JP3022388B2 - Translinear multiplier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a differential amplifier circuit, and more particularly to an OTA having a linear transconductance over a wide input voltage range.

[0002]

2. Description of the Related Art Conventionally, this type of differential circuit has been known as OTA (Oper
ational Transconductance Amplifier). O
Transconductance is linear like TA
Is also called a "translinear" circuit. Therefore, as shown in the present application, O
TA can be called a translinear multiplier because a product of the input voltage and the drive current of the differential circuit is obtained.

[0003] The present application points out that the conventional translinear multiplier described in Japanese Patent Publication No. 251385 does not operate linearly, that is, does not become a translinear multiplier, and clarifies the components for realizing a correct translinear multiplier. It is the claim of the present application.

[0004] First, a transistor model will be described. The relationship between the collector current I _{C of the} transistor and the base-emitter voltage V _BE is represented by the following equation, assuming that they follow an exponential law.

[0005]

(Equation 1) Here, _IS is the saturation current, _VT is the thermal voltage, and _VT =
It is represented by kT / q. Here, q is a unit electron charge, k is a Boltzmann constant, and T is an absolute temperature.

The base-emitter voltage V _BE is 600 mV
In the case of the front and rear transistors, the exponent part ex during normal operation
Since p (V _BE / V _T ) is a value of the order of ten, −1 can be ignored. Therefore, equation (1) is

[0007]

(Equation 2) It may be.

Next, the operation of the conventional translinear multiplier described in Japanese Patent Publication No. 251385 will be described. FIG. 5 is a circuit diagram showing a configuration of a conventional translinear multiplier.

In FIG. 5, if the transistors Q109 and Q110 are operating linearly with respect to the differential input voltage Vi, if the transconductance is set to Gm, the transistors Q109 and Q110 flow through the series diodes D101 and D104 and the series diodes D103 and D106. The currents I _A1 and I _A2 are

[0010]

(Equation 3) Further, the constant current I is supplied to the series diodes D102 and D105.
_{Since OB} is flowing, the voltage drop due to each series diode is

[0011]

(Equation 4) Therefore, the differential input voltages ΔV ₁ and ΔV ₂ to the differential circuits 12 and 14 are

[0012]

(Equation 5) Therefore, the differential output current ΔI of the two pairs of differential circuits 12 and 14 connected in parallel is

[0013]

(Equation 6) Does not work linearly.

[0014]

In analog signal processing, the OTA is an indispensable basic function block. However, the translinear multiplier described in Japanese Patent Publication No. 251385 did not operate linearly as described above.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. The most basic OTA in analog signal processing is a translinear multiplier having a wide linear input voltage range. It is intended to be realized on a semiconductor integrated circuit.

[0016]

In order to achieve the above object, a translinear multiplier according to the present invention comprises two diodes connected in series, a first series diode driven by a first input current, and , Two connected in series
A second series diode driven by a second input current and a second diode connected in series, the square root of the product of the first input current and the second input current. A third series diode driven by a current having a value, a terminal voltage of the second series diode and a terminal voltage of the third series diode as differential input voltages, and two transistors forming a differential pair A first differential circuit driven by a third input current, and a terminal voltage of the third series diode and a terminal voltage of the first series diode as differential input voltages to form a differential pair. And a second differential circuit in which one transistor is driven by the third input current.

At this time, the first input current and the second input current are differential output currents of a voltage-current converter comprising a differential circuit, and the third series diode is A diode driven by an input current of
And a transistor driven by an input current of
A sum voltage of a forward voltage of the diode and a voltage between the base and the emitter of the transistor is output.

