JPS5880916A - Interface circuit - Google Patents

Abstract

PURPOSE:To apply a process of manufacturing an integrated circuit with low dielectric strength to one interface circuit, and to realize reduction in chip area and economization, by applying current coupling to an information coupling means from one side to the other. CONSTITUTION:The input SIGi of an interface circuit INT is connected to one input of a control circuit CONT, whose output is connected to the input CPUi of a coupling means CPU; and the output CPUo of the coupling means CPU is connected to the input CSi of a current generating means CS, whose one output CS01 is connected to the output SIGo of the interface circuit INF while the other output CS00 is connected to the other input of the control circuit CONT. The control circuit CONT executes a comparison between those two input signals, i.e. SIGi and CS00 and performs control to obtain coincidence between both of them, so both inputs are in proportion to each other in a balanced state and both outputs CS01 and CS00 of the current generating means CS have proportional relation, so that the inputs SIGi to the interface circuit INF and the output SIGo are in proportion to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an interface circuit for transmitting information between two points having different characteristics, ToD, 41
The present invention relates to an interface circuit suitable for nonlithically integrated circuits.

Conventionally, transformers have been used in this type of circuit, but since Jin's transformer is composed of an iron core and wire rings, it has the disadvantage that it cannot be made smaller.

On the other hand, there are some studies on converting this type of circuit into electronic circuits), for example, Technical Research Report of the Institute of Electronics, Electronics and Communications Engineers 5E79-107゜Hita, Hamasato: [11L Various Forms of Subsidiary Subscriber Tsukuda and Somesome Evaluation J
There is an optical coupling method and a current coupling method as shown on January 22, 1980, but the former requires a highly symmetrical optical coupling element, and the latter requires a high-voltage transistor in the coupling part. When the opposing interface circuits are monolithically integrated, the production of both circuits requires high-voltage processing, which has the disadvantage of increasing the chip area.

In order to eliminate these drawbacks, the present invention applies a first current mirror to transmit information from the other side to one side, and uses an optical coupling element to transmit information from one side to the other side. A second current mirror is provided on one side to which an element having a voltage resistance or an insufficient 4I characteristic is applied, and the influence of the nonlinearity of the optical coupling element or an element having an insufficient characteristic is applied. The purpose of this is to make it possible to apply a low-voltage integrated circuit fabrication process to one side of the interface circuit, thereby achieving miniaturization and economical chip area. The invention will be explained below with reference to the drawings.

FIG. 1 shows a first embodiment illustrating the principle of the present invention.
Gi is the input of the interface circuit, 5IGo is the output of the interface circuit, CS is the current generating means, and C5i
is input, C8,. and CS0. are the output and CUP, respectively.
is a coupling means, CUPi is an input, and CUPo is an output.

Next, to explain the connection, the input 5IGi of the interface circuit INF is connected to one input of the control circuit C0NTO,
The output of the skeleton control circuit C0NT is the input CU of the coupling means cvp.
The output cvp of the coupling means CUP is connected to Pi.

is connected to the input C5i of the current generating means CS, and one output C of the current generating means C5 is connected to the interface circuit IN.
F's output SIG, connected to the other output CS,. is connected to the other input of the control circuit C0NT. Next, to explain the operation, the control circuit C0NT receives the two input signals, namely BIG,
and CS0°, and control is performed so that the two are in a matching relationship. Therefore, in an equilibrium state, both inputs are proportional, and both outputs of the current generating means CS, cs0. , cso. have a proportional relationship. Therefore, the input 5IGi and the output 5IG0 of the interface circuit INN have a proportional relationship regardless of the characteristics of the coupling means CUP.

FIG. 2 shows a second embodiment of the present invention, in which CM1 to CMS
is a current mirror, the terminal marked with a circle is the input terminal, the numbers represent the input/output ratio, P and N represent the type, O
PA is the operational amplifier, RLI RLfl is the load resistance for converting current output to voltage output, RIMI is the resistance for converting voltage input to current, Rf is the load resistance of the feedback circuit, V□nt, Ftxz are the input voltages ,r,. ! I VOT
JTt is the output voltage, Vo is the power supply voltage of the high voltage circuit, Vl
is the power supply voltage of the low-voltage circuit, E and G are the earth, and r% is the earth E.
, G, 11 to r are circuit currents, and pco is a photocoupler. The power supply for the operational amplifier OPA is not shown.

