 is connected to the BT side.
Drive L.

Problems to be Solved by the Invention However, in the conventional circuit configuration described above, at least one circuit with two contacts is required for the switch used to switch the phase inversion circuit, and the increase in the size of the components makes it difficult to downsize the entire low frequency amplifier. was prevented. Also, such a low frequency amplifier is
Normally, it is used as a B slow operation from the viewpoint of current saving and high efficiency, but in this case, crossover distortion caused by nonlinearity of the voltage between the base and emitter of the transistor and the collector current characteristics becomes a problem. Therefore, the operating point of the transistor when no signal is present must be set in a state where its nonlinearity is not a problem, and a bias current flows even when there is no signal.

The larger the output load and load current, the more linear the operating point when there is no signal must be used, and as a result, the bias current when there is no signal increases. When using speakers and headphones as a load for a low-frequency amplifier, the bias state when there is no signal must be set so that distortion does not become a problem when using a larger speaker as the load. Even though there are times when there is no problem in setting the bias current to a lower level, the low frequency amplifier must be operated with the settings corresponding to the speaker. This is a means of solving a major problem in terms of current savings due to the miniaturization of batteries that accompany the miniaturization of devices.In order to solve the above problems, the present invention provides an output signal that is in phase with the input signal. A phase switching circuit that performs phase switching by switching current supply to a first differential amplifier circuit that generates a signal and a second differential amplifier circuit that generates an output signal that is in opposite phase to the input signal by opening and closing a switch; The special features include a bias switching circuit consisting of a first current supply circuit that operates simultaneously with the first differential amplifier circuit and a second current supply circuit that operates simultaneously with the second differential amplifier circuit. It is something that

Operation The low frequency amplifier circuit of the present invention allows the operation of the phase inversion circuit to be changed simply by opening and closing a switch, and also uses a bias switching circuit that switches in conjunction with this to increase the bias current when driving speakers, and to increase the bias current when driving headphones. It is possible to reduce the bias current,
This makes it possible to reduce the size of the required switch and save current by adjusting the bias appropriately.

Embodiment FIG. 1 is a block diagram of a low frequency amplifier and peripheral circuits in an embodiment of the present invention, and FIG. 2 is a circuit diagram of a specific example thereof.

In FIG. 2, 5 is a phase inversion and bias switching circuit;
6 and 7 are low frequency amplification circuits, and the circuit configuration 70 is exactly the same as that of 6. Phase inversion and bias current switching circuit 1
3, transistor 116 and transistor 117
constitutes a first differential amplifier circuit, transistor 124 and transistor 125 constitute a second differential amplifier circuit, and the collector of transistor 116 and transistor 12 constitute
6, the collector of transistor 117, and the collector of transistor 124 are connected to each other. Transistor 107 supplies current to the first differential amplifier circuit, and transistor 111 supplies current to the second differential amplifier circuit. Transistors 119 and 120 are common active loads for the first and second differential amplifier circuits. transistor 1
06°106.107.108 and transistor 1o
9°110, 111, and 112 constitute a current mirror circuit, respectively. Also, the transistor 121°12
6, 127 and transistors 129 and 130 each constitute a current mirror circuit, and the constant current source 1
Supply a current equal to 38 currents.

The transistor 113 performs a switching operation by opening and closing the switch 4. Resistance 114, 115° 122112
3.118 is for controlling the gains of the first and second differential amplifier circuits, and sets the absolute value of the gains of the first and second differential amplifier circuits to 1. Resistance 100, 102, 1
03.104 is for bias. Capacitor 101 is for ripple removal. The input signal is passed from terminal 164 to transistors 116 and 122 via capacitor 163.
0 base, and the output signal is taken out from the collectors of transistors 117 and 124 via capacitor 128 and input to low frequency amplifier circuit 6.

In the low frequency amplifier circuit 7, the resistors 143 and 146°14
8 diode 147 and transistors 141 and 142 constitute an output stage bias circuit, and current is supplied to resistor 143 from transistors 106 and 110 of phase inversion circuit 3. The low frequency amplification circuit 7 has exactly the same configuration as the low frequency amplification circuit 6, and current is supplied to the resistor of the low frequency amplification circuit 7 corresponding to the resistor 143 by the transistors 105 and 109 of the phase inversion circuit 3.

Circuit blocks 5.6.7 in FIG. 2 correspond to 5 and 6.7 in FIG. 1, respectively.

Further, switches 4.8.9 in FIG. 2 correspond to switches 4 and 8.9 in FIGS. 1 and 4, respectively, and these switches are switched in conjunction with each other.

