JPH09331218A - Amplifier circuit and filter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amplifier circuit which can operate under a low voltage and has input and output dynamic ranges which can be widened easily. SOLUTION: A difference current Δi1 occurs in a resistance element R1 connected between the emitters of transistors Q1 and Q2 in accordance with an input signal voltage vin and the current Δi1 is inputted to the connecting points between the bases and collectors of transistors QD1 and QD3 constituting a current to voltage converting section 20 and generate the voltage signals corresponding to the input signal voltage Vin . The voltage signals are respectively inputted to the bases of transistors Q3 and Q4 constituting an output section 30 and the section 30 outputs the signals after amplification. Therefore, an amplifier circuit can operate under a low voltage and a DC bias can be set arbitrarily from the resistance value of the resistance element R2 of the section 20 and the current 2i1 flowing to the element R2 without giving any influence to the mutual conductance of the circuit. In addition, the input and output dynamic ranges of the circuit can be widened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit and a filter circuit for amplifying, for example, a video signal.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a structure of a video signal amplifier circuit which is generally used in the past. As shown, the conventional amplifier circuit has voltage sources V ₁ , V ₂ , a current source I ₁ ,
I ₂ , I ₃ , npn-type transistors Q ₁ , Q ₂ , Q ₃ ,
It is composed of Q ₄ , Q ₅ , Q ₆ and resistance elements R ₁ , R ₂ . The voltage values of the voltage sources V ₁ and V ₂ are both v ₀ , and the current value of the current source I ₁ is 2i ₁ and the current source I ₂
Has a current value of 2i ₂ , and the current source I _{3 has} a current value of i ₂ ,
The resistance values of the resistance elements R ₁ and R ₂ are both r _E.

The collector of the transistor Q ₁ has a power supply voltage V
_The signal source V _IN and the voltage source V ₁ are connected in series between the base and the ground line 2 and are connected to the _CC supply line 1. The emitter of the transistor Q ₁ is connected to the base of the transistor Q ₂ via the resistance element R ₁ .

The base and collector of the transistor Q ₂ are commonly connected, that is, the transistor Q ₂ is diode-connected. The collector and the base of the transistor Q ₂ are connected to the base of the transistor Q ₃ , the emitter is commonly connected to the emitter of the transistor Q ₅ , and these connection points are connected to the current source I ₁ .

The collector of the transistor Q ₃ has a power supply voltage V
_It is connected to the _CC supply line 1 and has an emitter connected to the transistor Q ₄
Are commonly connected to the emitters of the above, and these connection points are connected to the current source I ₂ . The collector of the transistor Q ₄ is connected to the current source I ₃ , and these connection points are connected to the output terminal T 3.
Connected to _OUT .

The transistor Q ₅ is diode-connected like the transistor Q ₂ , the collector and the base are commonly connected to the base of the transistor Q ₄ , and the resistance element R
It is connected via ₂ to the emitter of the transistor Q ₆ . The collector of the transistor Q ₆ is connected to the supply line 1 of the power supply voltage V _CC , and the voltage source V ₂ is connected between the base and the ground line _2.
Is connected.

In the above-mentioned amplifier circuit, for example,
Source V_INFrom the signal voltage v_inIs not entered,
Langista Q₁And transistor Q₆The base is voltage
Source V ₁, V₂Voltage v₀Biased. Also,
Diode-connected transistor Q₂, Q_FiveIs similar
When formed so as to have characteristics, the resistance element R₁,
R₂Have the same current i₁Is generated.

Transistor Q₁Signal source V at the base of_INTo
Signal voltage v_inIs input, the signal voltage v_inIn response
Change current Δi₁Is the resistance element R₁To diode connection
Transistor Q₂Flows to Also shown in FIG.
In the opposite direction, the resistance element R₂And Daio
-Connected transistor Q_FiveSame change current Δi ₁
Flows. These changing currents are diode-connected
Langista Q₂And Q_FiveIs converted to a differential voltage by
Transistor Q_Three, Q_FourEntered in the base of.

