JPH10190376A - Amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amplifier circuit capable of being operated at a low voltage and with a low current and easily widening the dynamic range of the input and output of a circuit. SOLUTION: An input part 60 and an output part 80 are so-called diode circuit. In this amplifier circuit 50, the change of a signal source VIN appears at the base of transistors Q2 and Q3 through the base and emitter of the transistors Q10 and Q11 and an output current Iout is changed corresponding to it. The large part of the current from current sources I12 and I13 is made to flow into the current source I11 and a current amount flowing to a resistor R1 is little.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit for amplifying a video signal or the like.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a configuration of a video signal amplifier circuit generally used in the prior art. In the amplifier circuit shown in FIG. 3, for example, a signal from the signal source V _IN voltage v
_{When in} is not input, the bases of the transistors Q ₁ and Q ₆ are biased to the voltage v ₀ by the voltage sources V ₁ and V ₂ . When the diode-connected transistors Q ₂ and Q ₅ are formed to have similar characteristics, the same current i ₁ is generated in the resistance elements R ₁ and R ₂ .

[0003] When the signal voltage v _in is input by a signal source V _IN to the base of the transistor Q _1, flows change current .DELTA.i ₁ corresponding to the signal voltage v _in the transistor Q ₂ to which the diode-connected from the resistance element R ₁ . As shown in FIG. 3, the same change current Δi _{1 is} applied to the resistance element R ₂ and the diode-connected transistor Q ₅ in the opposite direction.
Flows. The transistors Q ₂ and Q ₅ in which these changes current is diode connected and converted into a differential voltage,
Input to the bases of transistors Q ₃ and Q ₄ .

The [0004] transistors Q _3, Q ₄ in configured differential amplifier circuit, the transistors Q _3, a differential voltage input to the base of Q ₄ is amplified and outputted to the output terminal T _OUT.

The mutual conductance g _m of the above-described amplifier circuit is given by the following equation.

G _m = i ₂ / (r _E · i ₁ ) (1)

[0006]

However, the conventional amplifier circuit described above has a problem that the input dynamic range cannot be widened. In the circuit shown in FIG. 3, in order to widen the dynamic range of the input, it is necessary to set the resistance value r _E of the resistance element R ₁ or the current value i ₁ of the current source I ₁ large. However, by setting these values increases, the voltage drop across the resistor element R ₁ is increased, the circuit that operates at low voltage, it is difficult to widen the dynamic range.

[0007] Also, each associated output dynamic range and the input bias resistance r _E of the resistance element R _1, the current value i ₁ of the current source I _1, without changing the mutual conductance g _m, arbitrarily bias state it is difficult to change, design change for increasing the dynamic range leads to change in the mutual conductance g _m and the bias state of the circuit.
That is, it is difficult for the conventional amplifier circuit to widen the input dynamic range, and as a result, it is almost impossible to increase the output dynamic range.

The present invention has been made in view of such circumstances, and has as its object to operate at low voltage and low current.
And without changing the mutual conductance g _m of the circuit, not only do you bias can be set arbitrarily to provide an amplifier circuit capable of widening the input and output dynamic range of the circuit easily.

[0009]

To achieve the above object, an amplifier circuit according to the present invention comprises: a first transistor having a base connected to an input voltage source and a collector connected to a first voltage source; And an input unit comprising a second transistor having a collector connected to the first current source, and a second current source having the emitter of the first transistor and the emitter of the second transistor connected. A third transistor having a base connected to the base of the second transistor via a first resistance element, a collector connected to the first voltage source, and an emitter connected to a third current source; A fourth transistor having a collector connected to the base of the third transistor and an emitter connected to the fourth current source; and a second transistor connected to the base of the fifth transistor. And anti-element, the emitter and the third
A fifth transistor having a collector connected to the fifth current source and a base connected to the second resistor, a base and a collector connected to the base of the fifth transistor, Amplifying unit comprising a sixth transistor connected to the emitter of the fourth transistor; a seventh transistor having a base connected to the second voltage source and a collector connected to the first voltage source; An eighth transistor having a base and a collector connected to the base of the fifth transistor via the second resistance element and connected to a sixth current source; and an emitter of the seventh transistor, And a seventh current source connected to the emitter of the eighth transistor.

