JP2908149B2 - Operational amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operational amplifier, and more particularly to an operational amplifier having a wide output dynamic range and low current consumption.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional operational amplifier designed so as to widen an output dynamic range. In the figure, reference numeral 51 denotes an inverting input terminal, which is connected to the base of the first PNP transistor 41. A non-inverting input terminal 52 is connected to the base of the second PNP transistor 42. The first and second PNP transistors 41,
The emitters 42 are mutually connected and connected to the power supply 1 via the constant current source 61. First PNP transistor 41
Is connected to the collector of the first NPN transistor 31 and the bases of the second NPN transistors 31 and 32. The collector of the second PNP transistor 42 is connected to the collector of the second NPN transistor 32 and the base of the third NPN transistor 33. The emitter of the first NPN transistor 31 is grounded via the resistor 21, and the emitter of the second NPN transistor 32 is grounded via the resistor 22. The emitter of the third NPN transistor 33 is grounded, and the collector is connected to the power supply 1 via the diodes 72 and 71 and the constant current source 62. Reference numeral 34 denotes a fourth NPN transistor. The collector is connected to the power supply 1, the base is connected to the power supply 1 via the constant current source 62, and the emitter is connected to the output terminal 53. A third PNP transistor 43 has an emitter connected to the output terminal 53, a base connected to the collector of the third NPN transistor 33, and a collector grounded. A constant current source 63 has one terminal connected to the output terminal 53 and the other terminal grounded. From the above, an operational amplifier is configured.

Next, the operation will be described. Now, if the input voltage of the inverting input terminal 51 is increased and the input voltage of the non-inverting input terminal 52 is decreased, the collector current of the first PNP transistor 41 decreases, and the second PNP transistor 42
Collector current increases. As the collector current of the first PNP transistor 41 decreases, the collector current of the first NPN transistor 31 also decreases. First and second NP
Since the N-transistors 31 and 32 form a current mirror circuit, the collector current of the first NPN transistor 31 decreases, so that the collector current of the second NPN transistor 32 also decreases. Due to the increase in the collector current of the second PNP transistor 42 and the decrease in the collector current of the second NPN transistor 32, the third NPN
Current injection into the base of the transistor 33 increases.
For this reason, the collector current of the third NPN transistor 33 increases, and the current sink from the base of the third PNP transistor 43 increases. As a result, the emitter current of the third PNP transistor 43 increases, and the sink current from the output increases.

Conversely, when the input voltage of the inverting input terminal 51 is reduced and the input voltage of the non-inverting input terminal 52 is increased,
Contrary to the above, the emitter current of the fourth NPN transistor 34 increases, and the sweep current to the output increases.

[0005]

FIG. 6 shows input / output characteristics when a conventional operational amplifier is used as a voltage follower. Now, when the constant current source 63 is not provided, as the input voltage is reduced, the minimum output voltage Vmin becomes the sum of the saturation voltage of the third NPN transistor 33 and the base-emitter voltage of the third PNP transistor 43. 6, the output dynamic range was narrowed. For this reason, the constant current source 63 is added to lower the minimum output voltage Vmin even when the input is small, thereby widening the dynamic range as shown by the broken line in the figure.

However, in this circuit, the addition of the constant current source 63 does not always limit the output voltage to the vicinity of the minimum output voltage Vmin. There was a problem that increases.

The present invention has been made to solve the above problems, and has as its object to provide an operational amplifier having a wide dynamic range and no increase in current consumption. .

[0008]

An operational amplifier according to the present invention has an inverting input terminal connected to the base of a first PNP transistor and a non-inverting input terminal connected to the base of a second PNP transistor. Connecting the emitter to a power supply via a constant current source, connecting the collector of the first PNP transistor to the collector and base of the first NPN transistor, and the base of the second NPN transistor; The collector of the second PNP transistor, the collector of the second NPN transistor, and the third NPN transistor.
Connected to the base of the PN transistor, the emitters of the first and second NPN transistors are respectively grounded via resistors, the emitter of the third NPN transistor is grounded, and the collectors are connected to the first and second diodes and the constant. A current source is connected in series to a power supply, a collector of the fourth NPN transistor is connected to the power supply, a base thereof is connected to a connection point between the second diode and the constant current source, and an emitter thereof is connected to an output terminal. The emitter of the third PNP transistor is connected to the output terminal, the base is connected to the collector of the third NPN transistor, the collector is grounded, and the fifth NPN transistor is connected to the third NPN transistor.
The collector of the PN transistor is connected to the output terminal, the base is connected to the collector of the second NPN transistor, and the emitter is grounded via a resistor.