First, the phase inversion circuit will be explained. fJ', In Figure 2, when switch 4 is closed, transistors 113, 105, 106, 107, and 108 enter the cutoff region because their bases and emitters are shorted, and no collector current flows through these transistors. . Since the collector current of transistor 107 does not flow, transistor 11
The tenth differential amplifier circuit consisting of 6 and 117 does not operate. The transistors 121, 126, and 127 are current mirror circuits, and the transistor 121 has a current source 138.
However, since transistor 10 does not operate, power is supplied through switch 4. A current equal to that of the constant current source 138 flows through the transistor 126, but since the transistor 113 is in a cut-off state, power is supplied from the transistor 112. Furthermore, since the transistors 1Q9.11o, 111, and 112 constitute a current mirror circuit, the collector currents of these transistors are all equal to the current I of the constant current source 138. , therefore, the second differential amplifier circuit constituted by transistors 124 and 125 supplied with current by transistor 111 will operate. In this case, the input signal applied to the input terminal 1 is amplified by the second differential amplifier circuit, becomes an inverted output from the collector of the transistor 124, and is input to the low frequency amplifier circuit 7. If open, transistor 10
5, 106, 107, and 108 constitute a current mirror circuit, and since the collector current of transistor 108 is equal to the collector current of transistor 121, the collector current of transistor 108 is equal to the constant current source current, and transistor 107 Electrical current also flows through the collector of
As a result, the first differential amplifier circuit composed of transistors 106 and 107 operates. On the other hand, transistor 1
Current I also flows through the collector of transistor 126, but when switch 4 is opened, transistor 113 forms a current mirror circuit with transistor 108, so the collector current of the transistor also becomes a current, supplying current to the collector of transistor 126. do.

Therefore, the collector current of transistor 112 does not flow.
The collector currents of transistors 109, 110, and 111 that constitute a current mirror circuit with transistor 112 also stop flowing. Therefore, the second differential amplifier circuit including transistors 124 and 125 to which current is supplied by transistor 111 does not operate. In this case, the input signal applied to the input terminal 1 is amplified by the first differential amplifier circuit, becomes a non-inverted output from the collector of the transistor 117, and is input to the low frequency amplifier circuit. When the switch 4 is closed by the above operation, the switch 8 linked to it is opened, the switch 9 is connected to the contact a side, and the same human input signal is applied to the input terminals 1 and 2, and the phase inversion circuit 3 is inverted. By operating the low-frequency amplifier circuit 7 and applying a signal having an opposite phase to the input signal to the low-frequency amplifier circuit 7, the speaker 10 is driven by the low-frequency amplifier circuits 6 and 7 in a BTL manner. When the switch 4 is opened, the switch 8 is closed, the switch 9 is connected to the contact side, and separate input signals are applied to the input terminals 1 and 2, and the phase inversion circuit 3 is in non-inversion operation, and the low frequency amplification circuit is By adding a signal in phase with the input signal to 6.7, the low frequency amplification circuit 6.
7 separately drive the headphone load 11.

Next, the bias current switching circuit will be explained.

In the low frequency amplifier circuit 7 of FIG. 2, the base-emitter voltage of the output circuit transistors 144 and 146 is given by the following equation.

V""144= (vD147 + V"142) -
(vat, 45+ VR,',) (11Vat0.=
(Tax144+Vn,, ) -(To, 47
+vBx, 42) f21 where VBx142: Transistor 1420 base
Emitter-emitter voltage VBII+44: Base-emitter-edge voltage of transistor 144 vBE145: Base-emitter-edge voltage Vo 1 of transistor 1450
47: Forward voltage drop VR of diode 147
143: Voltage sieve across resistor 143. Therefore, in DC operating condition, output transistor 151
．． 152 collector currents are equal, and formula (1) and (2
) The transistors 144 and 146 operate in a state that satisfies the equation. In order to set the output stage current (Iasumi current) to an appropriate value, the bias state is changed by changing the value of the normal resistor 143 and by changing the value of VR12,'l in equations (1) and (8). let