In the amplifier circuit according to the present invention, most of the current from the first current source flows into the second current source through the collector and the emitter of the second transistor, and flows into the first resistance element. Even if the amount of current is reduced, a predetermined voltage can be applied to the bases of the third and fourth transistors according to the input voltage applied to the base of the first transistor.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a circuit diagram showing one embodiment of an amplifier circuit according to the present invention. As shown in FIG. 1, the amplifying circuit of the present embodiment includes voltage sources V ₁ , V ₂ , current sources I ₁ , I ₂ ,..., I ₈ , npn transistors Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q _D1 , _QD2 ,
It comprises Q _D3 , Q _D4 and resistance elements R ₁ , R ₂ . The voltage values of the voltage sources V ₁ and V ₂ are both v ₀
The current value of the current sources I _{1 to} I ₄ is i ₁ , the current value of the current sources I ₅ and I ₆ is i _3, the current value of the current source I ₇ is i ₂ ,
The current value of the current source I ₈ is 2i ₂ , the resistance value of the resistance element R ₁ is r _E , and the resistance value of the resistance element R ₂ is r ₂ . As shown in the figure, the amplifier circuit of the present example is configured by cascade-connecting the input unit 10, the current / voltage conversion unit 20, and the output unit 30.

The input section 10 includes transistors Q ₁ and Q ₂ , current sources I ₁ , I ₂ , I ₃ and I ₄ and a resistance element R ₁ . They are connected to each other emitters of the transistors Q _1, Q ₂ via the resistor element R _1. The signal source V _IN and the voltage source V ₁ is connected in series to the base of the transistor Q _1, the voltage (v _in + v ₀₎ are supplied. Here, v _in denotes the signal voltage. The voltage v ₀ is supplied to the base of the transistor Q _{2 by} the voltage source V ₂ .

The collector of the transistor Q ₁ is a current source I ₁
And a current source I between the emitter and the ground line 2.
₂ is connected. Similarly, the collector of the transistor Q ₂ is connected to the current source I ₃ , and the current source I ₄ is connected between the emitter and the ground line 2.

The current / voltage converter 20 comprises diode-connected transistors Q _D1 , Q _D2 , Q _D3 , Q _D4 and a resistance element R ₂ . As shown in FIG. 1, the connection point between the base and collector of the transistor Q _D1 is connected to the collector of the transistor Q _1, the emitter is connected to a connection point between the base and collector of the transistor Q _D2, further transistors Q ₄ Connected to the base. The connection point between the base and the collector of the transistor _QD2 is the connection node N
It is connected to the D _1.

The connection point between the base and collector of the transistor Q _D3 is connected to the collector of the transistor Q _2, an emitter connected to a connection point between the base and collector of the transistor Q _D4, it is further connected to the base of the transistor Q ₃ ing. The emitter of the transistor Q _D4 are commonly connected to the emitter of the transistor Q _D2 to node ND _1. Node ND ₁ is connected to the ground line 2 via the resistor element R _2. The connection point between the base and collector of the transistor Q _D1 is connected to the current source I _5, the current i ₃ supplied by the current source I _5. Similarly, transistor Q _D3
Connection point between the base and the collector of which is connected to a current source I _6, the current i ₃ supplied by the current source I _6.

