JP5237885B2 - Output circuit - Google Patents

Description

  The present invention relates to an output circuit that converts a voltage into a current, amplifies it, and performs push-pull output. More specifically, the present invention relates to an output circuit that reduces power consumption by reducing the current value of a constant current source in the output circuit when there is no signal in a state where no signal is input to the signal input terminal.

A circuit as shown in FIG. 6 is known as a conventional output circuit that converts a conventional input signal into a current, amplifies it, and outputs the entire range from the ground potential to the power supply voltage, that is, a full swing (for example, Patent Document 1). That is, in FIG. 6, the signal input to the signal input terminal 1 is converted into a current by a conductance amplifier (gm Amp) 2, via the first constant current source 11 between the power supply terminal Vcc and the ground GND. An input stage circuit A that outputs an amplified signal from the emitter thereof, which is amplified by the connected pnp-type first transistor Q1, and a signal output from the input stage circuit A are input, and a pnp-type second transistor An output stage circuit B in which the collectors of the transistor Q2 and the npn-type third transistor Q3 are connected to each other and push-pull connected in series between the power supply terminal Vcc and the ground, and the second and third transistors Q2, And an operating point setting circuit C for setting the operating point of Q3. As shown in FIG. 6, the conductance amplifier 2 is driven by a _sixth constant current source 16 (current value I ₆ ) so that a constant current I ₁ flows through the first constant current source 11. It is configured. Further, the idling currents I ₉ and I ₁₀ are set to flow through the second and third transistors Q2 and Q3 of the output stage circuit B, respectively.

The operating point setting circuit C has a constant current between the first connection point 4 connecting the collector of the npn-type fourth transistor Q4 and the emitter of the pnp-type fifth transistor Q5 and the power supply terminal Vcc. A _second constant current source 12 for passing I ₂ is connected, and a constant current I is connected between the second connection point 5 connecting the emitter of the fourth transistor Q4 and the collector of the fifth transistor Q5 and the ground GND. _{A third} constant current source 13 for passing 3 is connected. The base of the fourth transistor Q4, two of the seventh constant current source 17 and the base and collector of flowing a constant current I ₇ connected in series between the power supply terminal Vcc and the ground GND are short-circuited The base of the fifth transistor Q5 is connected to the connection point of the npn-type eighth and ninth transistors Q8 and Q9, and two bases connected in series between the power supply terminal Vcc and the ground GND a collector connected to a connection point between the constant current source 18 of the eighth flow and transistors Q10, Q11 of the first 10 and second 11 of the pnp shorted constant current I _8, second and third output stage circuit B The operating point of the transistor is set (idling current is set).

At this time, when a small terminal resistance of, for example, about 75Ω is connected to the signal output terminal 3 as a load, the signal current flowing through the load is large, so that the base currents of the second and third transistors Q2 and Q3 also increase. . Therefore, it is necessary to sufficiently increase the current for driving the bases of the second and third transistors Q2 and Q3, and the currents I ₁ , I ₂ and I _{3 of} the constant current sources 11, 12, and 13 are also sufficiently increased. There is a need.

JP2009-33537A

  In the configuration of the output circuit as described above, the circuit current increases. On the other hand, for example, when this type of output circuit is used for video output of a digital camera, or when the rise of the IC is early but the rise of the system is delayed, it is related to other circuit configurations of the set. In some cases, no input signal is input to the output circuit even though the power switch is on. In such a case, a current flows through the output circuit itself, but it does not function as an output circuit because there is no input signal. In particular, in the circuit as shown in FIG. 6, the constant current source is directly inserted between the power supply terminal Vcc and the ground GND via a transistor or the like, so that a large current flows immediately when the power switch is turned on. Will be. Therefore, the output circuit itself is in an operating state due to the relationship with the set, etc., but if there is a lot of time when there is no signal input, useless large current flows through the constant current sources 11 to 13 and 16 to 18 described above, There is a problem that wasteful power consumption is large.

  The present invention has been made to solve such a problem. When no input signal is input to the signal input terminal in the output circuit, at least the driving current of the constant current source is reduced and the signal is input. An object of the present invention is to provide an output circuit that can be set to a regular constant current so that it can be driven with a large current.