Separately, it is also possible to change the current state by changing the current value flowing to operate the resistor 143, transistor 142, and drive transistor 141, and changing the voltage drop VR143 across the resistor 143. It is. In FIG. 2, the collectors of the transistors 106 and 110 of the phase inversion circuit 3 are connected to the bases of the resistor 143 and the transistor 142 of the low frequency amplifier circuit 7, and the resistor 1 of the low frequency amplifier circuit 6 is
The collectors of transistors 106 and 109 of the phase inversion circuit 3 are connected to the portion corresponding to 43. As mentioned above, in the phase inversion circuit 3, the transistor 10
51106, 107.108 constitute a current mirror circuit, and transistors 109.110, 111.1
12 also constitutes a current mirror circuit. Therefore, when switch 4 is closed, transistors 109, 110, 1
Since only the 11°112 current mirror circuit operates,
A transistor 110 is connected to the resistor 143 of the low frequency amplifier circuit 7.
In addition, a current is supplied to a portion of the low frequency amplifier circuit 6 corresponding to the resistor 143 by the transistor 109. When switch 4 is open, transistor 105,1
Since only the current mirror circuits 06, 107, and 108 operate, current is supplied to the resistor 143 of the low frequency amplifier circuit 7 by the transistor 106, and to the corresponding portion of the low frequency amplifier circuit 6 by the transistor 106.

Here, transistor 1 of transistors 106, 106
The emitter area ratio or the number of parallel connections to 08,
By changing the emitter area ratio of the transistors 109 and 110 to the transistor 112 or the number of parallel connections, the low frequency amplifier circuit 7 can be operated by switching the switch 4.
The current value supplied to the resistor 143 and the corresponding resistor of the low frequency amplifier circuit 6 changes, and as a result, the bias current R of the output stage also changes. As mentioned above, when using speakers as a load, the load is heavier than when using headphones as a load, and the range of change in output current relative to output voltage becomes wider. Therefore, in order to eliminate crossover distortion, it is necessary to The operating point of the transistor must be set in a region where the base-emitter voltage vs. collector current characteristics are closer to linear. In other words, it is necessary to increase the collector current (bias current) of the output stage transistor when there is no signal.

Therefore, when the switch 4 is first closed to drive the speaker BTL, the transistors 109 and 110 and the transistor 112 have the same characteristics, and the transistor 109 and the transistor 112 have the same characteristics.
, 110, and set the values of the resistors corresponding to the resistor 143 of the low frequency amplifying section 7 and the resistor 143 of the low frequency amplifying section 6 to a state that does not cause crossover distortion when driving the speaker. Once the operating point has been determined to the set value, then with switch 4 open,
In order to avoid crossover distortion when driving a headphone load, the output stage transistor 15 is smaller than when driving a speaker.
The collector current values of the transistors 106 and 106 are set so as to reduce the collector current during no signal of 1,152. In this case, in order to increase the voltage drop across the resistor 143 of the low frequency amplifier circuit 7 and the corresponding resistor of the low frequency amplifier circuit 6, the collector currents of the transistors 105 and 106 are lower than the collector currents of the transistors 109 and 110. must also be made larger. (In the example, the output stage transistor 15 is increased by about 50 μA.
1,152 collector current decreases by about 51 nk) This can be done by changing the emitter area ratio of transistors 105 and 106 with respect to transistor 108 as described above, or by connecting multiple devices in parallel if the same element is used. This can be handled by changing the current/to-mirror ratio. Further, as a means for changing the mirror ratio, an appropriate resistor may be inserted between the emitter of each transistor and the power supply line 170. Furthermore, in this embodiment, only the bias current switching of the low frequency amplifier circuit is performed, but the transistors 105, 106, 107, and 108 of the current mirror circuit, the transistors whose bases and emitters are connected to each other, and the transistor 109 ,11
0,111.112 current mirror circuit and a transistor whose base and emitter are connected to each other, the current of the other circuit can be switched, or only one side can be used to switch the other circuit to either state. It is also possible to apply it in such a way that it operates only in

By using a jack as shown in FIG. 3, each switch in this embodiment can have all opening/closing functions i+ and va added by inserting and removing a plug.

The terminal 21 in FIG. 1 is replaced by the switch 8 in FIGS. 1 and 2.
, terminals 22, 23 are connected to switch 9 of FIGS. 1 and 2.
, terminals 24 and 25 are connected to switch 4 in FIGS. 1 and 2.
The operation of the jack shown in FIG. 3, which corresponds to the above, will be explained with reference to FIG. 1.

When the plug is not inserted, the terminal 23 in FIG. 3 is the speaker side terminal of the switch 9 in FIG. is connected to. Terminal 24 is connected to the power supply voltage,
The terminal 25 is a terminal on the side of the phase inversion circuit 3 and the bias current switching circuit 12 of the switch 4 in FIG. When the plug is inserted, the terminal 21 contacts the terminal 17 of the plug as shown in Figure 3, the switch 8 in Figure 1 is closed and connected to the radon, and the terminals 23 and 24 are open. Then, the terminal 24 comes into contact with the terminal 18 of the plaque, and the switch 9 in FIG. 1 is connected to the headphone side. Also,
Since the terminal 19 of the plug presses down the insulating pad 20, the terminals 24, 25 of the jack are opened, and the switch 4 of FIG. 1 is in the open state, and the phase inverting circuit 3 is in a non-inverting operation.

