JPH0618296B2 - Push-pull amplifier circuit - Google Patents

Description

The present invention relates to a push-pull amplifier circuit, and more particularly to a push-pull amplifier circuit with greatly improved voltage reduction characteristics.

(B) Conventional technology As a push-pull amplifier circuit driven by a low-voltage power supply,
For example, there is one described in Japanese Patent Application No. 59-228309.

FIG. 4 shows such a circuit, where (1) is an input terminal to which an input signal is applied, (2) and (3) are NPN first and second drive transistors, and ( 4 ) is a current source (5). Constant current source consisting of transistor and transistors (6) and (7), ( 8 ) is current source (5) and transistors (6) and (9)
And a second constant current source (10), a base of which is connected to the collector of the first drive transistor (2) and a PNP first output transistor (11) whose base is the second drive transistor (3). ) The second output transistor of NPN type connected to the collector, (12) is the output capacitor (13) at the output point A.
The speaker is a load that is connected via the.

In FIG. 4, the current flowing through the current source (5) is I ₀ ,
If the mirror ratio is set to 1, the collector currents of the transistor (6) and the transistors (7) and (9) connected in the current mirror connection are I respectively.
It becomes ₀ . When the base biases of the first and second drive transistors (2) and (3) are set to predetermined values, their collector currents can be set to I ₀ . Therefore, in the non-signal state where no input signal is applied to the input terminal (1),
Since the first and second drive transistors (2) and (3) respectively draw the output current I ₀ of the second constant current sources ( 4 ) and ( 8 ) respectively, the first and second output transistors (10) and (11) are Turn off. And input terminal
When a positive input signal is applied to (1), the collector currents of the first and second drive transistors (2) and (3) increase, and I ₀ + Δ
I, and the base current of the first output transistor (10) ΔI
Flows, this turns on, and the second output transistor (11) is O
FF. On the other hand, when a negative input signal is applied to the input terminal (1), the collector currents of the first and second driving transistors (2) and (3) decrease to I ₀ −ΔI, and the second output transistor ( 11) Base current ΔI flows and this turns on,
The output transistor (10) turns off.

FIG. 5 shows N used in the push-pull amplifier circuit of FIG.
Shows the structure of PN type transistor, P type semiconductor substrate (21)
The N-type epitaxial layer (22) formed by stacking on it, the N ⁺ -type buried layer (23) buried in the surface of the substrate (21), and the P ⁺ -type isolation region (that penetrates the epitaxial layer (22) ( Island region (25) formed by junction separation by 24), P type base region (26) formed on the surface of the island region (25), and N ⁺ type emitter region (27) formed on the surface of the base region (26). ), An N ⁺ -type collector contact region (28), and an oxide film (2) covering the epitaxial layer (22).
9) and an electrode (30) which makes ohmic contact with each region through a contact hole having an oxide film (29) formed therein.

Such a push-pull amplifier circuit has a base-emitter voltage V _BE of a drive transistor and a voltage drop V _CE (sa of a constant current source).
It is useful for operating at a power supply voltage V _CC that is equal to or higher than the sum voltage of t).

(C) Problems to be Solved by the Invention However, in the conventional push-pull amplifier circuit, when driven by a power supply whose power supply voltage V _CC decreases depending on the usage time or usage conditions, the power supply that has dropped extremely There is a drawback that the voltage V _CC does not operate normally or the time comes early.

In FIG. 4, assuming that the power supply voltage V _CC drops to 0.8 V, for example, when the second output transistor (11) is turned on, the second output transistor (3) is connected between the collector and the emitter of the second drive transistor (3). 11) V _BE (= 0.65)
V) is applied and can be operated in high h _FE conditions. However, when the first output transistor (10) is turned on, there is a potential drop of V _BE of the first output transistor (10) between the collector and the emitter of the first drive transistor (2), so that V _CC -V _BE. Only (= 0.15V) is applied, and h _FE is extremely lowered. And the power supply voltage V _CC
The first output transistor (1
The ability to draw the base current of 0) is lost, and a predetermined output signal current cannot flow.

If, if h _FE of the first driving transistor (2) is defined as loss of ability to flow a predetermined value or more output signal currents at forme drop to about 30, in the transistor of the structure shown in FIG. 5 V _The limit is _CE = 0.11V. Therefore, in the conventional push-pull amplifier circuit, the power supply voltage V _CC is V _BE + V _CE = 0.
The operating limit is reached when the voltage drops to 76V.

Furthermore, since the first and second drive transistors (2) and (3) operate with different h _FE , there is a drawback that the distortion characteristic deteriorates as the power supply voltage V _CC decreases.

(D) Means for Solving the Problems The present invention has been made in view of the above drawbacks, and the first and second drive transistors (2) and (3) are formed on the surface of the island region (35) serving as a collector. A P ⁻ -type active base region (36), an N ⁺ -type emitter region (37) formed on the surface of the active base region (36), and a base contact region (3 that partially overlaps the active base region (36).
8) A push-pull amplifier circuit with greatly improved voltage reduction characteristics is provided by using the transistor formed in and.