Figure 3 shows an example of a specific configuration of a current mirror.
(- is an N-type current mirror)<9-1 (6) is a P-type current mirror, and (O) is a multi-output type current mirror 2-.

Next, the operation will be explained with reference to FIG. Current $2- is a circuit that generates an output current proportional to the input voice.
The structure and operation of that is, for example, Tsunoda-! I [Basic Circuit of Analog IC 155 January 20, Published by Tokyo Electric University, 25
Since this is a well-known technique as shown on pages 26 to 26, its explanation will be omitted.

First, the input voltage r□0. from the output voltage r. . 1. We will explain the information transmission in this direction. Input voltage V□8. When is applied, R□, 1 has a circuit current! , flows, and its value is 1.7 (ignoring the voltage drop of the current mirror CM).
r. Flow into input, current! The above input current is applied to the output of F-CH2! , that is, the circuit current I
A circuit current Im equal to , flows. The circuit current 1 is the terminating resistor RL! The current flows to the terminal resistor RL! A voltage drop is generated across both ends of the output voltage, resulting in an output voltage of 0UTI.In this embodiment, the current mirror CM and CM ratio is set to 1:1, so the circuit itt flow 11*I snow s1m is All are equal, so the output voltage V.tlTl and the input voltage r
A linear relational expression is established between 8 and 1.

'Vou, rz = Is XRIJ = It XRL
, 2 = CCVa-Vxy1) XRIJ) Vo at this ζ
If is a constant voltage, then the output voltage is V. . , 1 is proportional to the input voltage ``INI'', from ro to r.

information transmission can be achieved. In addition, the input voltage r□岨 and output
force voltage r. . 7. The polarity of is reversed and a DC component is generated in the output due to the influence of O and V, but for the former, if necessary, Ayachi's phase inversion circuit can be added, and the phase inversion circuit is For example, various circuits can be applied, including an inverting amplifier using an operational amplifier, as shown in FIG. 9 on page 274 of "Transistor Technology", December 1980 issue, and a method for eliminating the latter effect will be described later.

Next, in the reverse direction, that is, input voltage r □ yo, to r. . 1. Regarding information transmission in the direction of #R,F! A, then the input voltage V
When □ is applied to the operational amplifier OPA, when the gain of the operational amplifier OPA is expressed as A, a voltage multiplied by 1 appears at the output of the operational amplifier OPA, and a circuit current of 1. supply. Since the optical coupling element PC has the characteristic that the output current changes in response to the input current, the circuit current! −, the scissors circuit current! , is a current mirror commercial.

A circuit current proportional to #mirror ratio is input to each output of the current mirror CM. , Ig flows. Circuit current! , is applied to the negative input terminal of the operational amplifier OPA and is further terminated to the earth E through the feedback resistor Rf, so that the voltage at the negative input terminal of the operational amplifier OPA is the circuit current! , and the feedback resistance Rf. Since the direction of increase and decrease is the same as the direction of increase and decrease of the input voltage VxNM, negative feedback results. Here, if the gain A of the operational amplifier OPA is sufficiently large, the positive input terminal and negative input terminal voltages r□ of the operational amplifier OPA are The current is proportional to . Current mirror CX, circuit current! , and 1. Since there is a 1:N relationship between the two output currents corresponding to and further load resistance R
If terminated at L1, an output voltage r.U'F! proportional to the input voltage "112" can be obtained. -Here, the transfer efficiency β of the optical coupling element pc and the mirror ratio from the input of the current mirror CM1 to both outputs are feedback Although related to the total gain of the loop,
By setting the value of the gain A of the operational amplifier OPA to a sufficiently large value, it is possible to suppress the effect to an easily negligible degree (6J), which is a general property of conventional negative feedback circuits. This is a well-known matter.

As is clear from the above explanation, the input voltage r.

from the output voltage r. The information transmission path in the direction of uT2 is separated by an optical coupling element pc, and the voltage across the feedback resistor Rf is equal to the input voltage 'IN! is equal to Also, current mirror C
The input side of Ms is equivalent to the forward direction characteristic of a diode.
Therefore, the input potential of the current mirror CM is approximately equal to the power supply voltage r, so the circuit portion on the low voltage side shown in FIG. 2 can be constructed without using any high voltage elements.