An output circuit according to the present invention inputs an input signal to a conductance amplifier to convert it into a current, and inputs the input signal to a base of a first transistor connected via a first constant current source between a power supply terminal and ground. An input stage circuit that outputs an amplified signal from the emitter or collector of the first transistor, a pnp- type second transistor, and an npn-type third transistor are connected in series between the power supply terminal and the ground. The output stage circuit for push-pull amplification and the collector and emitter of the npn-type fourth transistor are connected to the emitter and collector of the pnp-type fifth transistor, respectively, and the first connection point and the second connection, respectively. And connecting the first connection point to a power supply terminal via the second constant current source or the first constant current source and the first transistor The second connection point is connected to the ground via a third constant current source and to the base of the third transistor, and the second transistor is connected to the base of the third transistor. 4 and the operating point setting circuit for setting the operating point of the second and third transistors by the respective base of the fifth transistor applying a predetermined voltage to detect the presence or absence of entering-power signal, said input signal A constant current source control circuit for reducing the current value of the first to third constant current sources when there is no signal , and the low current control circuit has a signal voltage appearing at the base of the third transistor. And a voltage at a connection point of the sixth transistor and the fourth constant current source of the npn-type sixth transistor and the fourth constant current source connected in series between the power supply terminal and the ground, or Previous The fifth constant current source of the fifth constant current source and the pnp-type seventh transistor connected in series between the signal voltage appearing at the base of the second transistor and the power supply terminal and the ground. 7 comparing the voltage at the connection point of the transistor 7, comparing the peak detection circuit for detecting the amplitude of the AC component from the output signal of the amplifier, and whether or not the output of the peak detection circuit is greater than a predetermined voltage And a control signal generating circuit for sending a control signal for changing the current value of the constant current source to each of the constant current sources according to the output of the comparator .

The output circuit according to the present invention inputs an input signal to a conductance amplifier, converts the input signal into a current, and supplies the current to a base of a first transistor connected via a first constant current source between a power supply terminal and the ground. An input stage circuit that inputs and outputs an amplified signal from the emitter or collector of the first transistor, and a pnp-type and npn-type second and third transistors are connected in series between the power supply terminal and the ground. The output stage circuit for push-pull amplification and the collector and emitter of the npn-type fourth transistor are connected to the emitter and collector of the pnp-type fifth transistor, respectively, and the first connection point and the second connection, respectively. The first connection point is connected to a power supply terminal via the second constant current source or the first constant current source, and the first transistor The output terminal and the base of the second transistor are connected, the second connection point is connected to the ground via a third constant current source, and is connected to the base of the third transistor, and the fourth and An operating point setting circuit for setting operating points of the second and third transistors by applying a predetermined voltage to the base of the fifth transistor, and the presence or absence of the input signal, and the absence of the input signal And a constant current source control circuit for reducing the current value of the first to third constant current sources, and the constant current source control circuit is connected to the output terminal of the input stage circuit. A filter circuit that inputs a signal from any of the positions, cuts the DC component, an amplifier that amplifies the output of the filter circuit, and peak detection that detects the amplitude of the AC component from the output signal of the amplifier And a comparator for comparing whether or not the output of the peak detection circuit is greater than a predetermined voltage, and a control signal for changing the current value of the constant current source according to the output of the comparator to each of the constant current sources it is also possible to adopt a configuration that has been closed and a signal generating circuit.

  A multi-channel output circuit in which a plurality of output circuits for outputting the amplified signal having the same input signal are provided in parallel, wherein the constant current source control circuit is provided in one output circuit, and the constant current By using the source control circuit to control the constant current source of another output circuit that is not provided with the constant current source control circuit, the power consumption can be reduced while reducing the circuit configuration. .