The [0009] 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 transconductance g _m of the above-mentioned amplifier circuit is given by the following equation.

G _m = i ₂ / (r _E · i ₁ ) (1)

[0011]

However, the conventional amplifier circuit described above has a problem that the input dynamic range cannot be widened. In the circuit shown in FIG. 4, in order to widen the input dynamic range, 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.

Also, the output dynamic range and the input
Bias is resistance element R₁Resistance value r _E, Current source I₁No electricity
Flow value i₁Transconductance g_mChange
It is difficult to change the bias state arbitrarily without
Design changes to widen the dynamic range
Conductance g_mIn addition, the bias state is changed.
That is, the conventional amplifier circuit has a wide input dynamic range.
Of the output dynamic level.
It is almost impossible to increase the amount of change.

The present invention has been made in view of such circumstances, and an object thereof is not only to operate at a low voltage but also to set an arbitrary bias without changing the mutual conductance g _{m of the} circuit. An object of the present invention is to provide an amplifier circuit and a filter circuit that can easily widen the input and output dynamic range of the circuit.

[0014]

To achieve the above object, the present invention provides a first transistor having a collector connected to a first current source and a base connected to a first voltage source, and a collector. A second transistor connected to a second current source and a base connected to a second voltage source, and a first resistance element connected between the emitters of the first and second transistors. An input section consisting of
First and second diodes connected in series between the collector of the transistor and the connection node in the forward direction from the collector to the connection node, and the collector of the second transistor. A third diode and a fourth diode connected in series with the connection node in a forward direction from the collector to the connection node, and connected between the connection node and the reference potential. A second resistance element, and a conversion section,
A collector is connected to a power source, a base is connected to a connection point between the first diode and the second diode, and an emitter is connected to a third current source. A third base connected to the current source, a base connected to a connection point between the third diode and the fourth diode, and an emitter connected to the third current source in common with the emitter of the third transistor; 4 transistors and an output section composed of four transistors.

Further, in the present invention, preferably, the fourth current source supplies half the current of the third current source.

Further, according to the present invention, a first transistor having a collector connected to the first current source and a base connected to the first voltage source, and a collector connected to the second current source. A second transistor and a first resistance element connected between the emitters of the first and second transistors, and an input section between the collector and the connection node of the first transistor. Between the first and second diodes connected in series in a forward direction from the collector to the connection node, and between the collector of the second transistor and the connection node, the connection from the collector Third and fourth diodes connected in series in a forward direction toward the node, and a second resistance element connected between the connection node and the reference potential A third transistor having a collector connected to a power source, a base connected to a connection point between the first diode and the second diode, and an emitter connected to a third current source. A collector connected to a fourth current source and a base of the second transistor of the input section, a base connected to a connection point of the third diode and a fourth diode, and an emitter of the third transistor. And an output section including a fourth transistor connected to the third current source in common with the emitter of, and a capacitive element connected between the collector of the fourth transistor and the reference potential.

According to the present invention, the first portion is provided in the input portion of the amplifier circuit.
The signal voltage supplied by the voltage source is input, and, for example, a differential current signal is generated and input to the conversion unit in response to the signal voltage. Current / voltage conversion is performed by the diode that constitutes the conversion unit, and the converted voltage signal is amplified and output by the output unit.

In the converter, the circuit bias is determined by the resistance value of the second resistance element connected between the connection node and the reference potential and the current value flowing through the second resistance element, so that the mutual conductance g _m of the circuit is determined. The bias can be adjusted without affecting the dynamic range of the input and output.

[0019]

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
And the current values of the current sources I _{1 to} I ₆ are i ₁ and the current source I ₇
Has a current value of i ₂ and the current source I _{8 has} a current value of 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 is a transistor Q₁, Q₂, Electric
Source I₁, I₂, I_Three, I_FourAnd the resistance element R₁By
It is configured. Transistor Q₁, Q₂The emitter is
Resistance element R₁Are connected to each other via. Transi
Star Q₁Signal source V connected in series to the base of_INOh
And voltage source V ₁Voltage (v_in+ V₀) Is supplied
You. Where v_inIndicates the signal voltage. Transis
Q₂Voltage source V at the base of₂Voltage v₀Is supplied
You.