In the above explanation, from the input voltage FIND "0LlT2
Although we have shown an example in which an optical coupling device is applied to information transmission in the direction of , since the present invention has the feature of being able to eliminate the influence of the transfer efficiency of the coupling part, even if a current mirror is constructed using the transistor with the insufficient characteristics and is replaced with the optical coupling element, the result is the same as in the first embodiment. It is a tortoise that can provide the following effects. The third example shows a current mirror configured using a transistor with insufficient loss characteristics.
An example of this is shown in FIG. Here, C in Figure 4
M is a current mirror 2- using a transistor with insufficient characteristics in place of the above-mentioned photocoupler.

Since the operation can be easily understood from the second embodiment, the explanation will be omitted.

FIG. 5 shows a fourth embodiment, in which a plurality of detailed improvements have been added to the first and second embodiments, which will be sequentially explained below.

The first improvement is based on the 19th operational amplifier OPA, in which the input of the optical coupling element and current mirror 2- has voltage vs. current characteristics similar to the order and direction characteristics of a diode, and the resistance value decreases rapidly above a certain voltage. Although there is a possibility that an excessive current may flow in, this is limited to a predetermined value or less by inserting a resistor R81 in series. The second improvement is that a clamp diode I'01 is added as a protection against the case where the input of Karen)<2- is reverse biased.

The fifth improvement is to add means for clamping so that the voltage across the feedback resistor Rf does not exceed the withstand voltage on the low withstand voltage side.The clamp circuit includes, for example, the clamp diode DOR and the clamp diode DOR shown in FIG. can be configured by the power supply voltage V that determines i and the clamp voltage, and ymI,
Furthermore, as the power supply voltage V and rlI, it is possible to use the power supply used in the low voltage circuit such as the operational amplifier OPA.

The fourth improvement is that, due to the low impedance of the diode clamp circuit when clamping, an excessive current flows through the clamp circuit during clamp operation, but it can be reduced to a predetermined value by inserting current limiting resistors Ra2 and R□. It is limited to the following.

FIG. 6 shows a fifth embodiment, in which r is caused by the influence of ro described in the first embodiment. . ? This is related to a method for removing the DC component of Current used for the subtraction 1.
1 can be determined by the power supply voltage y, I and the resistance RIII'.

fjlf, Figure 7 shows the sixth embodiment, and the output voltage r in the fifth embodiment. This eliminates the need for power supply voltages r and I for generating the current 1.1 used for subtraction used to remove the DC component in υ, 1. The operation will be described below. The current mirror CM has a multi-output configuration with mutually equal circuit currents 1. and 1.1, and '1' self-closes. Square circuit current! , and 1.1 consist of a DC component generated by the power supply voltage V and an AC component generated by the input voltage FXMI, so one circuit current! .

AC component 11. , is shunted by the capacitor Cd1 so that only the DC component bda is input to the current mirror CM. Therefore, the current killer commercial.

The output circuit current 11 is the DC component bd of the circuit current I.

Electricity equal to flows. The other circuit current I! ′ flows a current equal to the circuit current −1, and its component is also the circuit current 1. Since the DC component bdc and the current transformation component *ao are equal, and the directions of circuit current 1.1 and circuit current 11 are opposite, both currents are subtracted, and the current resulting from the subtraction is applied to the load resistance RLR. If only the AC component of the circuit current 1.1 flows through the load resistor RL, the DC component will be canceled. In general, since the input impedance of the current mirror is low, the AC component b from the circuit current I.
To remove CIO, a large capacitance may be required for capacitor C, 11, but by inserting resistor R, 11, the input impedance of current mirror CM* seen from capacitor C41 can be increased. , it becomes possible to obtain desired AC rejection characteristics with a small capacitance capacitor.

In the fifth embodiment, the power supply voltage used to generate the current used for subtraction and the fc-source voltage that causes the generation of the DC component are configured separately, so the degree of cancellation of the DC component is different from that of both power supply voltages. Although it depends on the accuracy, in this embodiment, the DC component and the current used for subtraction are generated from a common power supply voltage V, so the DC component cancellation effect is not affected by the value.

