JPS6373406A - Ripple filter - Google Patents

Abstract

PURPOSE:To obtain a ripple filter with which the output voltage can be set at a high level by using a lateral PNP transistor TR having the same length between a base-emitter junction and a base-collector junction. CONSTITUTION:A lateral PNP TR contains an N-type epitaxial layer 32 laminated on a P-type semiconductor substrate 31, an N<+> type buried layer 33 which is buried into the surface of the substrate 31, a P<+> separated area 34 which pierces through the layer 32 as if it enclosed the layer 33, an island-shaped area 35 isolated by the area 34, an emitter area 36 formed on the surface of the area 35, a P-type collector area 37 which is formed opposite to and with a distance from the area 36, and a guard ring area 38 which is formed as it is enclosed both areas 36 and 37. Then, an approximately equal length is secured between a base-emitted junction and a base-collector junction. Such lateral PNP TR is used as a current driving TR of a ripple filter of a low saturation type and a differential amplifying type. Thus, it is possible to obtain a ripple filter that can work at a low power supply voltage and can secure a high output voltage level.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a ripple filter for removing ripples contained in a power source, and is particularly suitable for IC (integrated circuit), and has a low power supply voltage. This article relates to a ripple filter that can be operated effectively.

(B) Conventional Technology Ripple filters are used in normal audio equipment to remove power ripples superimposed on power lines and power noise caused by motor rotation. Ripple filters that consist of capacitors and resistors are often used, but for example, large-value capacitors and resistors cannot be used in portable devices that operate on 1.5V or 3V batteries. Therefore, there was a problem that it could not withstand use due to its characteristics.

As a ripple filter that can operate with a low power supply voltage, a low saturation type ripple filter using a transistor as shown in FIG. 6 is described in, for example, Japanese Patent Application No. 115098/1983.

In FIG. 6, the first and second transistors (1) and (2) constitute a differential amplifier circuit (winter), and the first and second transistors (1) and (2) constitute a differential amplifier circuit (winter).
A reference voltage obtained at the midpoint between the first and second voltage dividing resistors (4> and (5)) is applied to the base of the transistor (1), and the output signal of the differential amplifier circuit (3) is Fifth
The current is amplified by the transistors (6) to (8) and can be led out to the output terminal (9). In that case, the output signal obtained at the output terminal (9) can be fed back to the base of the second transistor (2), so that the voltage at the output terminal (9) becomes equal to the reference voltage. The filter effect of the ripple filter shown in FIG. 6 is obtained by the resistor (10) and the capacitor (11), and since the current flowing through the resistor (10) is only the base current of the first transistor (1) and is small, The value of the resistor (10) can be increased.

Therefore, even if the value of the capacitor (11) is made small, a sufficient filter effect can be achieved. Also, the reference voltage applied to the base of the first transistor (1) is . Then, the power loss is Vcc-Vo (Vec is the power supply voltage), but if the value of the second voltage dividing resistor (5) is made sufficiently larger than the value of the first voltage dividing resistor (4), , the power loss can be reduced. However, in that case, the output terminal (9)
Since the output voltage of the fifth transistor (8) is equal to the reference voltage, the value of the reference voltage must be set within a range in which the fifth transistor (8) is not saturated due to power supply ripple.

When converting the ripple filter as described above into an IC,
The fifth transistor (8) is a lateral PN with the following structure.
It is conceivable to use a P transistor.

FIGS. 7A and 7B show a general lateral PNP transistor, which includes an N-type epitaxial layer (22) stacked on a P-type semiconductor substrate (21), and a substrate (21).
An N+ type buried layer (23) formed by being buried in the surface, and an epitaxial layer surrounding the buried layer (23)! (2
2), an island region (25) formed in an island shape by the isolation region (24), and a P-type emitter region (26) formed on the surface of the island region (25).
), a P-type collector region (27) formed apart from each other so as to surround this emitter region (26), and an N3-type base contact region (28).

(c) Problems to be solved by the invention However, the conventional lateral PNP transistor has only one
Since the rise characteristic of c is poor and the saturation voltage is large, there is a drawback that the output voltage cannot be set high enough in consideration of the ripple removal rate. When the fifth transistor (8) is operating normally without being saturated, a good ripple removal rate can be obtained even if the output voltage is set relatively high as shown in FIG. 8A.