The collector of the transistor Q ₁ is the current source I ₁
And a current source I between the emitter and the ground line 2.
₂ is connected. Similarly, the transistor Q ₂ collector 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 is composed of 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 collector of the transistor Q _D2 is connected to the connection node ND ₁ .

The connection point between the base and collector of the transistor Q _D3 is connected to the collector of the transistor Q ₂ , the emitter is connected to the connection point of the base and collector of the transistor Q _D4 , and further 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, current i ₁ is supplied by the current source I _5. Similarly, transistor Q _D3
The connection point between the base and the collector of is connected to the current source I ₆ , and the current source I ₆ supplies the current i ₁ .

The output section 30 is composed of 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.

The operation of the amplifier circuit shown in FIG. 1 will be described below.
explain. Signal source V_INTransistor Q₁Base of
Signal voltage v_inIs supplied and accordingly the Transis
Q₁, Q₂Resistor element connected between both emitters of
R ₁The difference current Δi₁Occurs.

Δi ₁ = v _in / r _E (2)

Transistor Q₁, Q₂Current to the collector of
Source I₁And I_ThreeThe current i₁Is supplied as shown in FIG.
As shown in FIG.₁Difference current Δi₁That
Transistor configuring each current / voltage conversion unit 20
Q_D1, Q_D3Appears at the connection point side with the base collector of. This
Therefore, the transistor Q_D2, Q_D4, The difference current Δi
₁A voltage drop occurs according to. This voltage drop is
Transistor Q_Three, Q _FourThe base of the transition
Star Q_Three, Q_FourAmplified by As a result,
Jista Q_FourDifference current Δi on the collector side of₁Current proportional to
Δi₂Occurs, and the output terminal T_OUTIs output from.

In the circuit example shown in FIG. 1, the mutual conductance 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. 4 Is.

However, in this embodiment, the current / voltage is
Transistor Q constituting converter 20_D2, Q_D4Directly
The current bias is the resistance element R₂Voltage drop and
Register Q_D2Or Q_D4Base / collector voltage V_beTo
Determined by Resistance element R₂Current 2i₁Flows
And the DC bias is (2i₁・ R₂+ V _be).

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

Now consider the input and output dynamic range of this amplifier circuit. 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 forming 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 ₁ flowing through it.
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 ₁
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 ₁ · r
₂ > V _CES ).

When the saturation voltage of the transistor Q ₄ constituting the output section 30 is V _cesat4 , the output dynamic range of the circuit shown in FIG. 1 is (GND + V _CES + V
_It can be set between _cesat4 ) and (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

In this example, an amplifier circuit which can operate at a low voltage, for example, a power supply voltage V _CC of 3V can be constructed. Also,
A plurality of stages of the amplifier circuit shown in FIG. 1 are connected in series, and the output signal of the preceding stage is supplied to the subsequent stage as an input signal, whereby an amplifying circuit with a larger gain can be configured.

As described above, according to this embodiment, the transistors Q ₁ and Q ₂ are supplied _in accordance with the input signal voltage v _in.
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.

Second Embodiment FIG. 2 is a circuit diagram showing an embodiment of the filter circuit according to the present invention. As shown in FIG. 2, the amplifier circuit of this example has voltage sources V ₁ and V _R , current sources I ₁ ′ and I ₂ ′, npn-type transistors Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q _D1 and Q D. _D2 , Q _D3 , Q
_D4 , Q _I1 , Q _I2 , Q _I3 , resistance elements R ₁ , R ₂ , R _I1 , R
_I2 , R _I3 , R _I4 , a pnp type transistor P ₁ , and a capacitor C ₁ . The voltage value of the voltage source V ₁ is v ₀ , and the current values of the current sources I ₁ ′ and I ₂ ′ are 2i.
₁ , 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 FIG. 2, the circuit example of the second embodiment is almost the same as the circuit example of the first embodiment shown in FIG. 1. Hereinafter, with reference to FIG. The difference from the first embodiment will be mainly described. Note that, in FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals.

