JP2856127B2 - Differential conductance circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a differential conductance circuit, and more particularly to a differential conductance circuit that converts a differential input voltage into a current and outputs the current.

[0002]

2. Description of the Related Art A conventional differential conductance circuit of this kind (also referred to as a "transconductance amplifier") receives an input signal via terminals 1 and 2 and converts it into a current as shown in FIG. A first differential circuit 12 for outputting,
A load transistor pair 13 receiving an output current of the first differential circuit 12, a second differential circuit 14 receiving a voltage generated in the load transistor pair 13, converting the voltage into a current, and outputting the current to terminals 3 and 4; And first and second constant current sources 10 and 11 for receiving a bias voltage via the first and second constant current sources 6 and supplying constant currents I ₃ and I ₂ to the first and second differential circuits 12 and 14, respectively. ing. Terminals 5 and 7 are connected to a power supply and a ground, respectively.

The first differential circuit 12 has a third and a fourth circuit in which a series circuit of _third and _fourth resistors R ₃ and R ₄ (also referred to as “emitter resistors”) having the same resistance value is connected between the emitters. Fourth transistors Q ₃ and Q ₄ , and third and fourth resistors R ₃ ,
The output of the first constant current source 10 is connected to the common connection point of R ₄ , and the collectors of the third and fourth transistors Q ₃ and Q ₄ forming a differential pair form a load transistor pair 13. Fifth and sixth transistors Q ₅ , which are diode-connected,
It is connected to the emitter of Q _6.

The emitters of the fifth and sixth transistors Q ₅ and Q ₆ are connected in common (directly connected) to the bases of _seventh and _eighth transistors Q ₇ and Q ₈ constituting a second differential circuit. Connected to each other.

The output of the second constant current source 11 is connected to the common connection point of the emitters of the seventh and eighth transistors Q ₇ and Q ₈ , and the output of the seventh and eighth transistors Q ₇ and Q ₈ The collectors are connected to terminals 3 and 4, respectively.

The first constant current source 10 has a first transistor Q ₁ having one end connected to the emitter of the first resistor R ₁ and having the collector outputting a constant current.

The second constant current source 11 has a second transistor Q ₂ having an emitter connected to one end of a _second resistor R ₂ and having a collector outputting a constant current.

The bases of the first and second transistors Q ₁ and Q ₂ are commonly connected to a terminal 6, and the first and second resistors R ₁ and R 2
The other end of R ₂ is commonly connected and grounded via terminal 7.

[0009] Then, the emitter area of the second transistor Q ₂ is, N of the first emitter area of the transistor Q ₁
Times (where, N> 0) is set to the resistance value of the second resistor R ₂ is set to 1 / N times the first resistance value of the resistor R _1.

The operation of the conventional differential conductance circuit shown in FIG. 6 will be described below.

The conductance (mutual conductance) when the input signal voltage supplied to the terminals 1 and 2 is output as a current from the terminals 3 and 4 is, as a whole, the conductance g _{m1 of} the first differential circuit 12 and the load Transistor pair 1
The product is the product of the parallel combined resistance R _L of the input impedances of the third and second differential circuits 14 and the conductance g _{m2 of} the second differential circuit 14. The grounded emitter current gains of all the transistors are equal to β, so that g _m1 , R _L , g
_m2 is given by the following equations (1) to (3). However,
V _T is the thermal voltage (approximately at room temperature 26 mV) (V _T = kT /
q and k are Boltzmann's constant, T is absolute temperature, and q is unit charge of electrons).

[0012]

(Equation 1)

[0013]

(Equation 2)

[0014]

(Equation 3)

[0015] and the output current I ₃ of the first constant current source 10, the output current I ₂ of the second constant current source 11, the emitter area of the second transistor Q ₂ is the emitter area of the first transistor Q1 N times, the value of the _second resistor R ₂ is equal to the value of the first resistor R ₁
Is 1 / N times the value of, the following equation (4) holds.

I ₂ = NI ₃ (4)

When the above equations (1), (2) and (3) are multiplied and rearranged using the above equation (4), the overall conductance g
_m0 is given by the following equation (5).

[0018]

(Equation 4)

Normally, the value of the ground emitter current amplification factor β is several tens to several hundreds, so the above equation (5) is approximately expressed by the following equation (6).

[0020]

(Equation 5)

Here, (2N + 1) / β << 1, R ₃ >>
> 2V _T / I ₃ , the overall conductance g
_m0 is approximately proportional to N.

That is, the entire conductance of the differential conductance circuit shown in FIG. 6 is set so as to be substantially proportional to the output current ratio of the first and second constant current sources 10 and 11.