However, when the power supply ripple becomes large and the fifth transistor (8) becomes saturated at the peak of the lower waveform, the ripple removal rate deteriorates rapidly as shown in FIG. 8B. Further, when the load resistance becomes small and the output current increases, the saturation voltage of the fifth transistor (8) becomes large, and the ripple removal rate deteriorates as shown in FIG. 8C.

In order to prevent this deterioration of the ripple rejection rate, it is possible to lower the reference voltage and keep the output voltage low, but in equipment that uses a low power supply voltage, it is necessary to This is not desirable as it will cause deterioration.

(d) Means for Solving the Problems The present invention has been made in view of the above-mentioned drawbacks, and includes a P-type emitter region formed on the surface of one island region (35) as a base in the fifth transistor (8). (36) and a P-type collector region (37) formed in a spaced apart manner so as to face this emitter region (36). By using lateral PNP transistors of equal length, the output voltage can be set sufficiently high, providing a ripple filter suitable for use in equipment that uses a low power supply voltage.

(e) Effect When a PNP transistor operates, holes are injected from the emitter to the base and holes are injected back from the collector to the base at the same time, and the difference in the amount of holes injected between the two is the collector current. become.

When a sufficient potential difference is applied between the collector and emitter and the base-collector junction is in a reverse bias state, the amount of holes reversely injected from the collector to the base is extremely small compared to the amount of holes injected from the emitter to the base. Therefore,
A large flef electric current method. f! : Can flow. Furthermore, in this state, the amount of electrons back-injected from the base to the collector is extremely small, so the base current is also small, and the transistor can operate in a high h□ state.

However, if the potential difference between the collector and emitter is not sufficient and the potential of the collector rises relatively, causing the base-collector junction to become forward biased, the amount of holes injected from the collector to the base will be smaller than the amount of holes injected from the emitter to the base. Because the amount of holes reversely injected increases rapidly, the Fref current method is used. is drastically reduced.

In the conventional lateral PNP transistor shown in FIG. 7, since the emitter region (26) is surrounded by the collector region (27), the efficiency of capturing minority carriers (holes) injected from the emitter region (26) is excellent. If the base-collector junction is sufficiently reverse biased, it will exhibit a high h□.
As mentioned above, in a situation where the base-collector junction is forward biased, the reverse injection efficiency of holes from the collector to the base is superior to the efficiency of hole injection from the emitter to the base, so the IC's rise characteristics are Unfortunately, the VC,(sat) at that time becomes large.

On the other hand, the lateral PN used in the present invention of the first vgJ
In the P transistor, the junction lengths of the base-emick junction and the base-collector junction are made to be approximately the same length, so while maintaining a certain level of height and □ in the active region, there is a region where the base-collector junction becomes forward biased. In this case, the efficiency of hole injection from the emitter to the base and the efficiency of hole injection from the collector to the base are approximately equal, so that V is lower than that of the conventional method. Collector current I from emitter to collector even in the region where t is significantly reduced. Therefore, the saturation voltage VC,(sat) can be made considerably smaller.

Therefore, according to the present invention, a lateral PNP as described above
Since a transistor is used as the output transistor, the ripple rejection rate can be improved and the output voltage can be set sufficiently high.

(f) Example Hereinafter, the ripple filter of the present invention will be explained in detail with reference to the drawings. In FIG. 2, the first and second transistors (1) and (2) constitute a differential amplifier circuit (base), and the base of the first transistor (1) has a first
The obtained reference voltage is applied to the connection midpoint of the second voltage dividing resistors (4) and (5), and the output signal of the differential amplifier circuit (Dan) is applied to the third to fifth transistors (6) to (8). ), the current is amplified and output to the output terminal (9). In that case,
The output signal obtained at the output terminal (9) can be fed back to the base of the second transistor (2).
The voltage 9) becomes equal to the reference voltage. The filter effect of the ripple filter shown in FIG. 2 is obtained by the resistor (10) and the capacitor (11), and since the current flowing through the resistor (10) is only the base current of the first transistor (1) and is small, The value of the resistance (0) can be increased.