Similar to the first embodiment, the transistor Q
₁ , Q ₂ , current sources I ₁ ′, I ₂ ′, Q constituting a current source
_{Although the} input section 10a is constituted by _I1 , Q _I2 , the resistance elements R _I1 , R _I2 and the resistance element R ₁ , in the present example, the current source I ₁ 'provides a collector for the transistor Q _{1 and} a collector for the transistor Q _D1 . a current is supplied 2i ₁ to the connection point of the base, by the current source I ₂ ', current 2i ₁ is supplied to the connection point between the collector and the base of the collector and the transistor Q _D2 of the transistor Q _2. Also, FIG.
Similarly, the resistance element R ₁ is connected between the emitters of the transistors Q ₁ and Q _{2 in} the circuit shown in FIG. Transistor Q
₁ of emitter connected to the collector of the transistor Q _I1, the emitter of the transistor Q ₂ is connected to the collector of the transistor Q _I2. The emitter of the transistor Q _I1 is connected to the ground line 2 via the resistance element R _I1, and the emitter of the transistor Q _I2 is connected to the ground line 2 via the resistance element R _I2.
It is connected to the. The bases of the transistors Q _I1 and Q _I2 are connected to the voltage source V _R.

The transistors Q _D1 , Q _D2 , Q _D3 , Q _D4 and the resistance element R ₂ constitute a current / voltage converter 20a. Transistor _{Q D1, Q D2, Q D3} , Q D4 are both diode connected and the emitter of the transistor Q _D2, Q _D4 are commonly connected to the node ND _1, the node ND ₁
Is connected to the ground line 2 via a resistance element R ₂ . Also, the connection point between the base and collector of the transistor Q _D2 is connected to the base of the transistor Q ₄ ,
The connection point between the base and collector of the _D4 is connected to the base of the transistor Q _3.

Transistor Q_Three, Q_Four, Configure the current source
Transistor P₁, Resistance element R_I4, Transistor
Q_I3, Resistance element R_I3The output unit 30a is configured by
You. Transistor Q_Three, Q_FourCommon emitter
Jista Q_I3Of the transistor Q_I3of
The emitter is a resistance element R_I3Connected to the ground wire 2 via
Base is voltage source V_RIt is connected to the. In addition, Tran
Jista Q_FourIs the transistor P₁To the collector
Connected, transistor P₁Is the resistor R_I4
Through the power supply voltage V_CCConnected to the supply line 1 of
Control voltage v_CIs applied. Transistor Q_FourNo
Lector is output terminal T_OUTConnected to the output terminal T
_OUTIs a transistor Q that constitutes the input section 10.₂The
And a feedback loop is formed.

Transistor Q_I1, Q_I2And the resistance element R
_I1, R_I2The current source is constituted by. Transistor
Q₁Signal voltage v at the base of_inIs not entered,
Resistance element R_I1, R_I2Resistance value and voltage source V_RVoltage value
Causes transistor Q_I1, Q_I2Current i₁
Is generated. At this time, the current / voltage conversion unit 20
Transistor Q forming a_D1, Q_D3Current i₁But it
Supplied respectively. Transistor Q₁Signal voltage at the base of
v_inIs input, the transistor Q ₁, Q₂Emi
Resistor R connected between₁Difference current Δi₁But
Is generated.

A current change corresponding to the difference current Δi ₁ is supplied to the current / voltage conversion unit 20a, thereby converted into a voltage and supplied to the bases of the transistors Q ₃ and Q ₄ forming the output unit 30a.