Further, another configuration of the translinear multiplier of the present invention is configured such that a first transistor and a second transistor which are driven by a first input current and whose collector and base are connected are connected in series. A first series diode, a second series diode driven by a second input current and having a third transistor and a fourth transistor connected in collector and base connected in series, and a third input A fifth transistor driven by a current, the collector and the base of which are connected, and a fourth input current;
A sixth transistor having a base connected to the emitter of the fifth transistor, a seventh transistor having a terminal voltage of the second series diode and an emitter voltage of the sixth transistor as a differential input voltage, A first differential circuit composed of an eighth transistor, ninth and tenth transistors having a terminal voltage of the first series diode and an emitter voltage of the sixth transistor as a differential input voltage; And the emitters of the seventh transistor, the eighth transistor, the ninth transistor, and the tenth transistor are commonly connected to each other, and the fifth differential circuit
And a differential pair circuit driven by an input current of, wherein the third input current is a current a times the first input current,
The fourth input current is a current b times the second input current, and the emitter areas of the first transistor, the third transistor, the seventh transistor, and the ninth transistor are each 1 The emitter area of the second transistor and the fourth transistor is K ₂ , the emitter area of the fifth transistor is K ₃ , and the emitter area of the sixth transistor is K <sub>3
4. When</sub> the emitter area of the eighth transistor and the emitter area of the tenth transistor are K ₁ , respectively, K ₃ · K ₄ = ab · K ₁ · K ₂ .

At this time, the first input current and the second input current are differential output currents of a voltage-current converter composed of a differential circuit.

In the translinear multiplier configured as described above, three pairs of series diodes are connected to the square root of the product of two differential output currents output from the voltage-current converter and two differential output currents. Driving with equal current results in the midpoint voltage of two pairs of series diodes driven by the differential output current of the voltage-to-current converter. Therefore,
A tanh ^-1 (x / 2) -tanh (x / 2) conversion can be realized, and a translinear multiplier that operates linearly can be realized.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of a translinear multiplier according to a first embodiment of the present invention. 1, the current I _A1 flows through the series diode D1, D4, and the current I _A2 flows through the series diode D2, D5.

In the translinear multiplier of the present invention,
Is the current (I_A1・ I_A2)
^1/2To make it flow. By passing such a current,
Terminal voltage V of series diodes D3 and D6_ThreeIs a serial die
Terminal voltage V of diodes D1 and D4 ₁And series diode D
2, terminal voltage V of D5_TwoBecomes the midpoint voltage.

The terminal voltage V ₃ is divided into the terminal voltage V ₁ and the terminal voltage V.
The specific circuit to a _second midpoint voltage shown in FIG. FIG. 2 is a circuit diagram showing a configuration of a translinear multiplier according to a second embodiment of the present invention. It is assumed that the matching between the elements of the circuit shown in FIG. 2 is good.

In FIG. 2, if the VI converter 1 is operating linearly with respect to the differential input voltage Vi, the transconductance is set to Gm, and the series diodes D1, D
4, and the currents I _A1 and I _A2 flowing in the series diodes D2 and D5 are

[0026]

(Equation 7) The diode D3 has a current _IA1 and a transistor Q5.
_{Has a} current I _A2 flowing through it.
D4, series diodes D2, D5, and diode D
3 and the voltage drop V ₁ of the transistors Q5, V _2, V ₃
Respectively

[0027]

(Equation 8) Therefore, the differential input voltage ΔV for the differential circuits 2 and 4
₁ , ΔV ₂

[0028]

(Equation 9) Therefore, the differential output current ΔI of the two pairs of differential circuits 2, 4 connected in parallel is

[0029]

(Equation 10) And linearly operate.

In general, the above-described approach of the present invention, in a well-known Gilbert gain cell,
It can be derived from a method of converting each output current of the linear VI converter 1 into a voltage (tanh ^-1 ) through one diode, and performing a tanh conversion on the difference voltage as an input of the differential circuit. That is, in the tanh ^-1 -tanh conversion

[0031]

[Equation 11] Is used, but in this way

[0032]

(Equation 12) Is used. That is, a doubled difference voltage is obtained by connecting two diodes in series. Although higher by emitter voltage V _BE fraction, base generated by variations in the device - - supply voltage in the manner of the present invention is the base of the transistor offset voltage of the emitter voltage V _BE is the two diodes from fits to √2 times 1 / √2 (= 0.7
07).

It is not always easy to realize a linear VI converter. FIG. 3 shows V- shown in FIG.
The example which comprised I converter 1 using a differential circuit is shown. Although the VI converter shown in FIG. 3 cannot obtain linear VI conversion, practical voltage-current conversion characteristics can be obtained with a simple configuration.

Further, the circuit having the transfer characteristic represented by the equation (18) can be realized by a circuit in which the emitters of two differential pairs are connected in common and driven by one tail current. Such a circuit is shown in FIG.