  According to the present invention, even if the output circuit is turned on in relation to other circuits in the set, it is detected whether or not a signal is input to the signal input terminal, and no signal is input. In this case, the current value generated by the constant current source is reduced, and when the signal is input to the signal input terminal, the current value generated by the constant current source is immediately restored to the desired current value. Even when the impedance of the load connected to the signal output terminal is small and a large current is required, it can be driven with a large current and can be operated without abnormality. Moreover, the current drop when there is no signal can be lowered to the extent that the feedback circuit of the circuit cannot be cut off (used in the actual circuit with feedback), so about 80 to 90% of the desired current value is reduced. Can be reduced. For this reason, for example, when the power switch is turned on due to a set, such as a video operation of a digital camera, the video operation is not performed and a time when no signal is input continues for a long time. Power consumption can be greatly reduced, which is very effective. In this case, not only the first to third constant current sources described above but also the fourth to eighth constant current sources are used as shown in FIGS. 1 and 2, these constant current sources are used. The current value of the current source can also be reduced, and the power consumption can be further reduced. The present invention is particularly effective when the output current is large.

  In addition, for example, when the same signal is separately processed by R, G, B, etc., such as in a color image, when different output circuits are formed for each, Y, Pb, Pr ( In the case of having three channels with respect to luminance and color difference, the input signal is the same and the output circuit has the same configuration. Therefore, the constant current source control circuit is provided in only one output circuit, and the other output circuit is provided. The current value of the constant current source can be controlled by the constant current source control circuit provided in the one output circuit, and a large current reduction effect can be obtained without increasing the occupied area of the IC chip so much. it can.

It is a circuit explanatory drawing which shows one Embodiment of the output circuit which has a constant current source control circuit part of this invention. It is a circuit explanatory drawing which shows other embodiment of the output circuit which has a constant current source control circuit part of this invention. It is explanatory drawing which shows the other structural example of the constant current source control circuit part of FIG. FIG. 2 is an explanatory diagram showing a conceptual diagram sharing a constant current source control circuit when the output circuit of FIG. 1 is provided in multiple channels with the same input signal. FIG. 5 is an explanatory diagram of an example in which the configuration of FIG. 4 is illustrated using the circuit example of FIG. 1. It is a circuit diagram which shows an example of the output circuit of what is called a full swing which can convert the conventional input signal into an electric current, and can output it in the whole range of a power supply voltage.

  Next, the output circuit of the present invention will be described with reference to the drawings. The output circuit according to the present invention converts an input signal into a current by a conductance amplifier (gm Amp) 2 as shown in a circuit diagram of one embodiment in FIG. 1, and is connected between a power supply terminal Vcc and a ground GND. An input stage circuit A that outputs an amplified signal from the emitter or collector of the first transistor Q1 connected through the first constant current source 11, and pnp-type and npn-type second and third transistors Q2, Q3 Is connected in series between the power supply terminal Vcc and the ground GND, and the operating point setting for setting the operating point of the output stage circuit B that performs push-pull amplification and the second and third transistors Q2 and Q3 of the output stage circuit B. Circuit C and a constant current source system that detects the presence or absence of an input signal and reduces (changes) the current values of at least the first to third constant current sources 11, 12, and 13 when there is no input signal. It is provided and the circuit D.

In the example shown in FIG. 1, the input stage circuit A inputs the signal input to the signal input terminal 1 to the input terminal of the conductance amplifier (gm Amp) 2 driven by the sixth constant current source 16. The voltage of the signal is converted into a current, and is input to the base of a first transistor Q1 of, for example, a pnp type connected via the first constant current source 11 between the power supply terminal Vcc and the ground GND. The first transistor Q1 is amplified by the amplification factor h _fe times and taken out from the emitter. The conductance amplifier 2 can be configured by, for example, a differential pair of two npn transistors, and a constant current source having an npn collector connected to the lower side of the emitter can be a sixth constant current source 16. Although the conductance amplifier 2 can be operated by connecting a pair of resistors without using the sixth constant current source 16, the output of the conductance amplifier 2 is as shown in the example shown in FIG. In addition, when the AC current is taken out, the voltage gain (Gv) of the conductance amplifier 2 can be considered easily, so it is preferable to use a constant current source. In the example shown in FIG. 1, a pnp transistor is used as the first transistor Q1, but an npn transistor may be used. In this case, other types of transistors are also used in reverse type (pnp type and npn type).