The collector current of the transistor Q _I3 is 2i _{2 depending on} the resistance value of the resistance element R _I3 and the voltage value of the voltage source V _R.
Is set to Further, the voltage value of the control voltage v _C, which is applied to the base of the resistance element R _I4 and transistors P _1, current i ₂ is generated at the collector of transistor P _1, it is supplied to the collector of the transistor Q _4.

The voltage difference supplied to the bases of the transistors Q ₃ and Q ₄ is amplified, and the collector of the transistor Q ₄
That is, the signal voltage v _out is output to the output terminal T _OUT of the amplifier circuit. Further, the output voltage v _out is fed back to the base of the transistor Q ₂ forming the differential amplifier circuit, and, for example, a filter circuit is formed together with the capacitor C ₁ .

The input and output dynamic range of the filter circuit in this embodiment is the same as that of the amplifier circuit shown in FIG. 1, and the resistance element R of the current / voltage converter 20a is used.
By adjusting the resistance value of ₂ and the current values of the current sources I ₁ 'and I ₂ ', the DC bias of the circuit can be set arbitrarily without affecting the mutual conductance g _m of the amplifier circuit, and the input and output can be set. The dynamic range can be expanded. The input and output dynamic range of the filter circuit shown in FIG. 2 will be described below with reference to FIG.

FIG. 3 is a waveform diagram of the filter circuit shown in FIG. FIG. 3A is a waveform diagram of the input signal.
(B) is a waveform diagram of the output signal. As shown in FIG. 3A, when the signal voltage v _in is not input to the filter circuit, the voltage source V ₁ biases the base potential V _IN0 of the transistor Q ₁ to, for example, 1.8V.

In the input section 10a, the transistor Q _1
Has a base / emitter voltage V _be1 , a voltage drop _across the resistance element R _I1 is V _r1 , and a saturation voltage of the transistor Q _I1 is V
_{Assuming cesat1} , the lower limit level V _INL of the input signal is expressed by the following equation.

[0048]

(4) V _INL > V _r1 + V _cesat1 + V _be1 (4) The base / emitter voltage V _{be1 of the} transistor Q ₁ is 0.
7 V, the voltage drop V _r1 generated in the resistance element R _I1 is 0.2 V,
When the saturation voltage V _cesat1 of the transistor Q _I1 is 0.2 V, the lower limit level V _INL of the input signal is 1.1 V according to the equation (4).

Since the upper limit level V _INH of the input signal needs to be considered so as not to saturate the current source I ₁ ′, it is expressed by the following equation.

V _INH <V _CC −V _CESI1 (5) where V _CESI1 is the saturation voltage of the current source I ₁ ′.
When the power supply voltage V _CC is a low voltage of 3 V and the saturation voltage V _CESI1 of the current source I ₁ ′ is 0.4 V, the upper limit level V _INH of the input signal is (V _INH <2. 6
V) should be satisfied.

On the other hand, in the output section 30a, the saturation voltage of the transistor Q ₄ is V _cesat4 , the voltage drop occurring in the resistance element R _I3 is V _r3 , and the saturation voltage of the transistor Q _I3 is V _r .
_{Assuming cesat3} , the lower limit level V _OL of the output signal is expressed by the following equation.

[0051]

(6) V _OL > V _r3 + V _cesat3 + V _cesat4 (6) The saturation voltage of the transistor Q ₄ is 0.2 V for V _cesat4 , 0.2 V for the voltage drop V _r3 generated in the resistance element R _I3 , and the transistor Q _I3. When the saturation voltage V _cesat3 is 0.2 V, the lower limit level V _OL of the output signal is 0.6 V according to the equation (6).

Transistor P₁Saturation voltage is V_cesatP,
Resistance element R_I4The voltage drop across _r4Then the output signal
No. upper limit level V_OHIs expressed by the following equation.

V _OH <V _CC −V _r4 −V _cesatP (7) When the saturation voltage V _cesatP of the transistor P ₁ is 0.2 V and the voltage drop V _r4 generated in the resistance element R _I4 is 0.2 V, From the equation (7), the upper limit level V _OH of the output signal is 2.6V.

