JPH083763B2 - Ripple filter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ripple filter for removing a ripple included in a power supply, and is particularly suitable for an IC (integrated circuit) and operates at a low power supply voltage. Ripple filter that can be made.

(B) Conventional technology In order to remove power supply ripples superimposed on a power supply line and power supply noise caused by rotation of a motor, a ripple filter is used in ordinary audio equipment. As a ripple filter, one consisting of a capacitor and a resistor is often used.For example, in a small portable device that operates on a battery of 1.5V or 3V, it is not possible to use a large value of the capacitor and the resistor. There was a problem that it could not be used.

As a ripple filter that can operate at low power supply voltage,
As shown in FIG. 6, a low saturation type using a transistor is described in, for example, Japanese Patent Application No. 61-115098. In FIG. 6, the first and second transistors (1) and (2)
Constitute a differential amplifier circuit ( 3 ), and the base of the first transistor (1) has first and second voltage dividing resistors (4).
And the reference voltage obtained at the connection midpoint of (5) is applied,
The output signal of the differential amplifier circuit ( 3 ) is current-amplified by the third to fifth transistors (6) to (8) and led to the output terminal (9). In that case, the output signal obtained at the output terminal (9) is 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 of FIG. 6 is obtained by the resistor (10) and the capacitor (11), and the current flowing through the resistor (10) is small only by the base current of the first transistor (1). Said resistance (10)
The value of can be increased. Therefore, the capacitor (1
Even if the value of 1) is small, a sufficient filter effect can be obtained. Further, if the reference voltage applied to the base of the first transistor (1) is V ₀ , the power loss is V _CC −V ₀
(However, V _CC 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. it can. However, in that case, since the output voltage of the output terminal (9) becomes equal to the reference voltage, the value of the reference voltage is the fifth transistor (8).
Must be set within the range that does not saturate due to power supply ripple.

And when integrating the ripple filter as described above into an IC,
The fifth transistor (8) has a lateral PNP with the following structure.
It is conceivable to use a transistor.

7A and 7B show a general lateral PNP transistor, which is formed by laminating an N-type epitaxial layer (22) on a P-type semiconductor substrate (21) and embedded in the surface of the substrate (21). The N ⁺ -type buried layer (23) formed in step 1, the P ⁺ -type isolation region (24) penetrating the epitaxial layer (22) so as to surround the buried layer (23), and the isolation region (24 The island region (25) formed in the shape of an island, the P-type emitter region (26) formed on the surface of the island region (25), and the P-type emitter region (26) formed so as to be spaced apart from each other. The collector region (27) and the N ⁺ -type base contact region (28).

(C) Problems to be solved by the invention However, the conventional lateral PNP transistor has an I _C
Since the rising characteristic is poor and the saturation voltage is large, there is a drawback that the output voltage cannot be set sufficiently high considering 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, if the power supply ripple becomes large and the fifth transistor (8) is saturated at the peak of the lower waveform,
As shown in FIG. B, the ripple removal rate sharply deteriorates. If 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 ripple removal rate, it is sufficient to lower the reference voltage and keep the output voltage low, but in equipment that uses low power supply voltage, the voltage reduction characteristics of the circuit connected to the output terminal deteriorates. It is not preferable because it causes

(D) Means for Solving the Problems The present invention has been made in view of the above drawbacks, and a fifth transistor (8) has a P-type emitter region formed on its surface with one island region (35) as a base. (36) and a P-type collector region (37) formed so as to be opposed to the emitter region (36) so as to be opposed to each other, and a base-emitter junction and a base-collector junction which are active as a transistor are substantially omitted. The output voltage can be set sufficiently high by using the lateral PNP transistors having the same length, and the ripple filter suitable for the device using the low power supply voltage is provided.

(E) Action When the PNP transistor operates, holes are injected from the emitter to the base and back holes from the collector to the base at the same time in the transistor. It becomes an electric current.

Here, when a sufficient potential difference is applied between the collector and the emitter and the base-collector junction is reverse biased, the reverse injection amount of holes from the collector to the base is extremely smaller than the injection amount of holes from the emitter to the base. Since it is small, a large collector current I _C can be passed. Also,
In this state, the amount of back-injection of electrons from the base to the collector is extremely small, therefore the base current is small and the transistor can operate in a high h _FE state.