  As the constant current source such as the first constant current source 11, a general constant current source formed by applying a constant voltage to the base of the transistor can be used. It has at least two different types of constant current sources, and the current value can be switched depending on the presence or absence of an input signal, as will be described later, by a changeover switch that is switched by a signal such as “low” or “high”. In the figure, it is indicated by a variable symbol. For example, when two types of constant current sources are used for switching, the first type constant current source having a large current value supplies a current that can be supplied to a load connected to the signal output terminal 3. The second type constant current source that is set to a value that can be driven and reduces the current value only needs to maintain the circuit to such an extent that the feedback loop used in the circuit configuration is not broken. About 80 to 90% of the constant current source can be reduced (to a current value of about 10 to 20% during actual operation).

  The first constant current source 11 is configured not only to drive the first transistor Q1 but also to drive the base of the second transistor Q2. In the example shown in FIG. The constant current source 12 is connected between the power supply terminal Vcc, the first connection point 4 which is the connection point between the collector of the fourth transistor Q4 and the emitter of the fifth transistor Q5, and the first connection Since the point 4 is also connected to the emitter of the first transistor Q1 and the base of the second transistor Q2, the first and second constant current sources 11 and 12 are jointly connected to the first transistor Q1 and the second transistor Q2. The base of the transistor Q2 and the fourth and fifth transistors Q4 and Q5 are driven. Therefore, in such a circuit example, by adjusting the current value of the first constant current source 11, the second constant current source 12 can be omitted and only the first constant current source 11 can be used. You can also.

  In the example shown in FIG. 1, the output stage circuit B is configured such that a pnp-type second transistor Q2 and an npn-type third transistor Q3 connect their collectors to each other between the power supply terminal Vcc and the ground GND. Are connected in series, and are configured as a push-pull amplifier circuit having the collector connection point as the signal output terminal 3. The second and third transistors Q2 and Q3 can also be connected by an emitter with the transistor type reversed, and the connection point of the emitter can be the signal output terminal 3. However, if the emitter is used as an output terminal, a voltage drop occurs between the base and emitter of the transistor, and an output corresponding to the voltage drop cannot be made, so that a full swing output cannot be obtained. Therefore, in order to obtain a full swing output, as shown in FIG. 1, it is preferable that the connection point is an output terminal 3 as a collector connection.

The operating point setting circuit C sets the base potentials of the second and third transistors Q2 and Q3 to set the idling current to a desired current value. That is, the emitter current of the first transistor Q1 changes according to the input AC signal, and the base current of the second transistor Q2, the current I ₁₁ flowing through the fourth transistor Q4, and the fifth transistor Q5 according to this change. current I ₁₂ is changed to flow in, as a result, it has a configuration that also changes the base current of the third transistor Q3. Specifically, the collector of the npn-type fourth transistor Q4 is connected to the emitter of the pnp-type fifth transistor Q5 to be the first connection point 4, and the first connection point 4 is Are connected to the emitter of the transistor Q1 and the base of the second transistor Q2, and to the power supply terminal Vcc via the second constant current source 12 (current value I ₂ ). Further, the emitter of the fourth transistor Q4 and the collector of the fifth transistor Q5 are connected to form a second connection point 5, which is connected to the third constant current source 13 (current value I ₃ ) To the ground GND and to the base of the third transistor Q3 of the output stage circuit B.

Further, since a predetermined voltage is applied to the bases of the fourth and fifth transistors, the seventh constant current source 17 (current value I ₇ ), the base and the collector are short-circuited between the power supply terminal Vcc and the ground GND. The two npn-type eighth and ninth transistors Q8 and Q9 are connected in series, and the connection point between the seventh constant current source 17 and the eighth transistor Q8 is the base of the fourth transistor Q4. Connected with. In addition, two pnp-type tenth and eleventh transistors Q10 and Q11 whose base and collector are short-circuited between the power supply terminal Vcc and the ground GND, and an eighth constant current source 18 (current value I ₈ ) Are connected in series, and the connection point between the eleventh transistor Q11 and the eighth constant current source 18 is connected to the base of the fifth transistor Q5, whereby the second and third transistors Q2, Q3 are connected. An operating point, that is, an idling current is set.