Note that the diode 1 in the low frequency amplifier circuit 7 in FIG.
When the circuit of this embodiment is integrated into an IC, 47 is used as a diode with the collector and base of the transistor short-circuited. Furthermore, the configuration of the first stage amplifier circuit configured by the transistors 131, 133, 134, 135, 136, and resistors 132, 137 in the low frequency amplifier circuit 7 is not limited to this. The output circuit is not limited to this either.

For the phase inversion and bias current switching circuit 6, the input may be applied to the base side of the transistors 117, 125. However, in this case, the output phase will be reversed, so change the output load connection as necessary. Also, the collectors of transistors 116 and 126 or transistor 1
It is sufficient that at least one of the collectors 17 and 124 is connected to each other, and the collector load is not limited to the active load of this embodiment.

Effects of the Invention As described above, the low frequency amplifier of the present invention can switch the operation of both the phase inversion circuit and the bias current switching circuit by simply opening and closing one switch, and can switch between two sets of low frequency amplifier circuits. It is possible to save current by setting the collector current (bias current) of the output stage transistor according to the load conditions when driving the used speaker BTL and when driving the headphone load separately. Since the switch configuration can be changed from the conventional one circuit and two contacts to one circuit and one contact, it is possible to simplify the switch, downsize it, and reduce costs.

[Brief explanation of the drawing]

Fig. 1 is an overall block diagram of the first embodiment of the present invention, Fig. 2 is a detailed circuit diagram of the main parts of Fig. 1, and Fig. 3 a and b are jacks that also function as switches in the first embodiment. FIG. 4 is an overall block diagram of a conventional low frequency amplifier capable of BTL operation. 1.2... Input terminal, 3... Phase inversion circuit, 4°8.9... Changeover switch, 6...
...Phase inversion and bias switching circuit, 6.7...
・Low frequency amplifier circuit, 10...Speaker, 11・
...Headphones, 16...Plug insulation section, 17.18...Plug input terminal, 19...
... Plug common terminal, 20 ... Jack insulation pad, 21-26 ... Jack terminal, 27.
... Jack base, 100, 102, 103, 1
04゜118.122,123,132,137,13
9゜140.143,146,148,153,154
゜165...Resistance, 105, 106, 107,
108°109.1101111. 112.113,
116°117.119,120,121. 124,
125°126.127.129,130,131.
133°134.135.136.141. 142,
144゜1451149.150.151,162...
...Transistor, 147...Diode,
101°128.153,156,158,162.1
63... Capacitor, 138... Constant current 1fjt. 7.2... Input terminal no... He/F' horn

Claims (1)

[Claims] a first differential amplifier circuit including first and second transistors whose emitters are connected to each other; a second differential amplifier circuit including third and fourth transistors whose emitters are connected to each other; a fifth transistor that supplies current to the emitters of the first and second transistors of the amplifier circuit; and a sixth transistor that supplies current to the emitters of the third and fourth transistors of the second differential amplifier circuit. and the bases of the first transistor and the third transistor are connected so that outputs having opposite phases to each other are obtained from the first and second differential amplifiers, and the bases of the second transistor and the fourth transistor are connected. and at least one of the collectors of the first transistor and the fourth transistor or the collectors of the second and third transistors, and connect these outputs and the input of the fourth class B low frequency amplifier circuit. and connect the first class B low frequency amplifier circuit and the second class B low frequency amplifier circuit to separate loads for input signals applied to the first and fourth transistors or the second and third transistors. When connected, the output signal of the differential amplifier circuit is added so that the output signals of the first and second B class low frequency amplifier circuits are in phase, and the first and second B class low frequency amplifier circuits are connected. A B
When driving a single load with TL connection, the switch is configured so that the output signal of the differential amplifier circuit is applied so that the output signals of the first and second class B amplifier circuits are in opposite phases to each other. The seventh and eighth transistors are configured to operate either the fifth or sixth transistor by switching, and supply current to the bias circuit of the first class B low frequency amplifier circuit by switching the switch. and the second
By operating one of the ninth and tenth transistors, respectively, which supply current to the bias circuit of the B-class low frequency amplifier circuit, and changing the magnitude of the current supplied to the bias circuit, the first and tenth transistors are operated. A low frequency amplifier characterized in that the bias current can be switched at the same time as the load of the low frequency amplifier circuit described in item 2 is switched.