However, if the potential difference between the collector and the emitter is not sufficient and the potential of the collector rises relatively and the base-collector junction becomes forward biased, the amount of holes injected from the emitter to the base is increased from the collector to the base. Since the reverse injection amount of holes increases rapidly, the collector current I _C decreases sharply.

In the conventional lateral PNP transistor of FIG. 7, since the periphery of the emitter region (26) is surrounded by the collector region (27), the minority carriers (holes) injected from the emitter region (26) are excellent in trapping efficiency, If the base-collector junction is sufficiently reverse-biased, it exhibits high h _FE , but in the situation where the base-collector junction is forward-biased as described above, the efficiency of hole injection from the emitter to the base is higher than the efficiency of hole injection from the collector to the base. Since the reverse injection efficiency of the hole of the above becomes superior, the rise characteristic of I _C is poor, and V _CE (s
at) becomes large.

On the other hand, in the lateral PNP transistor used in the present invention shown in FIG. 1, the junction lengths of the base-emitter junction and the base-collector junction are set to be substantially equal to each other, so that a certain high h _FE is maintained in the active region. , In the region where the base-collector junction is forward biased, the efficiency of hole injection from the emitter to the base is approximately equal to the efficiency of hole injection from the collector to the base.
_{Since the} collector current I _C can flow from the emitter to the collector even in the region where _CE is considerably lowered, the saturation voltage V _CE (sat) can be made considerably small.

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

(F) Embodiment Hereinafter, the ripple filter of the present invention will be described in detail with reference to the drawings. In FIG. 2, the first and second transistors (1) and (2) form a differential amplifier circuit ( 3 ), and the base of the first transistor (1) has a first and a second voltage divider. A reference voltage obtained at the connection midpoint of the resistors (4) and (5) is applied, and the output signal of the differential amplifier circuit ( 3 ) is current-amplified by the third to fifth transistors (6) to (8). To the output terminal (9). In that case, the output signal obtained at the output terminal (9) is 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 of FIG. 2 is obtained by the resistor (10) and the capacitor (11), and the current flowing through the resistor (10) is only the base current of the first transistor (1), so that The value of the resistor (10) can be increased.
Therefore, even if the value of the capacitor (11) is small, a sufficient filter effect can be obtained.

Now, the power supply voltage V _CC is sufficiently high and the fifth transistor (8)
In a normal state in which 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) by negative feedback. Moreover, since the reference voltage is a voltage after the power supply ripple is 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
The collector-emitter voltage of the transistor (8) changes and is absorbed.

However, when the power supply ripple becomes large and the power supply voltage V _CC drops momentarily, V _{CE of} the fifth transistor (8) drops drastically and h _FE drastically decreases, and the output of the differential amplifier circuit ( 3 ) It becomes impossible to draw the collector current corresponding to the base current which is a signal. Then, the change in the power supply ripple cannot be completely absorbed by the change in V _CE of the fifth transistor (8), and the output voltage is reduced by the power supply ripple and the saturation voltage at that time, so the ripple removal rate is deteriorated. It does. Further, when the output current increases due to the change of the load, the saturation voltage of the fifth transistor (8) increases, so that the same result is likely to occur. Therefore, as the fifth transistor (8), a transistor having a small saturation voltage and maintaining a sufficient h _FE even in a region where V _CE is extremely lowered is desired.

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

FIGS. 1A and 1B are cross-sectional views showing such a lateral PNP transistor, showing an N-type epitaxial layer (32) formed by stacking on a P-type semiconductor substrate (31) and a substrate (3).
1) N ⁺ type buried layer (33) buried on the surface and this buried layer (3
3) P that penetrates the epitaxial layer (32) so as to surround it
^{A +} type isolation region (34), an island region (35) separated into islands by the isolation region (34), a P type emitter region (36) formed on the surface of the island region (35), and an emitter Area (3
6) A P-type collector region (37) facing each other and spaced apart from each other, an emitter region (36) and a collector region (37)
N ⁺ type guard ring region (3
8) composed of a base that is active as a transistor
The junction lengths of the emitter junction and the base-collector junction are made approximately equal. The guard ring region (38) is shared as a contact for the island region (35) serving as a base, and is formed in a ring shape to prevent leakage current from the emitter region (36) and the collector region (37) to the isolation region (34). Has been formed. At this time, the high-concentration guard ring region (38) comes into contact with the respective regions to deteriorate the breakdown voltage, but there is no problem if it is used at a low power supply voltage as in the present invention. Further, in this embodiment, in order to almost completely prevent the leakage current to the isolation region (34), it is formed as a diffusion region reaching from the surface of the island region (35) to the buried layer (33) as a guard ring region (38). But
It may be formed shallower than this, for example, in the same diffusion region as the collector contact region (28) of FIG. 7.