  The eighth and ninth transistors Q8 and Q9 have a diode structure by short-circuiting the base and collector of the npn-type transistor. As will be described later, the base-emitter voltage of the third transistor Q3 is Since the setting is related to the base-emitter voltage of the fourth transistor Q4, the pair characteristics of the base-emitter voltage of these transistors and the variation in mass production are suppressed. Since the variation is the same), the transistors are of the same type. However, the base-emitter voltage of the third transistor Q3 is not limited to this configuration as long as a constant and predetermined voltage can be provided regardless of variations in manufacturing. Similarly, the tenth and eleventh transistors Q10 and Q11 are pnp type transistors and their bases and collectors are short-circuited to form a diode structure. Similarly, the bases and emitters of the second transistor Q2 and the fifth transistor Q5 This is to suppress pairing with the inter-voltage and variation during mass production. Further, in the example shown in FIG. 1, these transistors are driven by the seventh or eighth constant current sources 17, 18. However, as shown in the aforementioned Patent Document 1, A configuration in which a constant current source is not used can also be used. However, from the viewpoint of reducing current consumption when there is no signal of the present invention, it is preferable to use a constant current source to lower the current value when there is no signal. That is, the configuration described in Patent Document 1 and the configuration in which the constant current source of the present invention is used to reduce the current value when there is no signal can be properly used depending on the application.

The reason why the DC idling currents I ₉ and I ₁₀ flowing through the second and third transistors Q2 and Q3 can be determined by using this configuration will be described. That, Q8Vbe seventh constant current source 17 by the constant current I ₇ eighth and ninth transistors due to the flow Q8, Q9 of each of the base-emitter voltages, respectively, and Q9Vbe. Further, when the constant current I ₈ flows from the eighth constant current source 18, the base-emitter voltages of the tenth and eleventh transistors Q10 and Q11 are set to Q10Vbe and Q11Vbe, respectively. Then, the fourth transistor Q4 fourth due to current I ₁₁ flows through the Q4Vbe the base-emitter voltage of the transistor Q4, the base of the fifth transistor Q5 due to the current I ₁₂ flows through the fifth transistor Q5 When the emitter-to-emitter voltage is Q5Vbe, the base-emitter voltages Q2Vbe and Q3Vbe of the second and third transistors Q2 and Q3 are respectively Q2Vbe = Q10Vbe + Q11Vbe-Q5Vbe
Q3Vbe = Q8Vbe + Q9Vbe-Q4Vbe
It becomes. From this, it is understood that in order to determine Q2Vbe, it is only necessary to determine each Vbe of the transistors Q10, Q11, and Q5. That the current I ₁₂ and the current I _8, the Vbe of the transistors Q10, Q11, Q5 is determined. At this time, the currents I ₂ and I ₃ are set to be equal, and the currents I ₁₁ and I ₁₂ are set to be equal. At this time, the currents I ₂ , I ₃ , and I ₈ are generated by the constant current sources 12, 13, and 18, respectively. Similarly, the current I ₁₁ and the current I _7, the Vbe of transistors Q8, Q9, Q4 is determined. At this time, the current I ₇ is also generated by the constant current source 17.

In the example shown in FIG. 1, the constant current source control circuit D includes an npn-type sixth transistor Q6 and a fourth constant current source 14 (current value) connected in series between the power supply terminal Vcc and the ground GND. I ₄ ) and the voltage at the emitter of the fourth transistor Q 4 are input to the amplifier 21, canceling the DC component, amplifying the AC component, and passing through the HPF (High Pass Filter) circuit 22. Thus, the direct current component is removed. If the DC component of the amplified signal is sufficiently cut, the HPF circuit 22 need not be provided. The reason for cutting the DC component is to secure the dynamic range of the output of the amplifier 21 and the dynamic range of the input of the peak detection circuit 23 in order to amplify from a small signal to a certain large signal. Then, the amplitude of the AC component is detected by the peak detection circuit 23, and the voltage corresponding to the detected peak size is compared with the reference voltage 24 by the comparator 25 to detect the presence or absence of the input signal. . That is, if the output of the peak detection circuit 23 is larger than the reference voltage 24, it corresponds to the case where there is an input signal. If it is smaller than the reference voltage 24, it can be determined that there is no input signal. Therefore, when there is no input signal, a “high” or “low” signal is sent from the control signal generation circuit 26 to each constant current source, the constant current source is switched, its current value is lowered, and the input signal In some cases, the current value of each constant current source can be controlled to be large.