The output section 30 includes transistors Q ₃ and Q ₄ and current sources I ₇ and I ₈ . Transistor Q
₃ is connected to the supply line 1 of the power supply voltage V _CC , the base is connected to the connection point between the base and the collector of the transistor Q _D3 , and the collector of the transistor Q ₄ is connected to the current source I ₇
And the base is connected to a connection point between the base and the collector of the transistor _QD1 . The transistors Q ₃ ,
The emitters of Q ₄ are commonly connected, a current source I ₈ is connected between the connection point and the ground line 2, and a current ₂ i ₂ flows toward the ground line 2. The collector of the transistor Q ₄ is connected to the output terminal T _OUT.

Hereinafter, the operation of the amplifier circuit shown in FIG. 1 will be described. The signal voltage V _in is supplied to the base of the transistor Q ₁ by the signal source V _IN , and accordingly, the difference current shown by the following equation is applied to the resistance element R ₁ connected between the emitters of the transistors Q ₁ and Q _2. Δi ₁ occurs.

Δi ₁ = v _in / r _E (2)

Since the currents i ₁ are supplied to the collectors of the transistors Q ₁ and Q _{2 by} the current sources I ₁ and I ₃ , FIG.
As shown in FIG. 7, the difference current Δi ₁ generated in the resistance element R ₁ appears on the connection point side with the base collectors of the transistors Q _D1 and Q _D3 constituting the current / voltage converter 20. Therefore, in the transistor Q _D2, Q _D4, differential current Δi
A voltage drop corresponding to ₁ occurs. This voltage drop is respectively input to the base of the transistor Q _3, Q _4, is amplified by the transistor Q _3, Q _4. Thus, current .DELTA.i ₂ proportional to the difference current .DELTA.i ₁ to the collector of the transistor Q ₄ is generated and outputted from the output terminal T _OUT.

In the circuit example shown in FIG. 1, the transconductance g _{m of the} circuit can be expressed by the following equation.

Equation 3] _{g m = i 2 / (r} E · i 1) ... (3) that is, the mutual conductance g _m of the circuit as well as the transconductance g _m which is denoted in Formula (1) of the circuit shown in FIG. 2 It is.

However, in this embodiment, the current / voltage
Transistor Q constituting converter 20_D2, Q_D4Directly
The current bias is the resistance element R_TwoVoltage drop and
Transistor Q_D2Or Q_D4Base / collector voltage V_beTo
Determined by Resistance element R_TwoCurrent 2i_ThreeFlows
And the DC bias is (2i_Three・ R_Two+ V_be).

Here, since the resistance value r ₂ of the resistance element R ₂ , which is an element for determining the DC bias of the transistors Q _D2 and Q _D4 , is not included in the equation (3) showing the mutual conductance g _m of the amplifier circuit. without affecting the transconductance g _m, a DC bias of the amplifier circuit can be set arbitrarily.

Here, the input and output dynamic ranges of this amplifier circuit will be considered. In this case, the current sources I ₁ , I ₂ , I ₃ , I ₄ , I ₇ and I ₈ of FIG. 1 are constituted by transistors having a predetermined voltage applied to the base and a resistor connected to the emitter. Let us assume that The base potentials of the transistors Q ₃ and Q ₄ constituting the differential amplifier circuit can be arbitrarily set by the resistance value r ₂ of the resistance element R ₂ and the current value 2i ₃ flowing therethrough,
The base potentials of the transistors Q ₁ and Q ₂ constituting the input section 10 of the amplifier circuit are also substantially (G) without considering the next stage.
Since it can be set arbitrarily between ND + _Vbe + V _CES ) and (V _CC -V _CES ), it is possible to widen the input dynamic range of the amplifier circuit. Here, V _CES indicates a voltage drop when the current sources I ₁ and I ₂ constituting the input unit 10 are saturated.