(E) Function The transistor of the structure used in the present invention has the base formed of the low-concentration active base region (36), so that the current rising characteristic of the emitter-base junction is better than that of the conventional transistor, and the carrier at the base is High transportation efficiency. Therefore, even if the collector potential is insufficient, it is highly likely that minority carriers (electrons) will be injected from the emitter and reach the collector.
High h _FE is maintained even in the region where the collector-emitter voltage is low.

Therefore, according to the present invention, since such a transistor is used for the first and second driving transistors (2) and (3), it is possible to normally operate even in a region where the power supply voltage V _CC is considerably lowered.

(F) Example Hereinafter, one example of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a push-pull amplifier circuit according to the present invention,
(1) is the input terminal to which the input signal is applied, (2) is the input terminal
A first drive transistor of NPN type whose base is connected to (1), (3) is a second drive transistor whose base and emitter are commonly connected to the base and emitter of the first drive transistor (2), and ( 4 ) is A first constant current source consisting of a current source (5), a diode-connected transistor (6), and a transistor (7) that is current-mirror connected to this transistor (6), and ( 8 ) is a current source (5) and a diode. Connection-type transistor (6) and transistor with current mirror connection to this transistor (6)
(9) is a second constant current source, and (10) is a PNP type that operates according to the difference current between the collector current of the first drive transistor (2) and the output current of the first constant current source ( 4 ). A first output transistor, (11) is an NPN type second output transistor which operates according to a difference current between a collector current of the second drive transistor (3) and an output current of the second constant current source ( 8 ), (12 ) Is a speaker which is a load connected to the output point A of the push-pull amplifier circuit via the output capacitor (13).

In the figure, if the current flowing through the current source (5) is I ₀ and the mirror ratio is 1, the output currents of the first and second constant current sources ( 4 ) and ( 8 ) are I ₀ , respectively. If the base biases of the first and second drive transistors (2) and (3) are set to predetermined values, the collector currents of these can be set to I ₀ . Therefore, in the non-signal state in which the input signal is not applied to the input terminal (1), the output current of the first constant current source ( 4 ), the collector current of the first drive transistor (2), and the second current
The output current of the constant current source (8) and the collector current of the second drive transistor (3) become equal to each other, the base currents of the first and second output transistors (10) and (11) do not flow, and both transistors are turned off. To do.

Next, when a positive input signal is applied to the input terminal (1), the collector currents of the first and second driving transistors (2) and (3) increase to I ₀ + ΔI, and the first output △ to transistor (10)
The base current of I flows and the first output transistor 10 is turned on. At that time, since the output current of the second constant current source ( 8 ) all flows into the collector of the second drive transistor (3),
The second output transistor (11) is turned off. Therefore, the collector current of the first output transistor (10) flows into the speaker (12) as an output signal current, and a sound corresponding to a positive input signal is generated from the speaker (12). The output signal current I _OUT at this time is I _OUT = I _IN · h _FE1 · h _FE2 ………… (1) Becomes Since it is difficult to increase h _FE of the PNP transistor when integrated into an IC, a large output signal current I _OUT
It can be seen that it is desired to make h _FE of the first drive transistor (2) as high as possible in order to obtain

On the other hand, when a negative input signal is applied to the input terminal (1), the collector currents of the first and second drive transistors (2) and (3) decrease to I ₀ −ΔI, and the second output transistor (2) The base current of ΔI flows to the base of 11), and the second output transistor
(11) turns on. At that time, since the output current of the first current source ( 4 ) becomes larger than the collector current of the first drive transistor (2), the first output transistor (10) is turned off. Therefore, the collector current of the second output transistor (11) flows to the speaker (12) as an output signal current, and the speaker (12) produces a sound corresponding to the negative input signal. Therefore, if the push-pull amplifier circuit of FIG. 2 is used, a speaker that becomes a load according to the positive and negative input signals applied to the input terminal (1)
(12) can be driven, and the first and second driving transistors (2) and (3) are characterized in that the base is a low concentration active base region (3).
The transistor formed in 6) is used.

FIG. 1 shows such a transistor, and a P-type semiconductor substrate (31)
The N-type epitaxial layer (32) formed by stacking on it, the N ⁺ -type buried layer (33) buried in the surface of the substrate (31), and the P ⁺ -type isolation region (34) make the epitaxial layer (32) An island region (35) which becomes a collector formed by junction separation, a P ⁻ -type active base region (36) formed on the surface of the island region (35), and an active base region (3
6) N ⁺ type emitter region (37) formed on the surface and base contact region (38) partially overlapping the active base region (36)
And N ⁺ collector contact region (39) and oxide film (40)
And an electrode (41) which makes ohmic contact with each region through a contact hole opened in the oxide film (40). The base contact region (38) is formed so as to surround the emitter region (37) in order to lower the base extraction resistance, and the active base region (36) may be shallower and deeper than the base contact region (38). However, it goes without saying that a diffusion depth deeper than the emitter region (37) and sufficient to obtain a predetermined breakdown voltage is required. The base contact region 38 is formed in the base diffusion process of the NPN transistor, and the emitter region 37 and the collector contact region 39 are formed in the emitter diffusion process of the NPN transistor. And the active base region (3
The impurity concentration of 6) is lower than that of the base contact region (38),
It is about 10 ¹⁶ cm ^-3 .