Specifically, with this configuration, the sixth transistor Q6 is set by setting the current I ₄ and the current I ₁₁ to be equal when there is no signal input to the signal input terminal 1. The base-emitter voltage Q6Vbe of the fourth transistor Q4 is equal to the base-emitter voltage Q4Vbe. Therefore, when there is no signal, the emitter voltage of the sixth transistor Q6 and the emitter voltage of the fourth transistor Q4 are equal to each other, and both are canceled by inputting them into the amplifier 21, and the AC passing through the HPF circuit 22 is canceled. Since there is no signal, the output of the peak detection circuit 23 is also lost, and the comparator 25 becomes lower than the reference voltage 24, and it can be seen that no signal is input to the signal input terminal 1.

  On the other hand, when a signal is input to the signal input terminal 1, an AC signal current flows from the collectors of the second and third transistors Q2 and Q3 to the load connected to the signal output terminal 3. Therefore, an AC signal is generated at the base of the third transistor Q3 in accordance with the change in the collector current of the third transistor Q3. Since this AC signal is superimposed on the DC voltage of the emitter of the fourth transistor Q4 and input to the amplifier 21, the DC component is substantially canceled with the emitter voltage of the sixth transistor Q6, and the AC component has a desired signal amplitude. Is amplified. Then, the DC component is cut by the HPF circuit 22 and input to the peak detection circuit 23 as a desired signal. After the peak value of the AC signal is detected, it is output from the peak detection circuit 23 as a desired DC voltage. Then, when the signal input to the comparator 25 together with the predetermined voltage 24 and compared and detected is larger than the predetermined voltage 24, the second and third transistors Q2 and Q3 can be driven in response to a large load current. Thus, in order to supply a sufficient base current, a signal for controlling the current value of each constant current source is sent from the control signal generation circuit 26 to each constant current source.

  In the example shown in FIG. 1, in order to detect the presence or absence of an AC signal generated at the base of the third transistor Q3, in order to cancel the DC voltage of the emitter of the fourth transistor Q4, the power supply terminal Vcc and the ground GND The sixth transistor Q6 and the fourth constant current source 14 are inserted between them to extract the emitter voltage of the sixth transistor Q6. For example, an AC signal generated at the base of the second transistor Q2 is detected. In this case, for example, as shown in a circuit diagram similar to FIG. 1 in FIG. 2, the fifth constant current source 15 and the pnp-type first power source 15 are connected between the power supply terminal Vcc and the ground GND. 7 transistors Q7 are connected in series, and the emitter voltage of the seventh transistor Q7 and the signal appearing at the base of the second transistor Q2 are input to the amplifier 21. As in the case described above, it can be detected whether or not a signal to be amplified is input to the signal input terminal 1. And like the above-mentioned example, the useless current can be controlled by controlling the current value of each constant current source. In FIG. 2, the same parts as those in FIG.

In each of the above-described examples, the DC component of the base signal of the second or third transistor Q2, Q3 is canceled from the signal generated at the base of the second or third transistor Q2, Q3 and the other DC signal. Although the AC signal is extracted, it is also possible to directly extract the AC signal without using another DC signal. For example, the same effect can be obtained by taking out the AC signal by directly cutting the DC component of the base signal of the second or third transistor Q2, Q3 by the HPF circuit. However, in that case, the HPF circuit must be a circuit that has a sufficiently large input impedance and does not affect the original AC currents of the currents I ₁₁ and I ₁₂ . An example of this is shown in FIG. That is, in FIG. 3, the signal of the emitter voltage of the fourth transistor Q4 shown in FIG. 1 (the same as the base voltage of the third transistor Q3) is directly input to the HPF circuit 27 to cut the DC component. Then, the AC component is amplified by the amplifier 21, sent to the peak detection circuit 23, and the presence or absence of signal input to the signal input terminal 1 is detected in the same manner as in the above example, and the current of each constant current source is similarly detected. The value can be controlled. Here, the HPF circuit 27 cuts the DC component, but is not limited to this, and other filter circuits capable of cutting the DC component can be used. Note that if the DC component is completely cut by the HPF circuit 27 and the AC component changes up and down around 0, it is difficult to obtain the peak-to-peak amplitude, so the output of the amplifier 21 and the ground GND It is preferable to provide a bias setting circuit 28 such as connecting a resistor of a constant value between them. In FIG. 3, although details of the circuit are omitted, the circuit is the same as that of FIG. 1 except for the sixth transistor Q6 and the fourth constant current source. In this example, a signal is extracted from the emitter of the fourth transistor Q4 and the AC component is detected. However, the signal is extracted at the output terminal of the input stage circuit A (the emitter of the first transistor Q1). The presence or absence of an input signal can be similarly detected from any position on the connected connection line.