Therefore, even if the value of the capacitor (11) is made small, a sufficient filter effect can be achieved.

Now, the source voltage VCC is high enough for the fifth transistor (8)
In a normal state where the voltage is not saturated, the output voltage obtained at the output terminal (9) becomes equal to the reference voltage obtained at the connection midpoint of the first and second voltage dividing resistors (4) and (5) due to negative feedback. In addition, since the reference voltage is the voltage after the power supply ripple has been removed by the capacitor (11), the output voltage can be kept constant. At this time, the power supply ripple applied to the emitter of the fifth transistor (8) is absorbed by changing the collector-emitter voltage of the fifth transistor (8).

However, when the power supply ripple becomes large and the power supply voltage VCC momentarily drops, the vc! of the fifth transistor (8)!
is extremely low. is drastically reduced, and it becomes impossible to draw in the collector current corresponding to the base current, which is the output signal of the differential amplifier circuit (multiple). Then, the change in power supply ripple is expressed as ■ of the fifth transistor (8). 4, the output voltage is reduced by the amount of the power supply ripple and the saturation voltage at that time, resulting in a worsening of the ripple removal rate. Furthermore, when the output current increases due to load fluctuations, the saturation voltage of the fifth transistor (8) increases, which tends to cause similar results.

Therefore, as the fifth transistor (8), even if the saturation voltage is as small as possible, even in a region where vo east is extremely low, sufficient h
F! A transistor that maintains this is desired.

A feature of the present invention is that a lateral PNP transistor as described below is used for the fifth transistor (8>) as described above.

FIG. 1A and FIG. 1B are cross-sectional views showing such a lateral PNP transistor. An N+ type buried layer (33) buried in the surface and an epitaxial layer (32) surrounding the buried layer (33).
) and a P1-type separation region (34) penetrating through the separation region (
34), and a P-type emitter region (35) formed on the surface of the island region (35).
6), a P-type collector region (37) formed opposite to and spaced apart from the emitter region (36), and an emitter region (36).
36) and an N" type guard ring region (38) formed so as to surround the collector region (37),
The junction lengths of the base-emitter junction and the base-collector junction, which are active as a transistor, are made approximately equal.

The guard ring area (38) is the base island area (35).
> is shared as a contact for the emitter region (36)
It is also formed into a ring shape to prevent leakage current from the collector region (37) to the isolation region (34). At this time, the high concentration guard ring region (38) comes into contact with each region, which deteriorates the withstand voltage, but there is no problem if it is used at a low power supply voltage as in the present invention. In addition, in this embodiment, in order to almost completely prevent leakage current to the isolation region (34), a guard ring region (38) is formed with a diffusion region reaching from the surface of the island region (35) to the buried layer (33). However,
Shallower than this, for example, the collector contact region in Figure 7 (
It is also possible to form a diffusion region similar to 28).

The lateral PNP transistor formed in this way has a shorter junction length of the base-collector junction with respect to the base-emitter junction than the conventional one, and therefore
When the collector junction becomes forward biased, the efficiency of reverse injection of holes from the collector to the base is low. Therefore, even if the same forward bias is applied, the amount of reverse injection of holes from the collector to the base is smaller than the amount of holes injected from the emitter to the base in the case of the present invention, so the collector current I caused by the difference between them is smaller. . It is possible to allow a larger amount of to flow, and the saturation voltage Vat (Sat) can be relatively lowered. It is conceivable to take this one step further and shorten the collector-base junction length with respect to the emitter-base junction, but this would be difficult to achieve in the active region.

This is not preferable because it will not be possible to remove it.

3A and 3B show the transistor characteristics of the inventive transistor shown in FIG. 1 and the conventional transistor shown in FIG. 7, respectively. As is clear from the figure, the present invention does not require much effort. Because of its excellent rise characteristics, when 1b = 1 [μA], the conventional type
When e=50 (mV), hFI!=10, whereas in the case of the present invention, when Ib=1 [μA], Vct=35 CmV) already exceeds bvw=10. Mote vc! In the saturated region where the
In addition, since the leakage current due to the parasitic PNP transistor with the substrate (31) cannot be ignored, current apparently flows in the opposite direction from the emitter to the collector.