In the output section 30, the output terminal T
Consider the case where a load resistor is connected to _OUT . The base potentials of the transistors Q ₃ and Q ₄ are (GND + 2i ₃
Since it can be set arbitrarily between (r ₂ + V _be ) and (V _CC -V _be -V _CES ), the output dynamic range of the amplifier circuit can be widened. However, since it is necessary to set the base potentials of the transistors Q ₃ and Q ₄ in consideration of not saturating the current source, the base potentials are changed from (GND + V _be + V _CES ) to (V _CC −V _be −V _CES). )
It is necessary to set up between. Here, V _CES
Indicates a voltage drop at the time of saturation of the current source I ₈ constituting the output section 30 and a voltage drop at the time of saturation of the current sources I ₁ and I ₂ constituting the input section 10. Therefore, in this example, (2i ₃ · r
₂ > V _CES ).

Furthermore, when the saturation time of voltage of the transistor Q ₄ which constitutes the output unit 30 and V _Cesat4, the output dynamic range of the circuit shown in FIG. 1 (GND + V _CES + V
_cesat4 ) to (V _CC -V _CES ).

As described above, the transistors Q ₁ and Q ₂
And the DC bias of Q ₃ and Q ₄ can be set without changing the mutual conductance g _m of the amplifier circuit, so that not only the input dynamic range of the amplifier circuit but also the output dynamic range can be widened. In the present embodiment, the input dynamic range can be set arbitrarily between the _{(GND + V be + V CES} ) to (V _CC -V _CES), the output dynamic range from _{(GND + V CES + V cesat4} ) (V CC -V CES) Can be set arbitrarily until

[0026] As described above, according to this embodiment, the transistor Q ₁ in response to an input signal voltage v _in, Q ₂
Difference current to the resistance element R ₁ which is connected between the emitters of Δ
The i ₁ generated, which was input to the connection point between the base and collector of the transistor Q _D1, Q _D3 constituting the current / voltage converter 20 generates a voltage signal corresponding to the input signal voltage v _in , Transistors Q ₃ , Q
And input to the _fourth base, since amplification and outputs at output 30, can operate at low voltage, and without affecting the transconductance g _m of the circuit, can be arbitrarily set the DC bias input of the circuit And the output dynamic range can be expanded.

However, in this embodiment, if the input dynamic range is to be further expanded, the current source I ₁
May saturate and oscillate. When the output currents of the current sources I ₂ and I ₄ and the resistance value r _E of the resistor R1 are increased in order to widen the dynamic range, the output currents of the current sources I ₁ and I _{3 become} larger than those of the current sources I ₂ and I ₄ . There is a problem that the current becomes larger than the output current and the current increases as a whole. For example, the output current of the current source I ₃ is approximately difference current Δ
minute only i ₁ becomes greater than the output current of the current source I _4.

Second Embodiment FIG. 2 is a circuit diagram showing one embodiment of an amplifier circuit according to the present invention. As shown in FIG. 2, the amplifier circuit 50 of the present embodiment
Is composed of a diode Burton 60, an amplifier 70 and a diode Burton 80. Diode Burton 6
0 is a signal source V _IN , a voltage source V ₁₀ , transistors Q ₁₀ , Q
₁₁ , current sources I ₁₁ , I ₁₂ and I ₁₃ . In the diode Barton 60, between the base and the ground line 2 of the transistor Q _10, the voltage source of the signal source V _IN and the voltage v ₁₀ V
₁₀ are connected in series. Transistor Q ₁₀ has its collector connected to the power supply voltage line 1 and the emitter current source I ₁₁
And to the ground line 2. Transistor Q ₁₁
Has a collector connected to the base and connected to the power supply voltage line 1 via current sources I ₁₂ and I ₁₃ connected in parallel, and an emitter connected to the ground line 2 via the current source I _11. ing. The power supply voltage line 1 has a power supply voltage V of 5 V, for example.
Supply _cc . Here, for example, the output current i ₁₂ of the current source I ₁₂ is the inflow amount to the collector and emitter of the transistor Q _11, the output current i ₁₃ of the current source I ₁₃ is the inflow amount into the resistor R1.