  Further, from the idea shown in FIG. 3, the detection signal for the presence / absence of the input signal is extracted from the connection line connected to the output terminal of the input stage circuit A (limited to the bases of the second or third transistors Q2 and Q3). As long as it is taken out so as not to cause signal loss, it can be taken out directly from the signal input terminal 1.

  FIG. 4 is a diagram applied to the case of multiple channels in which the same input signal is provided and similar output circuits are formed in parallel. That is, for example, in a color display device or the like that performs signal processing for each of R, G, and B, the original signals of R, G, and B are the same, and the output circuit has the same configuration. Become. In such a case, if the constant current source control circuit D is formed in one output circuit 31 without forming the constant current source control circuit D in each output circuit, the signal of the constant current control circuit D is transmitted. Directly sent to the other output circuits 32 and 33, the current value of the constant current source of each output circuit 32 and 33 can also be controlled. Such an example is not limited to the case of R, G, and B. For example, in the case of Y, Pb, and Pr that adjust the luminance and the color difference, the configuration of the input signal and the output circuit is the same. The indicated application can be applied. With this configuration, when the power is turned on but the signal to be amplified is not input, the current value of the constant current source can be set without increasing the occupation area of the IC forming the circuit so much. The effect of reducing the power consumption can be obtained.

  A specific circuit example of the configuration shown in FIG. 4 is shown in FIG. That is, in FIG. 5, the output circuit shown in FIG. 1 is configured with two channels, the constant current source control circuit D is formed in only one output circuit 31, and the constant current formed in the one output circuit 31 is formed. An example in which the current value of each constant current source of the other output circuit 32 is also controlled by the source control circuit D is shown.

  The present invention is incorporated in an IC or the like and can be used for a large current drive push-pull amplifier circuit or a full swing output amplifier circuit using a bipolar transistor, and can be used for various electric devices such as a TV.

1 signal input terminal 2 conductance amplifier (gm Amp)
DESCRIPTION OF SYMBOLS 3 Signal output terminal 4 1st connection point 5 2nd connection point 11-18 Constant current source Q transistor A Input stage circuit B Output stage circuit C Operating point setting circuit D Constant current source control circuit

Claims (4)