Now, in the circuit diagram shown in Figure 2, when the reference voltage is set to a sufficiently high value < 0.90V at vcc = 1.5V, and when VCC drops to 1.0■, a power supply ripple with a maximum amplitude of -0.04V will occur. Assuming that these are superimposed, the remaining voltage of 0.06V L will not be applied to v4 of the fifth transistor (8). VC! Comparing Figures 3A and 3B at = 0.06V, the conventional one is completely in the saturation region, while the one of the present invention still maintains a certain degree of h□. I can see that it is. If the fifth transistor (8) maintains a certain level of ht, this ripple filter can maintain its function of removing power supply ripple.

Therefore, according to the present invention, it is possible to provide a ripple filter that has an excellent ripple removal rate due to the reduced saturation voltage and can thereby set the output voltage sufficiently high.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention.
1) is a differential amplifier circuit having first and second transistors (42) and (43) whose emitters are commonly connected;
4) connects the reference voltage obtained at the midpoint between the first and second voltage dividing resistors (45) and (46) to the first transistor (4).
(47) is a first current inversion circuit that inverts the collector current of the first transistor (42); (48) is a bias circuit that applies the voltage to the base of the second transistor (42);
a second current inversion circuit for inverting the collector current of (3);
9) is a third current inverting circuit that further inverts the output current of the first current inverting circuit (lamp), (50) to (52) are the second and third current inverting circuits (average) and (4th grade). Third to fifth transistors for amplifying the difference current; (53) is a detection transistor for saturation detection whose emitter is connected to the collector of the third transistor (50) and whose base is connected to the collector of the fourth transistor (51); , and (54) are control transistors that can be controlled by the output signal of the detection transistor (53). Note that (55) is an output terminal, (
56) is a capacitor for ripple removal.

The second embodiment of the present invention is characterized by providing a detection circuit for detecting that the output transistor is saturated, and means for lowering the reference WEE in accordance with the output signal of the detection circuit.

In the normal operating state where the fifth transistor (52) is not saturated, the hyt (current amplification factor) of the fifth transistor (52) is high, so its base current is small and the base voltage of the detection transistor (53) is kept high. dripping Also,
Since the collector voltage of the third transistor (50) is low, the emitter voltage of the detection transistor (51) is also kept low. Therefore, the detection transistor (53) is never turned on, and the control transistor (54) is also never turned on.

When the power supply ripple becomes large or the output current becomes large, the fifth transistor (52) becomes saturated and h□ decreases, the base current of the fifth transistor (52) becomes excessive, and the third and fourth transistors (50) and <51) are also saturated. Therefore, the base voltage of the detection transistor (53) drops to near ground, and the detection transistor (53)
) rises to near the power supply voltage. As a result, the detection transistor (53) is turned on, the control transistor (54) is turned on, and the first transistor (52) is turned on.
lowers the base voltage, i.e., the reference voltage. When the reference voltage decreases, the output voltage available at the output terminal (55) also decreases, thereby causing the fifth transistor (52) to
is released from saturation, so deterioration of the ripple removal rate can be prevented.

As the fifth transistor (52), the lateral PN shown in FIGS. 1A and 1B is used as a feature of the present invention.
A P transistor is used. According to this embodiment, the fifth
Even if the transistor (52) is saturated, the circuit is configured to release it, so the ripple rejection rate is excellent under normal conditions, and it is possible to prevent deterioration of the ripple rejection rate even when there is excessive ripple or when the load current increases. Therefore, the output voltage during normal operation can be set to the maximum, and since the saturation voltage of the fifth transistor (52) is small, the output voltage can be set even higher. Moreover, according to this embodiment, since the ripple removal rate is excellent, for example, V. It can also be very easily incorporated into an IC that compensates for voltage reduction characteristics up to 1.0■ at c=t and 5V.