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.
The efficiency of reverse injection of holes from the collector to the base when the collector junction is forward biased is small. Therefore, even the same forward bias applied, because towards those of the present invention is small is reverse injection of holes from the collector to the base for the injection amount of holes from the emitter to the base, the collector current I _C caused by their difference Can be drained more,
The saturation voltage V _CE (sat) can be relatively lowered. It is possible to take this a step further and shorten the junction length of the collector-base junction with respect to the emitter-base junction.
It is not preferable because h _FE cannot be taken in the active region.

3A and 3B show the transistor characteristics of the invention of FIG. 1 and the conventional one of FIG. 7, respectively. As is clear from the figure, since the present invention has an excellent I _C rising characteristic, the conventional one has V _CE = 5 when Ib = 1 [μA].
At 0 [mV], h _FE = 10 at last, whereas in the present invention, when Ib = 1 [μA], V _CE = 35 [mV] already exceeds h _FE = 10. In the saturation region where V _CE is extremely reduced, reverse injection of holes from the collector to the base is superior, and the leakage current due to the parasitic PNP transistor with the substrate (31) cannot be ignored. Current flows in the opposite direction to.

Now, in the circuit diagram of FIG. 2, when V _CC = 1.5V, the reference voltage is set sufficiently high to 0.90V, and when V _CC drops to 1.0V, the power ripple of maximum amplitude −0.04V is superimposed. Assuming that, only the residual voltage 0.06V is applied to V _CE of the fifth transistor (8). V _CE = 0.
Comparing FIG. 3A and FIG. 3B at 06V, the conventional one is completely in the saturation region, whereas the present one still maintains a certain h _FE. I understand. Fifth
If the transistor (8) keeps some h _FE , this ripple filter can keep the power ripple removed. Therefore, according to the present invention, it is possible to provide a ripple filter in which the ripple removal rate is excellent due to the decrease in the saturation voltage, and thereby the output voltage can be set sufficiently high.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention,
( 41 ) is a differential amplifier circuit having first and second transistors (42) and (43) whose emitters are commonly connected, ( 44 )
Is a bias circuit that applies a reference voltage obtained at the connection midpoint of the first and second voltage dividing resistors (45) and (46) to the base of the first transistor (42), and (47) is the first transistor ( 42) a first current inverting circuit for inverting the collector current, (48) a second current inverting circuit for inverting the collector current of the second transistor (43), (49) a first current inverting circuit ( 47 ) A third current inverting circuit for further inverting the output current of the above, (50) to (52) are third to fifth transistors for amplifying the difference current between the second and third current inverting circuits ( 48 ) and ( 49 ), (53) is a detection transistor for saturation detection, the emitter of which is connected to the collector of the third transistor (50) and the base of which is connected to the collector of the fourth transistor (51), and (54) is the detection transistor (53). Control tiger controlled by the output signal of It is a register. still,
(55) is an output terminal, and (56) is a ripple removing capacitor.

The second embodiment of the present invention is characterized in that a detection circuit for detecting the saturation of the output transistor and a means for lowering the reference voltage according to the output signal of the detection circuit are provided.

In a normal operation state in which the fifth transistor (52) is not saturated, the _hFE (current amplification factor) of the fifth transistor (52) is high, so that the base current becomes small and the base voltage of the detection transistor (53) is high. To be kept. Also, the third
Since the collector voltage of the transistor (50) is low, the emitter voltage of the detection transistor (51) is also kept low. Therefore, the detection transistor (53) does not turn on, and the control transistor (54) does not turn on either.

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

As the fifth transistor (52), the lateral PNP shown in FIGS. 1A and 1B is provided as a feature of the present invention.
It uses a transistor. According to the present embodiment, even if the fifth transistor (52) is saturated, the circuit is configured to release it, so that the ripple removal rate during normal operation is excellent, and when an excessive ripple or an increase in load current occurs. Since the deterioration of the ripple removal rate can be prevented, the output voltage in the normal operation can be set to the maximum, and the saturation voltage of the fifth transistor (52) is small, so that the output voltage can be set higher. Moreover, according to the present embodiment, since the ripple rejection ratio is excellent, for example, when V _CC = 1.5V, I
It's also very easy to integrate into C.