In this way, the input and output dynamic range of the filter circuit of FIG. 2 is maintained in a sufficient state.

In the current / voltage conversion unit 20a, the resistance value r ₂ of the resistance element R ₂ can be set so that the bias of both the input unit 10a and the output unit 30a becomes optimum.

Further, the filter circuit shown in FIG. 2 has a plurality of stages, for example, eight stages, connected in series, and the output signal of the preceding stage is inputted to the input terminal of the succeeding stage as the input signal of the succeeding stage, whereby a low voltage, for example, 3V. It is possible to configure a video amplifier circuit that operates with the power supply voltage V _CC of.

[0056]

As described above, according to the amplifier circuit and the filter circuit of the present invention, the input and output dynamic range of the circuit can be widened without affecting the mutual conductance g _m of the circuit, and There is an advantage that it can operate at a low voltage.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing an embodiment of a filter circuit according to the present invention.

FIG. 3 is a waveform diagram of the filter circuit shown in FIG.

FIG. 4 is a circuit diagram showing an example of a conventional amplifier circuit.

[Explanation of symbols]

V ₁ , V ₂ , V _R ... Voltage source, I ₁ , I ₂ , ..., I ₈ , I
₁ ', I _2' ... current _{source, Q 1, Q 2, Q} 3, Q 4,
Q _D1 , Q _D2 , Q _D3 , Q _D4 , Q _I1 , Q _I2 , Q _I3 ... Npn type transistor, R ₁ , R ₂ , R _I1 , R _I2 , R _I3 , R _I4 ...
Resistance element, P ₁ ... Pnp type transistor, C ₁ ... Capacitor, V _CC ... Power supply voltage, GND ... Ground potential, 1 ... Supply line of power supply voltage V _CC , 2 ... Ground wire, 10, 10 a ... Input section,
20, 20a ... Current / voltage conversion unit, 30, 30a ... Output unit.

Claims (3)

[Claims] 1. A first transistor having a collector connected to a first current source and a base connected to a first voltage source, and a collector connected to a second current source and a base connected to a second current source. An input unit including a second transistor connected to a voltage source and a first resistance element connected between the emitters of the first and second transistors, and a collector of the first transistor Between the node and the first and second diodes connected in series so as to be forward from the collector toward the connection node, and between the collector of the second transistor and the connection node. Is connected between the connection node and the reference potential, and the third and fourth diodes connected in series in the forward direction from the collector to the connection node. A conversion unit composed of two resistance elements, a collector connected to a power supply, a base connected to a connection point between the first diode and the second diode, and an emitter connected to a third current source. The third transistor and the collector are connected to the fourth current source, the base is connected to the connection point between the third diode and the fourth diode, and the emitter is common to the emitter of the third transistor. An amplifier circuit having an output section including a fourth transistor connected to a third current source. 2. The amplifier circuit according to claim 1, wherein the fourth current source supplies half the current of the third current source. 3. A first transistor having a collector connected to a first current source and a base connected to a first voltage source, and a second transistor having a collector connected to a second current source. And an input section including a first resistance element connected between the emitters of the first and second transistors, and a collector and the connection node between the collector and the connection node of the first transistor. Between the first and second diodes connected in series so as to be in the forward direction toward the node, and between the collector of the second transistor and the connection node, and from the collector toward the connection node. A conversion unit including third and fourth diodes connected in series so as to be in the forward direction, and a second resistance element connected between the connection node and the reference potential. A third transistor having a collector connected to a power source, a base connected to a connection point between the first diode and the second diode, an emitter connected to a third current source, and a collector connected to a fourth transistor. A current source and a base of the second transistor of the input section, the base of which is connected to a connection point of the third diode and the fourth diode;
The fourth transistor has an emitter connected to the third current source in common with the emitter of the third transistor, and a capacitive element connected between the collector of the fourth transistor and a reference potential. A filter circuit having an output section.