JPS63159986A - Multiplier - Google Patents

Abstract

PURPOSE:To reduce a carrier by constituting the titled multiplier so that even if a difference is generated in an output current, its difference is detected by a current detecting part, and corrected and corrected by a current correcting part. CONSTITUTION:To transistors Q1, Q2 for executing a differential amplification, an input signal Vin is supplied,and to each collector, output current I1, I2 flow. For instance, in case of I1>I2, a voltage drop portion of a resistance R1 becomes larger than a voltage drop portion of a resistance R2, a transistor Q11 of a current detecting part 2 operates to an ON state, and a current I3 increased. When the current I3 increases. When the current I3 increases, a suction quantity of the current I2 by a transistor Q14 of a current correcting part 3 becomes large, and the current I2 for driving the transistors Q6, Q7 of a multiplying part 1 is controlled so as to become large, and becomes the same current as the driving current I1 of the transistors Q4, Q5. In this state, the transistors Q4-Q7 to which a carrier signal f1 is supplied operate under the same condition, and a carrier leak is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multiplier that obtains an output signal proportional to the product of two input signals. Concerning circuit technology that is effective when applied to.

[Conventional technology]

Analog multipliers, also called analog multipliers, are well known among those skilled in the art, and are widely used in stereo demodulation circuits, various video equipment, and the like.

An example of the above-mentioned multiplier is the "analog integrated circuit" (Showa 57
4th edition published on February 1st, Publisher: Kindai Kagakusha, pp236
~237). The outline is that a differential circuit is constructed in which a first input signal is supplied to the bases of a pair of transistors connected to a differential pair, and a second input signal is commonly supplied to the collectors of each of the pair of transistors. It was established.

The inventor of the present invention conducted studies to reduce the carrier drift appearing in the output signal of the multiplier. The following is a technology considered by the present inventor, although it is not a publicly known technology, and its outline is as follows.

That is, referring to the above-mentioned known example, in many cases, (1) is a carrier signal, and (2) is an input signal to be multiplied, and the inventor's study revealed that the carrier component is likely to leak into the output signal Vo (carrier leak). It was revealed.

[Problem that the invention seeks to solve]

When the inventor investigated the cause of the leakage of the Yayaria signal, the cause became clear. That is, referring to the above-mentioned known example, when the output currents Is, Is of the transistors T, , T, are 1. 〆When it reaches I6, the output signal Vo
Carrier leak occurs. The relationship between the above-mentioned step and finish 6 occurs due to variations in the characteristics of the transistors T6 and Ts, as well as variations in the input resistance, and it is difficult to eliminate these variations.

Therefore, the inventor of the present invention has developed and completed the construction using circuit technology.

The present invention was proposed based on the idea that the above carrier leakage could be reduced by correcting the relationship.

An object of the present invention is to provide a multiplier that can reduce carrier leakage.

The above and other objects and novel features of the present invention will become apparent from the present specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this book is as follows.

That is, the second and third differential amplifiers are provided at the output terminals 1, for example, the collectors of each of the pair of transistors constituting the first differential amplifier, and the first input signal is supplied to the first differential amplifier. , the second and third differential amplifiers
input signals are commonly supplied. Furthermore, a current detecting section that obtains a control signal corresponding to the difference between the detected current flowing through the collector (output current) '%' and a current correcting section that corrects the current flowing through the collector based on the control signal is provided. It is something that

[For production]

According to the above-mentioned means, even if a difference occurs in the collector current (output current) due to equal voltage characteristic variations of the pair of transistors constituting the first differential amplifier, the difference is detected by the current detection section and the current correction is performed. Since the second and third differential amplifiers that perform the multiplication operation are driven under almost the same conditions, one of the causes of carrier leakage can be solved, and the multiplier can be corrected by reducing carrier leakage. can be obtained.

〔Example〕

Hereinafter, one embodiment of a multiplier to which the present invention is applied will be described with reference to FIGS. 1 and 2. Note that FIG. 1 is a circuit diagram of a multiplier integrated into an IC, and FIG. 2 is a frequency characteristic diagram of a control signal for explaining the circuit operation.

In multiplication section I, transistors Q1-Qt perform differential amplification, and transistors Q*-Q*reference voltage Vref
, resistor Rs -Re constitute a constant current circuit. The transistors Qt and Qt receive one input signal Vi in the present invention.
n is supplied, and each collector is supplied with an output current I as used in the present invention.
,,I, flows.

The resistors R, ,R, have the same resistance value and are used to perform current-voltage conversion and detect the current difference between the output currents X, ,I. Then, a voltage corresponding to the current difference is supplied to a current detection section 2, which will be described later.

On the other hand, the transistor Q4*Qss and the transistors Q. and QtK are supplied with the carrier signal f.

Then, an output signal Vout, which is the product of the input signal V in and the carrier signal f1, is obtained from the load circuit RL.

In the multiplier shown in this embodiment, the most important circuit operations are performed by the current detection section 2 and the current correction section 3.

That is, assuming that the output currents I, , I, are L>It, the voltage drop across the resistor R8 is greater than the voltage drop across the resistor R3. As a result, the base voltage of the transistor Qtt in the current detection section 2 changes from the base voltage of the transistor Q1.
lower than the base voltage of Transistor Q11 operates in the on state, and the current flow rate increases. The electric current corresponds to an increase in the output current 11, and corresponds to the control signal in the present invention.