In the operational amplifier according to the present invention, the inverting input terminal is connected to the base of the first NPN transistor, the non-inverting input terminal is connected to the base of the second NPN transistor, and the respective emitters are connected. And grounding via a constant current source, connecting the collector of the first NPN transistor to the collector and base of the first PNP transistor, and the base of the second PNP transistor,
Connecting the collector of the second NPN transistor to the collector of the second PNP transistor and the base of the third PNP transistor, connecting the emitters of the first and second PNP transistors to a power supply via a resistor, 3 PN
Connect the emitter of P transistors to the power supply, the collector first, via the second diode and the constant current source to ground, the collector of the third N PN transistors connected to the power supply, the base third The collector of the PNP transistor, the emitter of which is connected to the output terminal;
The emitter of the NP transistor is connected to the output terminal, the base is connected to the connection point between the second diode and the constant current source, the collector is grounded, and the emitter of the fifth PNP transistor is connected to the power supply via a resistor. And the base is connected to the collector of the second NPN transistor, and the collector is connected to the output terminal.

[0010]

In the operational amplifier according to the present invention, when a voltage that reduces the output voltage is input, the fifth NPN
The transistor operates to increase the sink current from the output and widen the dynamic range. Otherwise, the fifth NPN transistor does not operate, and the current consumption hardly increases.

When a voltage that increases the output voltage is input, the fifth PNP transistor operates,
Increase the sweep current to the output and widen the dynamic range. Otherwise, the fifth PNP transistor does not operate, and the current consumption hardly increases.

[0012]

[Embodiment 1] FIG. 1 is a diagram showing an operational amplifier according to a first embodiment of the present invention. The operational amplifier of the first embodiment is different from the operational amplifier constant current source 63 of FIG.
This is obtained by adding a fifth NPN transistor 35 and a resistor 23. That is, the collector of the fifth NPN transistor 35 is connected to the output terminal 53, and the base thereof is connected to the third NP transistor 35.
Connected to the base of N transistor 33, the emitter of which is grounded via resistor 23.

Next, the operation will be described. When the input voltage of the inverting input terminal 51 is increased and the voltage of the non-inverting input terminal 52 is decreased, the injection of current into the base of the third NPN transistor 33 increases as in the case of the conventional operational amplifier of FIG. Then, the sink current from the output terminal 53 increases. At this time, the current injection into the base of the fifth NPN transistor 35 also increases at the same time, the collector current of the fifth NPN transistor 35 also increases, and the conventional constant current source 63
Works the same as.

Conversely, when the input voltage of the inverting input terminal 51 is reduced and the input voltage of the non-inverting input terminal 52 is increased, the fifth
The current injection into the base of the NPN transistor 35 decreases, and the fifth NPN transistor 35 does not operate.

For example, FIG. 2 shows input / output characteristics when this operational amplifier is used as a voltage follower. When the input voltage is low (when the voltage at the inverting input terminal 51 is high and the voltage at the non-inverting input terminal 52 is low), the fifth NPN transistor 35 operates and the constant current source 6 of the conventional operational amplifier is used.
3, the minimum output voltage Vmin can be reduced to the saturation voltage of the fifth NPN transistor 35, as shown by the solid line in FIG.

On the other hand, when the input voltage is high (when the voltage at the inverting input terminal 51 is low and the voltage at the non-inverting input terminal 52 is high), the fifth NPN transistor 35 does not operate. That is, in the circuit of this embodiment, the current consumption hardly increases except when the input voltage is small. Therefore, by using such a circuit, an operational amplifier having a wide dynamic range and low current consumption can be obtained.

Embodiment 2 FIG. FIG. 3 shows an operational amplifier according to a second embodiment of the present invention. In the figure, reference numeral 51 denotes an inverting input terminal, which is connected to the base of the first NPN transistor 36. 52 is a non-inverting input terminal, and the second NPN
Connected to the base of transistor 37. The emitters of the first and second NPN transistors 36 and 37 are connected,
Grounded via a constant current source 61. The collector of the first NPN transistor 36 is connected to the first PNP transistor 44
And second PNP transistors 44 and 45
Connected to the base. Second NPN transistor 37
Is connected to the collector of the second PNP transistor 45 and the base of the third PNP transistor 46. The emitter of the first PNP transistor 44 is connected to the power supply 1 via the resistor 21, and the emitter of the second PNP transistor 45 is connected to the power supply via the resistor 22. The emitter of the third PNP transistor 46 is connected to the power supply 1 and the collector is grounded via the diodes 71 and 72 and the constant current source 62. Reference numeral 34 denotes a third NPN transistor whose collector is connected to the power supply, whose base is connected to the collector of the third PNP transistor 46, and whose emitter is connected to the output terminal 53. 43 is the fourth
PNP transistor whose emitter is the output terminal 53
And the base is grounded via a constant current source 62,
The collector is grounded.

Reference numeral 47 denotes a fifth PNP transistor,
The emitter is connected to the power supply 1 via the resistor 23, the base is connected to the base of the third NPN transistor 46,
The collector is connected to the output terminal 53. From the above, an operational amplifier is configured.