FIG. 5A and FIG. 5B are a sectional view and a plan view, respectively, for explaining the third embodiment of the present invention. The epitaxial layer (32), the N''-type buried M<33> formed in the surface of the substrate (31), and the epitaxial layer (32) are penetrated so as to surround this buried layer (33). P1
A mold isolation region (34), an island region (35) formed into an island shape by the isolation region (34), and P-type emitter regions (36) arranged alternately at a distance on the surface of the island region (35). and collector regions (37), and these emitter regions (3
6) and a guard ring region (38) formed to collectively surround the collector region (37), and emitter regions (36) are provided at both ends. Emitter area (3
6) and the collector region (37) are formed to have the same shape and size, and the distance between them (base width) is also exactly the same. Lateral PNPs formed in this way
! -A transistor is a transistor with an active base.
Although the emitter junction and the base-collector junction have approximately the same junction length, since the emitter regions (36) are placed at both ends, holes are injected from the emitter to the base which cannot be prevented by the guard ring region (38). This is equivalent to increasing the base-emitter junction length. Therefore, the saturation voltage in the low voltage region is lower than that of the lateral PNP transistor shown in FIG.

If the above-mentioned transistor is used as the output transistor, it is possible to construct a ripple filter whose characteristics are further improved by the first and second embodiments.

(G) As described in detail, the present invention provides a ripple filter that has an excellent ripple removal rate during normal operation, has little deterioration of the ripple removal rate even when the voltage is reduced, and can set the output voltage sufficiently high. It has the advantage of being able to provide In addition, since the output voltage can be set sufficiently high, the output voltage can be reduced. Excellent pressure characteristics, 1.5■
Ya 3. It has the advantage that it can be used in equipment that uses a low power supply voltage of Ov to provide a suitable ripple filter. According to the second embodiment of the present invention, there is an advantage that the ripple rejection rate does not deteriorate even when the ripple is excessive or when the load current increases, and a ripple filter can be provided in which the -i output voltage is set higher. According to the present invention, no additional steps are required to construct the lateral PNP transistors shown in FIGS. Especially in terms of Ic max, even when an external transistor is connected in parallel to the fifth transistor (8), there is an advantage that a ripple filter with good characteristics can be constructed.

[Brief explanation of the drawing]

FIG. 1A and FIG. 1B show the lateral P used in the present invention, respectively.
2 is a circuit diagram showing a ripple filter of the present invention, and FIGS. 3A and 3B are diagrams of a lateral PNP transistor used in the present invention and a conventional lateral PNP transistor, respectively. A transistor characteristic diagram, FIG. 4 is a circuit diagram showing a second embodiment of the present invention, and FIGS. 5A and 5B are a plan view and a sectional view, respectively, for explaining a third embodiment of the present invention. , FIG. 6 is a circuit diagram for explaining a conventional ripple filter, FIGS. 7A and 7B are a plan view and a cross-sectional view of a conventional lateral PNP transistor, and FIGS. 8A to C are ripple removal rates. FIG. (base) is a differential amplifier circuit, (4) and (5) are voltage dividing resistors, (
8) is a fifth (output) transistor, (31) is a P-type semiconductor substrate, (36) is an emitter region, (37) is a collector region, and (39) is a guard ring region. Applicant Sanyo Electric Co., Ltd. and one other agent Patent attorney Takuji Nishino and one other person Figure 1 8 Figure 2 VCC Figure 3 △ Figure 3 B 5 U) To Figure 5 Figure 5 B Figure 6 + Vcc Figure 7△ Figure 7B Figure 8A Time (1)

Claims (1)

[Claims] (1) A differential amplifier circuit including first and second transistors whose emitters are commonly connected, means for supplying a reference voltage to the base of the first transistor, and current amplification of the output signal of the differential amplifier circuit. an output transistor;
A ripple filter is provided with a ripple removal capacitor connected to the base of the transistor, and the output signal of the output transistor is fed back to the base of the second transistor. A base-emitter junction and a base-collector junction active as a transistor, comprising an emitter region of one conductivity type formed on the surface and a collector region of one conductivity type formed apart from and opposite to the emitter region. A ripple filter characterized by using lateral transistors having substantially equal lengths.