5A and 5B are a cross-sectional view and a plan view, respectively, for explaining a third embodiment of the present invention, showing a reverse conductivity type formed by laminating on a surface of a single conductivity type semiconductor substrate (31). N ⁺ formed by embedding on the epitaxial layer (32) and the surface of the substrate (31)
Type buried layer (33) and a P ⁺ -type isolation region (3) penetrating the epitaxial layer (32) so as to surround the buried layer (33).
4), an island region (35) formed in an island shape by the separation region (34), and a P-type emitter region (36) and a collector region (37) alternately arranged apart from each other on the surface of the island region (35). )When,
The emitter region (36) and the guard ring region (38) are formed so as to collectively surround the collector region (37), and the emitter regions (36) are arranged at both ends.
The emitter region (36) and the collector region (37) have the same shape,
They are formed in the same size, and their separation distances (base widths) are also the same. In the lateral PNP transistor thus formed, the junction lengths of the base-emitter junction and the base-collector junction, which are active as transistors, are approximately equal, but the emitter region (36) is arranged at both ends, so that the guard ring region (38) Hole injection from the emitter to the base that cannot be prevented acts, and it is equivalent to increasing the base-emitter junction length as a result. Therefore, the saturation voltage in the lower voltage region becomes smaller than that of the lateral PNP transistor of FIG.

If the above-mentioned transistor is used as the output transistor, a ripple filter with further improved characteristics can be constructed by the first and second embodiments.

(G) Effect of the Invention As described above, according to the present invention, the ripple filter that is excellent in the normal state, has a small deterioration in the ripple removal rate even when the voltage is reduced, and can set the output voltage sufficiently high. Has the advantage that Also, since the output voltage can be set high enough, it has excellent voltage reduction characteristics and is
Also, it has an advantage that a suitable ripple filter can be provided for use in a device using a low power supply voltage of 3.0 V. Further, according to the second embodiment of the present invention, there is an advantage that the ripple rejection ratio does not deteriorate even when the ripple is excessive or the load current increases, and the ripple filter in which the output voltage is set higher can be provided. According to the present invention, since no additional process is required to construct the lateral PNP transistor of FIGS. 1 and 5, the ripple removing capacitor (1
Except for 1), it is possible to configure a ripple filter that can be adapted to ICs, and especially in terms of Ic max, there is an advantage that a ripple filter with good characteristics can be configured even when an external transistor is connected in parallel with the fifth transistor (8). .

[Brief description of drawings]

1A and 1B are lateral PNs used in the present invention.
The top view and sectional drawing which show a P transistor, FIG. 2 is the circuit diagram which shows the ripple filter of this invention, FIG.
FIG. B is a transistor characteristic diagram of a lateral PNP transistor used in the present invention and a conventional lateral PNP transistor, respectively. FIG. 4 is a circuit diagram showing a second embodiment of the present invention, and FIG.
FIGS. A 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, and FIGS. 7A and 7B. 7 Figure B
FIG. 8A is a plan view and a cross-sectional view showing a conventional lateral PNP transistor, and FIGS. 8A to 8C are characteristic diagrams for explaining the ripple removal rate. ( 3 ) 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.

Claims (1)

[Claims] 1. A ripple filter incorporated in an IC for electronic equipment driven by a power supply having a reduced voltage characteristic, the 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, an output transistor for current-amplifying the output signal of the differential amplification circuit, and a ripple removal capacitor connected to the base of the first transistor A ripple filter formed by feeding back the output signal of the output transistor to the base of the second transistor, and an island formed by not selling an epitaxial layer of a reverse conductivity type formed on a semiconductor substrate of a single conductivity type. A region is a base region, and one conductivity type emitter region formed in a stripe shape on the surface of the base region, and a strike of the emitter region. A striped one conductivity type collector region also formed on the surface of the base region so as to extend parallel to the base region, and a PN junction formed between the emitter region and the collector region and the base region. A PN junction that surrounds the emitter region and the collector region while contacting a PN junction in which the emitter region and the collector region do not face each other, and the PN that faces the emitter region and the collector region.
A ripple filter, wherein junction lengths are made substantially equal to each other, the base region serves as a base of the output transistor, the emitter region serves as an emitter of the output transistor, and the collector region serves as a collector of the output transistor.