FIG. 8 shows a seventh embodiment. Generally, an optical coupling device has a characteristic that the transfer efficiency decreases in a region where the input current is small, and the current mirror 2- can perform a predetermined operation only with respect to one current polarity. In this embodiment, in order to improve this, a constant current source CI is set and a constant current IB is set as the circuit current! , and the lost value is supplied to the feedback resistor J/.In, even when the input voltage VXMM is zero or negative, the optical coupling element PC and the current mirror CM,
It is possible to pass current through. As mentioned in the explanation of the second embodiment, the circuit current! , is determined by the input voltage FINI and the feedback resistor Rf, so the output voltage V. Uo
The above constant current 1. except that a constant current (IIC (N times)) is superimposed on is input voltage VX■ to output voltage r. Ti? 2
It does not adversely affect the transmission characteristics. Conversely, it is also possible to use the above characteristics to control the current value supplied from the constant current source CI. When a device (this 1s device configuration is a well-known technology for telemeter devices, etc.) is connected, it can also be applied to control the power supplied to the device.
However, depending on the application, this can be a great advantage.

FIG. 9 shows the eighth embodiment, in which the current coupling part is in a balanced transmission format in order to eliminate the influence of the potential difference r% between the ground air E and G. - As an example, when applied to a feedback circuit This shows the configuration of CM□CMq represents a current mirror, CIDo represents a constant current source, and 200 represents a direct current supplied from the constant current source CID0.

Next, to explain the operation, the current mirror CMa outputs 1
Add terminal and circuit current 1. Outputs the same circuit current 1.1 as , and the direction of the circuit current 1.1 is reversed (from outflow to inflow) by the current mirror CM and becomes I6#, -
Yuashi current source C1ゎ. A direct current IDQ is supplied from the terminal. Therefore, the current mirror CM includes ID0-1. #Circuit current1. III is supplied.

Karen) 12-CM, is the circuit current! , the circuit current 1 from ,
To subtract III, the circuit current 1. ' is reversed to create a circuit current of 1.1111, and the circuit current 1.1111, which is the result of the subtraction, is applied to the feedback resistor R1. '# is supplied. Here, focusing on the DC current ID0 supplied by the constant current source CI9°, by selecting the coefficients of the current mirror CM on a one-to-one basis, the multi-circuit current 1. '# and circuit current 1. The current based on the DC current IDO flowing in # is not strong, and the current based on the DC current ID0 flowing in the circuit current 1.1111 has the same effect as the constant current source CI in the 70th embodiment, and the current based on the DC current ID0 flowing in the circuit current 1. 1. DC current ID flowing through III
The O-based current acts as a bias current for the current it-CMq.

Next, circuit current 1. The circuit current that flows based on! , and 1
．． The operation regarding ' is that the circuit current 1.1 is a current mirror C
The directions of M and CM are reversed twice and added (or subtracted if we focus on the circuit current 1.'), and in the end Karen) (
Two CMs circuit current 16 or! , 2 of the current flowing through '
Double the current will flow through the feedback resistor Rf. Therefore, the relational expression I, MV□1/J/ shown in the second embodiment is (1, +1.') w=21. = V,. /
to Rf, and Iq-1,×N-7(VxN,/Rf)
The operation is similar to that described in detail in the second embodiment, etc., except that the value is changed to xN.

Next ic Considering the current based on the potential difference between E and G, the output impedance of the current structure 2- has a finite value in a practical circuit, and the current value of the current mirror (mirror ratio) changes depending on the potential difference between E and 0. And circuit current! , and 1. ′
include currents of Δ with the same phase, but as already explained, the current mirror CM changes the circuit current 1. and! , # are subtracted, so they do not affect the path from the current mirror CM to the feedback resistor R1, and therefore, according to this embodiment, it is possible to eliminate the influence of the potential difference between E and 0.

FIG. 10 shows a ninth embodiment, in which a specific configuration example of the constant current source CID0 in the eighth embodiment includes a resistor R6 and a current mirror CM, and shows the output of the current t19-cx. This is also intended to cancel out the direct current component contained in the circuit current I. The cancellation operation is performed when the circuit current 1. The DC current component based on the DC current IDO included in ## is the DC current Il.

The current mirror CM is realized by subtracting a current N72 times the DC current IDO from the multi-circuit current I9, and both currents being subtracted are The same current (i.e. vJx according to Fig. 10)
o), so the direct current /D.

A highly accurate cancellation operation independent of the value of is achieved.

The embodiments of the present invention have been described above.