[0023]

In the conventional differential conductance circuit INVENTION SUMMARY is], the output current I ₂ of the first of the second constant current source 11 with respect to the output current I ₃ of the constant current source 10 to the conductance and large Is large, the coefficient (2N + 1) multiplied by 1 / β in the above equation (6) indicating the conductance becomes large, so that the conductance is strongly affected by the common emitter current amplification factor β of the transistor. Will be.

[0024] Using the above equation (5) showing the overall conductance g _m0, the change of the conductance g _m0 of the whole case of the emitter grounding current amplification factor of the transistor beta is changed from 50 to 200, of beta = 100 FIG. 7 shows the conductance value at the time, which is normalized so as to be the reference “1”.

FIG. 7 shows the case where N = 1, 2, and 3. As can be seen from FIG. 7, N (N = I ₂ / I ₃ ,
I ₃ is the output current of the first constant current source 10, and I ₂ is the larger the output current of the second constant current source 11, the greater the rate of change in conductance.

Therefore, particularly when N is set to be large, there is a problem that the conductance g _m0 greatly varies due to the variation of the common emitter current gain β of the transistor.

The present invention has been made in view of the above problems, and has a common emitter current amplification factor β of a transistor.
It is an object of the present invention to provide a differential conductance circuit that prevents a variation in conductance due to the variation in the above.

[0028]

In order to achieve the above object, the present invention provides a first differential circuit having a transistor pair whose emitter is connected via a resistor, and an output of the first differential circuit. A second differential circuit having a load transistor pair connected to the first transistor, a transistor pair having a base connected to the load transistor pair and an emitter connected in common, and a current flowing through the first differential circuit. A first constant current source for supplying current, and a second constant current source for supplying current to the second differential circuit, wherein the first constant current source comprises: An emitter-grounded circuit having a first transistor whose emitter is grounded via a first resistor;
Is configured as a common emitter circuit having a second transistor whose emitter is grounded via a second resistor, and the base of the first transistor is a third emitter.
And the resistance of the second resistor is 1 / N (where N is a predetermined positive number) times the resistance of the first resistor. And the second transistor of the second constant current source
Is an emitter of the first transistor of the first constant current source.
A third conductance circuit having an emitter area N times the area of the first resistor, and wherein the third resistance is set to a resistance value slightly larger than 2N + 1 times the resistance value of the first resistance. provide.

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a differential conductance circuit according to one embodiment of the present invention. In FIG. 1, elements having the same functions as those in FIG. 6 referred to for explanation of the conventional differential conductance circuit are denoted by the same reference numerals, and hereinafter, the same elements as those in the conventional differential conductance circuit will be described. The description of the parts will be omitted, and only the differences will be described.

Referring to FIG. 1, the base of the first transistor Q1 of the first constant current source 10 is connected to a fifth resistor R5.
Is connected to the terminal 6 together with the base of the second transistor Q2 of the second constant current source 11. Then, the value of the fifth resistor R5 is set to 2N + 1 times the first resistor R1 by the ratio N of the first resistor R1 and the second resistor R2. Note that, similarly to the above-described conventional differential conductance circuit, the resistance value of the second resistor R2 of the second constant current source 11 is 1 / N of the resistance value of the first resistor R1 of the first constant current source 10.
It is assumed that the output current I2 of the second constant current source 11 is N times the output current I1 of the first constant current source 10. At this time, the emitter area of the second transistor Q2 of the second constant current source 11 is set to N times the emitter area of the first transistor Q1 of the first constant current source 10.

The operation of the embodiment shown in FIG. 1 will be described below. The base current of the first transistor Q ₁ constituting the first constant current source 10 causes a voltage drop at a fifth resistor R ₅ connected between the base of the first transistor Q ₁ and the terminal 6. Output current I of the first constant current source 10
₁ is smaller than the output current I ₃ (see FIG. 6) when the fifth resistor R ₅ is not provided.

The value of the output current I ₁ of the first constant current source 10 in the present embodiment, the output current I ₃ when the resistor R ₅ of the fifth is not provided, the first resistor R ₁ and the 5 resistor R ₅
And 2N + 1, and β of the first transistor Q ₁ .

[0034]

(Equation 6)

Further, the following equation (8) is derived from the relation of the above equation (4).

[0036]

(Equation 7)

As the conductance of the differential conductance circuit according to the present embodiment, the above equations (1), (2), and (3)
By replacing all the currents I ₃ in I with I ₁ and using the relationship of the above equation (8), the following equation (9) is obtained.

[0038]

(Equation 8)

Since the grounded emitter current gain β is β >> 1, approximating the above equation (9) yields the following equation (10).

[0040]

(Equation 9)

From the above equation (10), the coefficient of β ^-1 is 0 in the entire conductance g _m0 , and the effect of the ground emitter current amplification factor β on the conductance can be extremely reduced. to take actually finite values of 50 to 200 is beta, the value of the resistor R ₅ ideal fifth,
It is slightly larger than 2N + 1 times the first resistor R ₁ , and N =
In the case of 1, 2, and 3, values are substantially as shown in the following (11) to (13).