The amplifying unit 70 includes transistors Q ₂ , Q ₃ ,
Q ₄ , Q ₅ , current sources I ₁ , I ₂ , I ₃ and resistance value r _E
Of the resistors R1 and R2. In the amplifier unit 70, the transistor Q ₃ are a collector connected to the power supply voltage line 1, and a base connected to the collector and base of the transistor Q2. The base of the transistor Q _2, Q _3, via the resistor R1, is connected to the base of the transistor Q _11. The emitter of the transistor Q ₂ is, is connected to the emitter of the transistor Q _5, the current source I ₁
Connected to a ground line. Emitters of the transistor Q ₄ of the transistor Q ₃ are connected to ground via a current source I _2. The base of the transistor Q ₄ are,
And it is connected to the collector and the base of the transistor Q _5. The collector of the transistor Q ₄ are, connected to the power supply voltage line 1 via a current source I _3. The base of transistor Q _5, Q ₄ is connected to the base of the transistor Q ₅ through a resistor R2. The output current of the current source I ₃ is i _2, the output current of the current source I ₂ is 2i _2.

The diode barton 80 includes a voltage source V ₁₁ ,
It comprises transistors Q ₁₂ , Q ₁₃ and current sources I ₁₄ , I ₁₅ , I ₁₆ . In the diode Barton 80, between the base and the ground line of the transistor Q _13, the voltage source V ₁₁ of the voltage v ₁₀ are connected in series. Transistor Q
₁₃ has a collector connected to the power supply voltage line 1, and an emitter connected to the ground line via a current source I _14. Transistor Q ₁₂ has its collector connected to the power supply voltage line 1 via a current source I _15, I _16, which are parallel connected with is connected to the base, the ground line emitter via a current source I ₁₄ It is connected.

Here, for example, the output current i of the current source I _16
16 is a flowing amount to the collector and emitter of the transistor Q _12, the output current i ₁₅ of the current source I ₁₅ is the inflow amount into the resistor R2.

In the amplifier circuit 50, when the potential of the signal source V _IN rises, the potential of the emitters of the transistors Q ₁₀ and Q ₁₁ rises accordingly, the current i ₁₂ decreases by Δi, and the current i ₁₃ decreases by Δi. To increase. The current i ₁₅ also increases by Δi. When the potentials at the emitters of the transistors Q ₁₀ and Q ₁₁ rise, the potentials at the bases of the transistors Q ₂ and Q ₃ also rise, and the emitter current of the transistor Q ₃ increases. This reduces the emitter current of the transistor Q ₄ is, the output current I _out is increased by [Delta] I _out that is proportional to .DELTA.i. On the other hand, when the potential of the signal source V _IN decreases, an operation opposite to the above-described case is performed.

In the amplifier circuit 50 shown in FIG. 1, the mutual conductance g _{m of the} circuit is expressed by the following equation (4).

[0034]

Equation 4] _{g m = (i 2 / i} 1) / {2 · (2r e + r E)} ... (4)

[0035] In the above formula (4), r _e represents the emitter resistance of the transistor Q. Here, the DC bias applied to the bases of the transistors Q ₃ and Q ₄ is (V
_CES + V _be ), without affecting the transconductance g _m shown in the above equation (4),
This DC bias can be set arbitrarily. V _CES indicates the voltage drop when the current source I ₁ is saturated, and V _be indicates the transistor Q
₂ shows the voltage drop between the base and emitter of Q _5.

In the amplifier circuit 50, the diode Burton 6
The base potential of the transistor Q _10, Q ₁₁ constituting the 0, be obtained because it can arbitrarily set between the time _{(GND + V CES + V be} ) ~ (V cc -V CES), a wide input dynamic range it can. Here, V _CES indicates a voltage drop when the current sources I ₁₁ , I ₁₂ , I ₁₃ are saturated, and V _be indicates a voltage drop between the base and the emitter of the transistors Q ₁₀ , Q ₁₁ .