Since there are many cases in which normal information transmission requires bidirectional transmission, in most of the embodiments, signal transmission means in each direction are explained in the same embodiment, but for applications requiring only unidirectional transmission. This is to explain the case where a general current mirror is used as the current generation means, because it is clear that it is possible to eliminate the circuit related to transmission in unnecessary directions. It is true that the transmission characteristics of the coupling part to the side are not affected by the actual characteristics due to feedback, but the transmission ratio between the input and output of the current mirror also affects the overall characteristics. Therefore, it is also possible to eliminate the transistor at the input stage of the current mirror shown in FIG.

As explained above, according to the present invention, it is possible to apply an element with insufficient equality to the coupling part from one side to the other side (in the embodiment, from the low withstand voltage side to the high withstand voltage side). A large degree of freedom is obtained in circuit design, and as shown in the example, the low voltage side and high voltage side can be separated into information input/output pairs, making it easy to integrate circuits, making it more economical, and reducing the chip area. It has the advantage of being able to Furthermore, to describe the features of the present invention corresponding to each embodiment, the first embodiment shows the basic configuration of the present invention, and the second embodiment applies the present invention to bidirectional transmission. In this case, there is an advantage that the circuit configuration can be separated into a low voltage side and a high voltage side, and the fifth embodiment shows that it is possible to apply an optical coupling element to the coupling means. 2- can be applied, the fourth embodiment provides a means of securing against overvoltage on the low withstand voltage side, and the fifth embodiment has the advantage of being able to cancel out the DC component. A] The sixth embodiment has the advantage of being able to eliminate the influence of the power supply voltage when canceling the DC component, and the seventh embodiment can utilize the optimum operating point of the current tunneler, and also has the advantage of being able to eliminate the influence of the power supply voltage when canceling the DC component. The advantage of the embodiment is that it can transmit signals (To), the embodiment of Tate 8 has the advantage of being able to eliminate the influence of the potential difference between the ground air X and O, and the advantage of the ninth embodiment is that it can prevent bias current from appearing in the output. There is.

Having described the above in detail, the features of the embodiments of the present invention are as follows.

1. Apply current coupling to the information coupling means from the other side to the one side provided as necessary. '2 Use an optical coupling element as a means for coupling information from one side to the other.

5- Using a current output element such as a current 2- as a means for coupling information from one side to the other. -4 Must be equipped with means for canceling the DC component.

& The connection from the other side to one side is balanced transmission.

& Be equipped with bias current adding means.

7.1 [Means for generating currents whose numbers are proportional to each other are constructed by a plurality of transistors, whose bases are connected in common to serve as input terminals, and the collectors of each transistor are used as output terminals; After inserting a resistor as necessary on the Z vine side, connect it in common and use it as a common terminal (source side terminal).

[Brief explanation of drawings]

FIG. 1 shows a first embodiment illustrating the principle of the present invention, FIG. 2 and FIGS. 4 to 10 show second to ninth embodiments of the present invention,
FIG. 3 is a rounded diagram explaining the current denominator 2-. Input, C30Os C561"' Output of current generating means,
CUP...coupling means, CUPt-coupling means input,
CUP--Output of coupling means, OPA--Operation amplifier, CM to CM,--Current O2'Ll
, RXJ, R1111, Rf, Rat to J
igs. R41, Ro-resistance, pc-optocoupler layer FIMI,
VXN2 ``'Interface nice circuit input signal,''
01171, VOTJ't2...output signal of the interface circuit, not nos..."diode, LG-earth, Fs"" Potential difference between EtG, Vo, -
rI! ...Power supply voltage, 11 to Ima 1j, 1. Il
, 1. III, 1; III, 1. mll,
... Surrounding current. Patent applicant: 4 people from outside Nippon Telegraph and Telephone Public Corporation Patent attorney Gobe Tamamushi (5 people from outside) Figure 11 Figure 3 (α) (b')
(C) Continuation of Figure 10, page 1 ■Applicant Oki Electric Industry Co., Ltd. 1-7-12 Toranomon, Minato-ku, Tokyo ■Applicant Fujitsu Ltd. 1015 Kamiodanaka, Nakahara-ku, Kawasaki City

Claims (1)

[Claims] In an interface circuit for transmitting information between two points from one side to the other side, a coupling means for transmitting information from the one side to the other side, and a coupling means connected to the output end of the skeleton coupling means. current generating means for generating a plurality of mutually proportional currents, and a feedback output of one of the outputs from the current generating means connected to the input end of the coupling means and an input signal. 1. An interface circuit comprising: control means for comparing the signals, determining a match between the two in a proportional relationship, and controlling the input signal to the coupling means.