An input signal is input to a conductance amplifier, converted into a current, and input to the base of a first transistor connected via a first constant current source between a power supply terminal and ground, and the first transistor An input stage circuit that outputs an amplified signal from the emitter or collector of
an output stage circuit configured to connect a pnp-type second transistor and an npn-type third transistor in series between a power supply terminal and the ground and perform push-pull amplification;
The collector and emitter of the npn-type fourth transistor are connected to the emitter and collector of the pnp-type fifth transistor, respectively, so as to be a first connection point and a second connection point, respectively. The second constant current source or the first constant current source is connected to a power supply terminal and is connected to the output terminal of the first transistor and the base of the second transistor, and the second connection point is The second and third transistors are connected to the ground through a third constant current source and connected to the base of the third transistor, and a predetermined voltage is applied to the bases of the fourth and fifth transistors, respectively. An operating point setting circuit for setting the operating point of the transistor of
A constant current source control circuit that detects the presence or absence of the input signal and reduces the current value of the first to third constant current sources when there is no input signal.
An output circuit having bets, said constant current source control circuit,
The signal voltage appearing at the base of the third transistor, the power supply terminal and the ground in series with a connected npn-type sixth transistor and a fourth constant-current source of said sixth transistor and the fourth between An amplifier for inputting the voltage at the connection point of the constant current source;
A peak detection circuit for detecting the amplitude of the AC component from the output signal of the amplifier;
A comparator that compares whether the output of the peak detection circuit is greater than a predetermined voltage;
The organic to that output circuit and a control signal generating circuit to send to each of the constant-current source a control signal for changing the current value of the constant current source by the output of the comparator. An input signal is input to a conductance amplifier, converted into a current, and input to the base of a first transistor connected via a first constant current source between a power supply terminal and ground, and the first transistor An input stage circuit that outputs an amplified signal from the emitter or collector of
an output stage circuit configured to connect a pnp-type second transistor and an npn-type third transistor in series between a power supply terminal and the ground and perform push-pull amplification;
The collector and emitter of the npn-type fourth transistor are connected to the emitter and collector of the pnp-type fifth transistor, respectively, so as to be a first connection point and a second connection point, respectively. The second constant current source or the first constant current source is connected to a power supply terminal and is connected to the output terminal of the first transistor and the base of the second transistor, and the second connection point is The second and third transistors are connected to the ground through a third constant current source and connected to the base of the third transistor, and a predetermined voltage is applied to the bases of the fourth and fifth transistors, respectively. An operating point setting circuit for setting the operating point of the transistor of
A constant current source control circuit that detects the presence or absence of the input signal and reduces the current value of the first to third constant current sources when there is no input signal.
An output circuit having bets, said constant current source control circuit,
The signal voltage appearing at the base of the second transistor, the fifth constant current source of the fifth seventh transistor of the constant current source and pnp type and the second being connected in series between a power supply terminal and the ground An amplifier for inputting a voltage at a connection point of 7 transistors;
A peak detection circuit for detecting the amplitude of the AC component from the output signal of the amplifier;
A comparator that compares whether the output of the peak detection circuit is greater than a predetermined voltage;
The organic to that output circuit and a control signal generating circuit to send to each of the constant-current source a control signal for changing the current value of the constant current source by the output of the comparator. An input signal is input to a conductance amplifier, converted into a current, and input to the base of a first transistor connected via a first constant current source between a power supply terminal and ground, and the first transistor An input stage circuit that outputs an amplified signal from the emitter or collector of
an output stage circuit that push-pull-amplifies the pnp-type and npn-type second and third transistors connected in series between the power supply terminal and the ground;
The collector and emitter of the npn-type fourth transistor are connected to the emitter and collector of the pnp-type fifth transistor, respectively, so as to be a first connection point and a second connection point, respectively. The second constant current source or the first constant current source is connected to a power supply terminal and is connected to the output terminal of the first transistor and the base of the second transistor, and the second connection point is The second and third transistors are connected to the ground through a third constant current source and connected to the base of the third transistor, and a predetermined voltage is applied to the bases of the fourth and fifth transistors, respectively. An operating point setting circuit for setting the operating point of the transistor of
A constant current source control circuit that detects the presence or absence of the input signal and reduces the current value of the first to third constant current sources when there is no input signal.
An output circuit having the constant current source control circuit,
A filter circuit that inputs a signal from any position of a connection line to which an output terminal of the input stage circuit is connected, and cuts a DC component;
An amplifier for amplifying the output of the filter circuit;
A peak detection circuit for detecting the amplitude of the AC component from the output signal of the amplifier;
A comparator that compares whether the output of the peak detection circuit is greater than a predetermined voltage;
A control signal generating circuit for sending a control signal for changing the current value of the constant current source to each of the constant current sources by the output of the comparator
Output circuit that have a door. A multi-channel output circuit in which a plurality of output circuits for outputting the amplified signal having the same input signal are provided in parallel, wherein the constant current source control circuit is provided in one output circuit, and the constant current the source control circuit, the output circuit according to any one of claims 1 to 3 for controlling the constant current source of another output circuit constant current source control circuit is not provided.

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