N = 1: R ₅ = 3.2 · R ₁ (11)

N = 2: R ₅ = 5.7 · R ₁ (12)

N = 3: R ₅ = 8.5 · R ₁ (13)

The changes in conductance when N = 1 and N = 3 are shown in FIGS. 2 and 3, respectively. 2 and 3 both normalize the conductance with the value of the common emitter current amplification factor β = 100, and for comparison, the case where the fifth resistor R ₅ = 0 (the fifth resistor R ₅ is not provided) ) Is also shown.

From FIG. 2 and FIG. 3, the fifth resistor R ₅ is
(2N + 1) · With slightly larger than R _1, β
It can be seen that the effect on the conductance of the above can be reduced.

Next, the configuration of a differential conductance circuit according to another embodiment of the present invention is shown in FIG.

Referring to FIG. 4, this embodiment is different from the first embodiment shown in FIG. 1 in that the output of the second differential circuit 14 is connected to ninth and tenth transistors Q ₉ , Q ₁₀ The signal is output via a common base amplifier circuit composed of This embodiment, the even stronger than in the first embodiment, due to the influence of the grounded emitter current amplification factor beta, optimum value of the resistance R ₅ of the fifth, the fifth resistor of the first embodiment R ₅
When N = 1, R ₅ = 4.4R ₁ is optimal.

FIG. 5 shows the change in conductance in this case. In FIG. 5, as in FIGS. 2 and 3, β = 1
The conductance is normalized by the value of 00, and the change when the _fifth resistor R ₅ = 0 is also shown for comparison.

[0050] In this embodiment, the base-grounded amplifier circuit 15 connected to the output of the second differential circuit 14, the conductance further influenced by the extra β, but the value of the fifth resistor R ₅ suitable By setting to, the change in conductance can be reduced as in the first embodiment shown in FIG.

[0051]

As described above, according to the present invention,
A first differential circuit consisting of a transistor pair connecting a resistor between the emitters, a load transistor pair connected to the output of the first differential circuit, and a base connected to the load transistor pair and the emitter directly connected. A second differential circuit composed of a transistor pair; a first constant current source connecting an output to the first differential circuit; and a second constant current source connecting an output to the second differential circuit Wherein the first constant current source is a grounded emitter circuit that grounds an emitter via a first resistor and connects a second resistor to a base, wherein the second constant current source comprises: An emitter grounding circuit for connecting an emitter to ground via a third resistor and connecting a base to the other end of the second resistor, wherein the third resistor is 1 / N times the first resistor. Set up,
By setting the second resistor to 2N + 1 times or more of the first resistor, it is possible to reduce the variation in the conductance of the entire circuit due to the variation in the common emitter current gain β of the transistor.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a rate of change in conductance in one embodiment of the present invention.

FIG. 3 is a diagram showing a rate of change in conductance in one embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of another embodiment of the present invention.

FIG. 5 is a diagram showing a rate of change in conductance in another embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a conventional differential conductance circuit.

FIG. 7 is a diagram showing a rate of change in conductance of a conventional differential conductance circuit.

[Explanation of symbols]

Q _{1 to} Q ₁₀ transistors R _{1 to} R ₅ resistors 1 to 8 terminals 10 first constant current source 11 second constant current source 12 first differential circuit 13 load transistor pair 14 second differential circuit 15 base Ground amplifier circuit

Claims (3)

(57) [Claims] 1. A first differential circuit having a transistor pair having an emitter connected via a resistor, a load transistor pair connected to an output of the first differential circuit, and a base connected to the load transistor pair. , A second differential circuit having a transistor pair having an emitter connected in common, a first constant current source supplying current to the first differential circuit, and a second differential circuit. And a second constant current source for supplying a current to the driving circuit. The first constant current source comprises a first constant current source having an emitter grounded via a first resistor. The second constant current source is configured as a common emitter circuit having a second transistor whose emitter is grounded via a second resistor, The base of the first transistor is connected to the base of the second transistor via a third resistor, and the second resistor has 1 / N of the resistance of the first resistor.
(Where N is a predetermined positive number) times the resistance value, and the second transistor of the second constant current source is connected to the second transistor.
The emitter area of the first transistor of one constant current source
A differential conductance circuit having an emitter area N times as large as that of the first resistance, and wherein the third resistance is set to a resistance value slightly larger than 2N + 1 times the resistance value of the first resistance. 2. The load transistor pair according to claim 1, wherein said load transistor pair is diode-connected, and comprises a transistor pair inserted between a collector and a power supply of the transistor pair of said first differential circuit. The described differential conductance circuit. 3. The differential conductance circuit according to claim 1, wherein an output signal of said second differential circuit is output through a grounded base amplifier circuit.