Next, the operation will be described. Now, when the input voltage of the inverting input terminal 51 is reduced and the input voltage of the non-inverting input terminal 52 is increased, the collector current of the first NPN transistor 36 decreases, and the second NPN transistor 37
Collector current increases. As the collector current of the first NPN transistor 36 decreases, the collector current of the first PNP transistor 44 also decreases. First and second PN
Since the P-transistor 44 and 45 are <br/> Tsu Do a current mirror circuit, a decrease of the collector current of the first PNP transistor 44, also decreases the collector current of the second PNP transistor 45. Due to the increase in the collector current of the second NPN transistor 37 and the decrease in the collector current of the second PNP transistor 45, the third PNP
Current sinking from the base of transistor 46 increases. As a result, the collector current of the third PNP transistor 46 increases, and this current increases the current injection to the base of the third NPN transistor 34, and increases the sweep current to the output. In addition, the current absorption from the base of the fifth PNP transistor 47 has also increased, and the collector current has also increased, thereby further increasing the sweep current to the output. As a result, the output voltage of the output terminal 53 increases.

FIG. 6 shows input / output characteristics when the operational amplifier is used as a voltage follower. Now the fifth PN
Assuming that there is no P transistor 47 and resistor 23,
The maximum output voltage Vmax is calculated from the power supply voltage and the saturation voltage of the third PNP transistor 46 as shown by the broken line in FIG.
, The value obtained by subtracting the base-emitter voltage of the NPN transistor 34, thereby narrowing the dynamic range of the output.

However, in this circuit, as described above, when the input voltage is high (when the voltage at the inverting input terminal 51 is low and the voltage at the non-inverting input terminal 52 is high), the fifth PNP transistor 47 operates. The maximum output voltage Vmax can be increased to a value obtained by subtracting the saturation voltage of the fifth PNP transistor 47 from the power supply voltage as shown by the solid line in FIG.

On the other hand, when the input voltage is low (when the voltage at the inverting input terminal 51 is high and the voltage at the non-inverting input terminal 52 is low), the fifth PNP transistor 47 does not operate. That is, in the circuit of this embodiment, the current consumption hardly increases except when the input voltage is large. Therefore, by using such a circuit, an operational amplifier having a wide dynamic range and low power consumption can be obtained.

[0023]

As described above, according to the operational amplifier of the present invention, a current source consisting of a transistor and a resistor that operates only when the input voltage is small or large is added, so that the dynamic There is an effect that an operational amplifier having a wide range and small current consumption can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an operational amplifier according to an embodiment of the present invention.

FIG. 2 is an input / output characteristic diagram for explaining the operation of the configuration of FIG. 1;

FIG. 3 is a circuit configuration diagram of an operational amplifier according to a second embodiment of the present invention.

FIG. 4 is an input / output characteristic diagram for explaining the operation of the configuration of FIG. 3;

FIG. 5 is a circuit configuration diagram of a conventional operational amplifier.

FIG. 6 is an input / output characteristic diagram for explaining the operation of the configuration of FIG. 5;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Power supply 21, 22, 23 Resistance 31, 32, 33, 34, 35, 36, 37 NPN transistor 41, 42, 43, 44, 45, 46, 47 PNP transistor 51 Inverting input terminal 52 Non-inverting input terminal 53 Output terminal 61, 62, 63 Constant current source 71, 72 Diode

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03F 3/45 H03F 1/02

Claims (2)

(57) [Claims] 1. An inverting input terminal is connected to a base of a first PNP transistor, a non-inverting input terminal is connected to a base of a second PNP transistor, and respective emitters are connected to each other via a constant current source. And the collector of the first PNP transistor is connected to the collector and base of the first NPN transistor and the second NPN transistor.
Connecting the collector of the second PNP transistor to the collector of the second NPN transistor and the base of the third NPN transistor;
The emitters of the first and second NPN transistors are grounded via respective resistors, the emitter of the third NPN transistor is grounded, and its collector is connected in series with the first and second diodes and a constant current source. Connecting to the power supply, connecting the collector of the fourth NPN transistor to the power supply,
The base is connected to the connection point between the second diode and the constant current source, the emitter is connected to the output terminal, the emitter of the third PNP transistor is connected to the output terminal, and the base is connected to the third NPN. The collector of the transistor was connected to ground, the collector of the fifth NPN transistor was connected to the output terminal, the base was connected to the collector of the second NPN transistor, and the emitter was grounded via a resistor. An operational amplifier, characterized in that: 2. An inverting input terminal is connected to a base of a first NPN transistor, a non-inverting input terminal is connected to a base of a second NPN transistor, and respective emitters are connected to each other via a constant current source. The collector of the first NPN transistor is connected to the collector and base of the first PNP transistor and the base of the second PNP transistor, and the collector of the second NPN transistor is connected to the collector of the second PNP transistor. ,
And the third PNP transistor is connected to the base of the first PNP transistor.
And connecting the emitter of the second PNP transistor to a power supply via a resistor, connecting the emitter of the third PNP transistor to a power supply,
The collector is grounded through the first and second diodes and the constant current source in series, the collector of the third NPN transistor is connected to the power supply,
The base is connected to the collector of the third PNP transistor, the emitter is connected to the output terminal, the emitter of the fourth PNP transistor is connected to the output terminal, and the base is connected between the second diode and the constant current source. Connected to a connection point, the collector is grounded, the emitter of the fifth PNP transistor is connected to the power supply via a resistor, the base is connected to the collector of the second NPN transistor, and the collector is connected to the output terminal An operational amplifier characterized in that: