JPH0622999Y2 - Pair Zener diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a pair Zener diode having symmetrical voltage / current characteristics in both forward and reverse directions, which is used in a mV isolator and the like, and in particular, its pair matching characteristic is improved. Regarding a pair Zener diode.

<Prior Art> There is a circuit shown in FIG. 6 as a pair diode serving as an improved base used for this type of isolator.
This pair diode will be described.

Reference numerals 11 and 12 are input terminals to which a DC voltage signal Ei is applied, C ₁ is a capacitor connected between the input terminals 11 and 12, D ₁₁ and D ₁₂ are diodes connected in parallel with opposite polarities, and TR is a primary winding. The transformer has n ₁ , a secondary winding n ₂ , and a tertiary winding n ₃ . D ₂₁ and D ₂₂ are diodes connected in parallel in opposite polarities to each other, 21 and 22 are output terminals, and C ₂ is a capacitor connected between the output terminals 21 and 22, and these capacitors constitute signal averaging means. The primary winding n ₁ of the transformer TR is connected to the input terminals 11 and 12 via the parallel diode circuit D ₁ and these constitute an input circuit. Further, the secondary winding n ₂ is connected to the output terminals 21 and 22 through the parallel diode circuit D ₂ , and these and the capacitor C ₂ form an output circuit.

The circuit shown in FIG. 6 has a circuit configuration in which the primary side and the secondary side are symmetrical with respect to the transformer TR.
A pulse generator OS is connected to the tertiary winding n ₃ .

FIG. 7 is a characteristic diagram of the parallel diode circuits D ₁ and D ₂ , and the applied voltage e ₁ and the flowing current i ₁ have a non-linear relationship as shown.

In the isolator having such a configuration, the turns ratio of the primary winding n ₁ and the secondary winding n ₂ of the transformer TR is set to 1: 1.
Assuming that a positive and negative symmetrical impulsive signal is given to the tertiary winding n ₃ , its equivalent circuit is as shown in FIG.

In the equivalent circuit shown in FIG. 8, the switches S ₁ and S ₂ represent switching operations of the diodes D ₁₁ , D ₁₂ , D ₂₁ and D ₂₂ , and a positive impulse is applied from the pulse generator OS. Then switch S ₁ ,
S ₂ is connected to the contact a side (diodes D ₁₁ , D ₂₁
When the negative polarity impulse is applied, the switches S ₁ and S ₂ are connected to the contact c side (diode D).
₁₂ and D ₂₂ are conductive). Further, in a state in which the impulse is not applied, the switches S ₁ and S ₂ are connected to the contact b (none of the diodes is conductive). Each diode D ₁₁
Each of D ₂₂ to D ₂₂ is represented by a series connection of a forward voltage Δ and a dynamic resistance (forward resistance) r.

Now, in the state in which the positive polarity impulse i _o is applied from the pulse generator OS, the switches S ₁ and S ₂ are connected to the contact a.
It is equivalent to being connected to (the diodes D ₁₁ and D ₂₁ are conducting), and the impulse i _o is equally shunted to the diode D ₁₁ side and the diode D ₂₁ side by i _o / 2 as shown in the figure. In this state, the output voltage E _o1 between the output terminals 21 and 22 can be expressed by the equation (1).

E _o1 = E _i + Δ ₁₁ + i _o (r ₁₁ −r ₂₁ ) −Δ ₂₁ (1) Further, in the state in which the negative polarity impulse i _o (the amplitude is the same as that of the positive polarity) is applied, Output terminals 21, 2
The output voltage E _o2 between the two can be expressed by equation (2).

E _o2 = E _i −Δ ₁₂ + i _o (r ₁₂ −r ₂₂ ) + Δ ₂₂ (1) The positive and negative polarity impulse from the pulse generator OS is the ninth pulse.
As shown in FIG. 9 (a), when the voltage is applied in a repeating cycle T, and the capacitances of the capacitors C ₁ and C ₂ are set sufficiently large so that the potential change due to the charge / discharge of the impulse becomes small, the output voltage E _o is the average value of E ₀₂ ,
It can be expressed by equation (3) from equation (1) and equation (2).

E _o = (E _o1 + E _o2 ) / 2 = E _i + (Δ ₁₁ −Δ ₁₂ −Δ ₂₁ + Δ ₂₂ ) / 2 + i _o (r ₁₁ −r ₁₂ −r ₂₁ + y ₂₂ ) / 4 (3) (3) ), If Δ ₁₁ = Δ ₁₂ , Δ ₂₁ = Δ ₂₂ r ₁₁ = r ₁₂ , r ₂₁ = r ₂₂ (4), the second and third items are both zero, and the output voltage is zero. E _o becomes equal to the input DC voltage E _i . Therefore, the DC voltage given to the input circuit can be electrically insulated and taken out from the output circuit side.

In such a small signal isolator, whether or not the parallel diode circuits D ₁ and D ₂ satisfy the relationship of the expression (4) is an important factor that determines the accuracy of the isolator.

Therefore, as disclosed in Japanese Examined Patent Publication No. 59-12018, four diodes are formed close to each other on a substrate and first and second terminals are provided.
One pair of diodes located diagonally between the terminals of is connected in parallel in the direction from the first terminal to the second terminal, and the other pair of diodes located diagonally to each other is connected to the second pair of diodes. The accuracy is improved by connecting in parallel so that the direction from the terminal to the first terminal is the forward direction.

<Problems to be solved by the invention> However, when such a conventional pair diode is used for an isolator, it is smaller than the rising voltage of the diodes of the parallel diode circuits D ₁ and D ₂ (about 0.6 V in the case of a silicon diode). The DC voltage E _i can be isolated, but when a DC voltage E _i larger than this is input, a current flows from the external circuit to the isolator circuit, and thus there is a problem that it does not function as an isolator circuit.

<Means for Solving the Problems> In order to solve the above problems, the present invention is configured so that four diodes formed on a substrate and having the same voltage / current characteristics are arranged close to each other so as to be center-symmetrical. And a first and a second terminal are provided between the first and second terminals, and a line connecting the first and second terminals of the two sets of the diodes diagonally located as a first series circuit. Each set of diodes arranged on one side is serially wired in the opposite direction to each other, and each set of diodes arranged on the other side is connected so that the connection is the same as the first series circuit as the second series circuit. The wires are connected in series in directions opposite to each other and are connected in parallel to the first series circuit, and the series wires are arranged symmetrically with respect to the first and second terminals so that voltage / current characteristics in both forward and reverse directions can be obtained. Symmetric .

<Operation> The first series circuit has a configuration in which the diode and the Zener diode are connected in series because the pair of diodes are connected in opposite directions, and the second series circuit is also the same circuit as the first series circuit. It is composed. However, since the diodes and zener diodes of each series circuit are arranged symmetrically with each other, the forward voltage drop, zener voltage, etc. are similarly affected by the ambient temperature gradient, etc., and the matching property is improved as a whole. In addition, isolation with excellent temperature characteristics can be achieved even with a high input DC voltage.

<Embodiment> An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of one embodiment of the present invention, and FIG. 2 is a partial sectional view of the embodiment shown in FIG.

30 is a P-type and a silicon substrate. Rectangular regions 31, 32, 33, and 34 forming four n-type transistors are formed on this so as to be center-symmetric with respect to the midpoint A. FIG. 2 shows a partial cross section showing a cross section cut at the central portion BB ′ of the rectangular region 31 among these. Since each of the rectangular areas 32, 33, and 34 has the same configuration as the rectangular area 31, the rectangular area 31 will be mainly described.

In the center of the rectangular region 31, a rectangular n ⁺ -type emitter 31 is formed.
E has a rectangular p-shaped base 31B around its outer periphery,
Further, rectangular n ^{+ -type} collectors 31C are formed around the outer periphery thereof (FIG. 2) to form a transistor 31T.

The other rectangular regions 32, 33, and 34 have the same configuration as the transistor 31T and have the same structure as the transistor 32T (emitter 3).
2E, base 32B, collector 32C), 33T (emitter 33E, base 33B, collector 33C) and 4
3T (emitter 34E, base 34B, collector 34
C) is formed.

On the collector 31C and the base 31B of the transistor 31T, an aluminum wiring 31A for connection shown by diagonal lines is formed (however, omitted in FIG. 2) and diode-connected to form a diode 31D.

Similarly, for the other transistors 32T, 33T and 34T, aluminum wirings 32A, 33A and 34, respectively, are similarly provided.
Wired at A.

The emitter 31E of the transistor 31T and the emitter 32E of the transistor 32T are connected by an aluminum wiring 35, and the emitter 33E of the transistor 33T and the emitter 34E of the transistor 34T are connected by an aluminum wiring 36, respectively.

Further, the terminal 37 is wired at an equal distance to the collector 32C of the transistor 32T and the collector 34C of the transistor 34T by the aluminum wirings 39 and 40 via the aluminum wiring 38 and the middle point A.

The terminal 41 is connected to the aluminum wirings 43 and 4 via the aluminum wiring 42.
4 by the collector 31C of the transistor 31T
And the collector 33C of the transistor 33T are wired at an equal distance. The upper and lower aluminum wirings are formed symmetrically with respect to the line connecting these terminals 37 and 41.

FIG. 3 shows each transistor 31T formed in this way,
The state of connection of 32T, 3T, and 34T is shown in an equivalent circuit together with the chip layout for easy understanding.

Next, the operation of the embodiment shown in FIG. 1 configured as described above will be described with reference to FIGS. 4 and 5.

FIG. 4A shows the function of each element when the current I flows from the terminals 41 to 37, and FIG. 4B shows the function of each element when the current I flows from the terminals 37 to 41. Shows.

Each of the diodes 31D to 34D functions as a forward diode when the current I flows in the forward direction, and the current I flows in the reverse direction.
When it flows, it functions as a Zener diode. Therefore, in the case of FIG. 4 (a) in which the current I flows from the terminal 41 to the terminal 37, the diodes 31D and 33D function as forward diodes, and the diodes 32D and 34D function as zener diodes.

As a result, the dead band of the series circuit 45 of the diode 33D and the diode 34D and the series circuit 46 of the diode 31D and the diode 32D is expanded up to the Zener voltage Vz with respect to the positive flow of the current I as shown in FIG. It

On the other hand, the current I from the terminal 37 to the terminal 41
In the case of Fig. 4 (b) where the current flows, diodes 31D and 33
D is a Zener diode, and diodes 32D and 34
D functions as a forward diode. As a result, the dead band of the series circuit 47 of the diode 33D and the diode 34D and the series circuit 48 of the diode 31D and the diode 32D expands to the Zener voltage -Vz with respect to the negative flow of the current I as shown in FIG. To be done.

Therefore, the dead zone is expanded to ± Vz for both positive and negative flows of the current I, and the isolation range can be expanded.

Further, by making the diodes 31D to 34D under the same condition, it is assumed that there is a temperature gradient from the series circuit 45 (47) side to the series circuit 46 (48) side with respect to the line connecting the terminals 41 and 37. Also, since the diodes constituting each series circuit always include the diodes on the upstream side and the downstream side of the temperature gradient, and these series circuits are connected in parallel, the influence of temperature is averaged and the influence thereof is And 3
It does not appear between 7.

This relationship is the same when a temperature gradient is generated from the terminal 41 side toward the terminal 37 side.

In this configuration, the diode included in each series circuit functions as a temperature compensating element for the Zener diode and is useful for improving the temperature characteristic.

Further, in the above case, the diode-connected transistor is formed on the substrate, but the present invention is not limited to this, and a pair of diodes and a pair of Zener diodes are closely formed on the substrate and characteristics of breakdown voltage Vz and rising voltage V _BE. May be configured to match.

This pair Zener diode can be applied not only to an isolator but also to a precise protection circuit for positive and negative voltage sources.

<Effects of Device> As described above in detail with reference to the embodiments, according to the present invention, a pair of diodes and a pair of Zener diodes are symmetrically arranged in a cross arrangement and two from each pair. Each series circuit was taken out and connected in series to form each series circuit, and these were connected in parallel symmetrically, so even if there is a temperature gradient on the substrate, it is not affected, and each series circuit always includes a Zener diode. Since the configuration is employed, a paired Zener diode capable of performing temperature-compensated isolation up to a voltage higher than the rising voltage of the diode can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing the construction of one embodiment of the present invention, FIG. 2 is a partial sectional view of the embodiment shown in FIG. 1, and FIG. 3 is a circuit connection of the embodiment shown in FIG. Equivalent circuit, FIG. 4 shows the first
FIG. 5 is a circuit diagram for explaining the operation of the embodiment shown in FIG.
FIG. 6 is a characteristic diagram for explaining the operation of the circuit shown in FIG. 6, FIG. 6 is a circuit diagram showing a configuration of a conventional isolator, FIG. 7 is a characteristic diagram showing a configuration of a parallel diode, and FIG. 8 is a circuit diagram of the circuit shown in FIG. An equivalent circuit diagram and FIG. 9 are explanatory diagrams of the operation. 30 ... Substrate, 31-34 ... Rectangular area, 31T-34T ...
Transistors, 35, 36, 38, 39, 40, 42,
43, 44 ... Aluminum wiring, 37, 41 ... Terminals, 45-4
8 ... Series circuit

Claims (1)

[Scope of utility model registration request] 1. A diode which is formed on a substrate and has the same voltage / current characteristics is arranged in proximity to each other so as to be center-symmetrical, and first and second terminals are provided. Of the two sets of diodes located diagonally to each other as a first series circuit between the terminals, each set of diodes arranged on one side with respect to the line connecting the first and second terminals is connected in series in opposite directions. Wiring, and further, as a second series circuit, each pair of diodes arranged on the other side so as to have the same connection as the first series circuit are serially wired in opposite directions and connected in parallel to the first series circuit. A pair Zener diode is characterized in that the series wirings are arranged symmetrically with respect to the first and second terminals so that the voltage / current characteristics in both forward and reverse directions are symmetrical.