The transistor Qss of the current correction section 3 is connected to the reference voltage Vref.
The bias voltage and base current of transistor Qsz are controlled by the current generator. As described above, as the current I increases, the amount of current I absorbed by the transistor Qt4 increases. As a result, the transistor Q of the multiplier 1
The current that drives s = Qy (output current L) is controlled to a large value and becomes the same current as the drive current of transistors Q4-Qs, that is, the output current. The transistors Q, -Q to which the carrier signal f1 is supplied operate under the same conditions, and carrier leakage is reduced.

When performing the series of correction operations described above, the current detection section 2 performs the correction operations satisfactorily with the following characteristics.

That is, assuming that the emitter resistances of the transistors Q tt s Q tt are the same,
The transconductance gm of the transistor Qll*Qtt is determined by gm=1/re. transistor Q
A capacitor C that determines frequency characteristics is connected to the collector of tt, so that it has a gain and a frequency characteristic determined by the capacitor C. The fact that the current detection section 2 has a high gain means that even if the voltage drop across the resistors R, , R, is minute, the current correction section 3 can be driven to perform the current correction with high accuracy.

Also, by selecting the capacitance of capacitor C, the frequency a
As the characteristics are shown in FIG. 2, a low frequency faK can be set with respect to the frequency of the carrier signal f1, and current correction can be performed without being influenced by the carrier signal f.

The circuit operation when the output current 11 increases has been described above, but when the output current 11 increases, the following operation is performed.

That is, as the output current increases, the resistance R1
voltage drop becomes large. Transistor Q of current detection circuit 2 operates in an on state, and current I4 increases. This electric current corresponds to the output current I2, and corresponds to the control signal in the present invention. Transistor Q11#
Qt- is connected to the current mirror and transistor Q
The transistor QtsK bias voltage is supplied by saK, and the transistor Q1s also sinks current from the capacitor C.

The terminal voltage of capacitor C, i.e. transistor Q14
The pace voltage gradually decreases.

However, the bias voltage of transistor Qsa is.

Since it is held at Vref, the sinking of the output current 1 by the transistor Q14 is reduced, and the sinking of the output current 11 by the transistor Q□ increases accordingly.

As a result of the above circuit operation, transistor Q4-
The electric current 51 that drives Qs and Q・, Qy! (output current I,
, I,) is corrected, and carrier leakage can be reduced. In this case as well, the gain and frequency characteristics of the current detection section 2 are determined in the same manner as described above.

The multiplier shown in the above embodiment has the following effects.

(11) A first differential amplifier to which a first input signal is supplied, and a second and 3 differential amplifiers are provided to constitute a multiplication section, and a current detection section that detects the current difference between the output currents flowing through each of the collectors to obtain a control signal, and Since a current correction section for correcting the difference is provided, it is possible to drive the second and third differential amplifiers under the same conditions by correcting the output current.

(2) The above (1) provides the effect of reducing the leakage of the second input signal contained in the output signals obtained from the second and third differential amplifiers.

(3) Since the gain of the current detection section is increased, the current correction can be performed with high sensitivity and accuracy.

(41) By forming a frequency characteristic in the current detection section that can remove the frequency component of the second input signal, an effect can be obtained that the current correction can be performed without being influenced by the frequency component.

(5) Since the allowable value of the input offset voltage of the transistors constituting the first differential amplifier becomes large, the input circuit D
It becomes possible to connect directly to C, increasing the added value of IC.

Above, the invention made by the present inventor has been specifically explained based on examples, but the present invention is not limited to the above examples, and it is understood that various changes can be made without departing from the gist of the invention. Needless to say.

For example, although not particularly shown, the load R1 may be a resistor, a load, a load circuit using a transistor, or the like.

In the above explanation, the invention made by the present inventor was mainly applied to a multiplier, which is the field of application that formed the background of the invention. The present invention can be widely used in video equipment such as a VTR.The present invention can be used at least in ICE which requires a multiplier.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, a first differential amplifier is supplied with a first input signal to be multiplied, and a second input signal driven by two output currents of the first differential amplifier is commonly supplied with a second input signal to be multiplied. A multiplication unit is constructed by combining the second and third differential amplifiers, and the above-mentioned output.

A current detection section that detects an error in the force sensation flow, and a current correction section that corrects the error in the second output current using a control signal obtained from the current detection section, and the second and third output currents are corrected by correcting the output current. The differential amplifiers are driven under the same conditions to reduce the frequency components of the input signal that leak into the multiplied output signal.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a multiplier to which the present invention is applied, and FIG. 2 is a frequency characteristic diagram illustrating the circuit operation. DESCRIPTION OF SYMBOLS 1... Multiplication part, 2... Current detection part, 3... Current correction part, Q1-Q1s... Transistor, R1 to R8.
...Resistance, C...Capacitor, ■, ~I4...Current, Vin...Input signal, 1st wJ L----J Fig. 2

Claims (1)

[Claims] 1. A current detection unit that detects the output current of a pair of transistors to which one input signal is supplied among the two input signals to be multiplied and obtains a control signal with a desired frequency characteristic; a current correction section that corrects the error of
A multiplier characterized by each of the following.