Referring to FIG.

[0036]

(Equation 13) Also, from the tail current condition,

[0037]

[Equation 14] Solving equation (24) from equation (19) gives

[0038]

(Equation 15) Therefore,

[0039]

(Equation 16) Here, if the VI converter 3 is operating linearly with respect to the differential input voltage Vi, the transconductance is set to Gm.
In other words, the currents I _A1 and I _A2

[0040]

[Equation 17] The base voltages V ₁ , V ₂ and V ₃ are respectively

[0041]

(Equation 18) Substituting equation (29) into equation (26) from equation (27) gives

[0042]

[Equation 19] Here, in order for equation (30) to be equivalent to equation (18),

[0043]

(Equation 20) This is the condition to provide the terminal voltage V ₃ the midpoint voltage of the terminal voltage V ₁ and the terminal voltage V _2. At this time, equation (30) is

[0044]

(Equation 21) Thus, a translinear multiplier that operates linearly is obtained.

[0045]

Since the present invention is configured as described above, the following effects can be obtained.

The first effect is that an OTA that operates linearly can be realized.

The reason is that the common applied voltage of the differential circuits connected in parallel is the midpoint voltage.

The second effect is that the influence of the offset voltage of the base-emitter voltage V _BE of the transistor, which is caused by the variation of the elements, can be reduced.

The reason is that two diodes are connected in series.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a translinear multiplier according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a translinear multiplier according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a translinear multiplier according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a translinear multiplier according to a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a conventional translinear multiplier.

[Explanation of symbols]

 1,3 VI converter 2,4 Differential circuit D1-D7 Diode Q1-Q18 Transistor R Resistor RL Load resistance

Claims (5)

(57) [Claims] 1. A first series diode comprising two diodes connected in series and driven by a first input current, and a second series diode comprising two diodes connected in series and driven by a second input current And a second series diode connected in series, and two diodes connected in series.
A third series diode driven by a current having a value equal to the square root of the product of the input current and the second input current, and a terminal voltage of the second series diode and a terminal voltage of the third series diode. A first differential circuit in which two transistors forming a differential pair are driven by a third input current as a dynamic input voltage; a terminal voltage of the third series diode and a terminal of the first series diode And a second differential circuit in which two transistors forming a differential pair are driven by the third input current, wherein the voltage is a differential input voltage. 2. The translinear according to claim 1, wherein the first input current and the second input current are differential output currents of a voltage-current converter including a differential circuit. Multiplier. 3. The third series diode includes: a diode driven by the first input current; and a transistor driven by the second input current. 3. The translinear multiplier according to claim 2, wherein a sum voltage with a voltage between the base and the emitter of the transistor is output. 4. A first series diode driven by a first input current and having a first transistor and a second transistor connected in collector and base connected in series; and A second series diode that is driven and has a third transistor and a fourth transistor connected in series with a collector and a base, and a second series diode that is driven with a third input current and has a collector and a base connected. A sixth transistor driven by a fourth input current and having a base connected to the emitter of the fifth transistor; a terminal voltage of the second series diode and an emitter of the sixth transistor A first differential circuit composed of a seventh transistor and an eighth transistor having a differential input voltage as a differential input voltage, and a terminal voltage of the first series diode. And a second differential circuit including a ninth transistor and a tenth transistor, each of which has a differential input voltage based on the differential input voltage and an emitter voltage of the sixth transistor. A differential pair circuit in which emitters of the ninth transistor and the tenth transistor are connected to each other in common and driven by a fifth input current; The first input current, the third transistor, the seventh transistor, wherein the current is a times as large as the first input current, and the fourth input current is b times as large as the second input current. and the ninth emitter areas of the transistors respectively as 1, the respective K ₂ the emitter area of the second transistor and the fourth transistor, the fifth transistor The emitter area K of
₃ , when the emitter area of the sixth transistor is K ₄ , and the emitter areas of the eighth transistor and the tenth transistor are K ₁ , respectively, K ₃ · K ₄ = a · b · K ₁ · K _2. A translinear multiplier, which is ₂ . 5. The translinear according to claim 4, wherein the first input current and the second input current are differential output currents of a voltage-current converter including a differential circuit. Multiplier.