In the amplifier circuit 50, the transistor Q
₄ and the potential of the connection node between the current source I ₃ and
Since it can be set arbitrarily between (GND + V _CES + V _cesat4 ) and (V _cc −V _CES ), a wide output dynamic range can be obtained. Here, V _CES is the current source I
₂ and I ₃ indicate the voltage drop at the time of saturation, and V _cesat4 indicates the voltage at the time of saturation of the transistor Q ₄ .

Further, in the amplifier circuit 50, the current sources I ₁₂ ,
Of the output current from the I _13, the most part, to flow into the current sources I _11, even with a reduced current i ₁₃ flowing into the resistor R1, that the transistors Q _2, Q ₃ gives a predetermined potential it can. Therefore, the amplifier circuit 50 can reduce the voltage drop in the resistor R1, and can be applied to a low-voltage circuit. That is, even with a lower supply voltage v ₁₀ of the voltage source V _10, it is possible in the transistor Q _2, Q ₃ gives a predetermined potential. Further, in the amplifier circuit 50, in order to widen the input dynamic range and an output dynamic range, it is not necessary to increase the output current of the current source I _1, it can be reduced the amount of current that is required for the entire circuit.

The present invention is not limited to the embodiment described above. For example, in the amplifier circuit shown in FIGS. 1 and 2, the power supply voltage line 1 may supply a power supply voltage _{Vcc of} 3 V, for example.

[0040]

As described in the foregoing, according to the amplifying circuit of the present invention, without affecting the transconductance g _m of the circuit, it is possible to widen the input and output dynamic range of the circuit, and undervoltage and It can operate with low current.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of an amplifier circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional amplifier circuit.

[Explanation of symbols]

_{V 1, V 2, V 10} , V 11 ... voltage _{source, I 1, I 2, I} 8,
_{I 11, I 12, I 13} , I 14, I 15, I 16 ... current source, Q _{1,
Q 2, Q 3, Q 4} , Q D1, Q D2, Q D3, Q 10, Q 11, Q
₁₂ , Q ₁₃ ... Npn-type transistors, R ₁ , R ₂ , R _I1 ,
R _I2 , R _I3 , R _I4 ... resistance element, P ₁ ... pnp transistor, C ₁ ... capacitor, V _CC ... power supply voltage, GND ... ground potential, 1 ... power supply voltage V _CC supply line, 2 ... ground line

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeshi Yuwaki 5-1 Noguchi Kita, Kokubu City, Kagoshima Prefecture Sony Kokubu Corporation

Claims (4)

[Claims] A first transistor having a base connected to an input voltage source and a collector connected to a first voltage source; a second transistor having a base and a collector connected to a first current source; A second transistor connected to the emitter of the first transistor and the emitter of the second transistor;
An input unit comprising: a current source; a base connected to the base of the second transistor via a first resistance element; a collector connected to the first voltage source; and an emitter connected to the third current source. A connected third transistor, a fourth transistor having a base and a collector connected to the base of the third transistor and an emitter connected to a fourth current source, and a base connected to the fifth transistor; A fifth transistor having an emitter connected to the emitter of the third transistor, a collector connected to the fifth current source, and a base connected to the second resistance element; An amplifier comprising a sixth transistor having a collector connected to the base of the fifth transistor and an emitter connected to the emitter of the fourth transistor; A seventh transistor having a base connected to the second voltage source and a collector connected to the first voltage source; a base and a collector connected to the base of the fifth transistor via the second resistance element; An eighth transistor connected to a sixth current source, and a reference current generator including an emitter of the seventh transistor and a seventh current source connected to the emitter of the eighth transistor; Amplifying circuit having: 2. The amplifier circuit according to claim 1, wherein said fifth current source supplies a half current of said third current source. 3. The amplifier circuit according to claim 1, wherein at least one of said first current source and said sixth current source comprises a plurality of current sources connected in parallel. 4. The amplifier circuit according to claim 1, wherein a resistance value of said first resistance element is equal to a resistance value of said second resistance element.