Since the transistor thus formed uses the low-concentration active base region (36) for the base, the current rising characteristic of the emitter-base junction is better than that of the conventional transistor, and the carrier transport efficiency at the base is high. Therefore, even if the collector potential is insufficient, the probability that minority carriers (electrons) injected from the emitter reach the collector is high, and h _FE is high in the saturated region as well as high in the non-saturated region where V _CE is low. You can keep _FE .

FIGS. 3A and 3B show V _CE -I _C characteristic diagrams of the transistor of FIG. 1 and the transistor of FIG. 5, respectively. As is clear from the figure, in the transistor of FIG. 5, V _CE = 0.11 V already drops to h _FE = about 30, whereas in the transistor of FIG. 1, V _CE = 0.11 V and h _FE is still. = Keep about 160. If equation (1) is used, h _FE (h of the first drive transistor (2) (h
If it becomes impossible to flow the current I _OUT with an output signal of a predetermined value or more (operation limit) when _FE1 ) drops to about 30,
In the transistor of FIG. 5, V _CE = 0.11 V is the lower limit, and the minimum operating power supply voltage V _CC is 0.65 + 0.11 = 0.
It becomes 76V. On the other hand, in the transistor shown in FIG. 1, since h _FE = 30 or more is maintained until V _CE = 0.05 V, the push-pull amplifier circuit according to the present invention has a power supply voltage V _CC of 0.6.
It becomes operable until it drops to 5 + 0.05 = 0.70V.

Further, since the first drive transistor (2) keeps high h _FE until the power supply voltage V _CC is considerably lowered, the first and second drive transistors (2) and (3) are different in h _FE when the voltage is reduced. The distortion characteristics of the output signal waveform due to the operation are significantly improved. Moreover, the transistor of FIG.
Since the rise of I _C is steeper than that in the figure, a good distortion characteristic is exhibited up to near the above-mentioned operating limit. In the present invention, the second
The transistor shown in FIG. 1 is used as the driving transistor (3) so that the characteristics of the first and second driving transistors (2) and (3) are made equal when the power supply voltage V _CC is kept at a sufficient value. This is because.

Further, as another embodiment of the present invention, the transistor of FIG. 1 can be used as the second output transistor (11) in addition to the first and second drive transistors (2) and (3). in this case,
The transistor of FIG. 1 has a large current drawing capability even when V _CE is low, and therefore has an advantage that an output with a larger amplitude waveform can be obtained.

(G) Effect of the Invention As described above, according to the present invention, the bases of the first and second driving transistors (2) and (3) are formed in low concentration active base regions (36).
Since the transistor formed in 1) is used, it has an advantage that it can be operated up to a considerably lowered power supply voltage V _CC . Moreover, because it keeps high h _FE up to the operating limit,
First and second drive transistors (2) (3) at reduced voltage
Have the advantage that the distortion characteristics of the output signal waveform due to the operation of different h _FE can be significantly improved. Furthermore, the transistor of FIG. 1 only needs to add a diffusion step of the active base region (36) to a normal NPN transistor, so that it is efficient only for a specific transistor on the same chip without increasing the chip area. It has the advantage that it can be formed.

[Brief description of drawings]

1 and 2 are a sectional view and a circuit diagram respectively for explaining the present invention, and FIGS. 3 (a) and 3 (b) are V _CE -I _{C of a} transistor.
A characteristic diagram, FIG. 4 and FIG. 5 are a circuit diagram and a sectional view for explaining a conventional technique, respectively. (2) and (3) are first and second drive transistors, (10) and (11) are first and second output transistors, (31) is a P-type semiconductor substrate, and (3)
5) is an island region, (36) is a P ⁻ type active base region, (37) is an N ⁺ type emitter region, and (38) is a P type base contact region.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Bibliography Sho 58-119219 (JP, U) "Introduction to VLSI" by Kuniichi Ota, Ohm Co., Ltd., 1st edition issued January 30, 1983 Line, P82-83 "Latest Electronic Device Encyclopedia", Gen Baba, Radio Technology Co., Ltd., first edition issued March 20, 1976, P174 "Latest Semiconductor Term Dictionary", edited by Motoaki Tokita, CQ Publishing Co. Company, March 5, 1973, 4th edition, P55

Claims (1)

[Claims] 1. A grounded-emitter first driving transistor whose base is connected to an input terminal, and a grounded-emitter second driving transistor whose base and emitter are connected to the base and emitter of the first driving transistor, respectively. A PNP first output transistor driven by a signal obtained from the first drive transistor;
In a push-pull amplifier circuit including an NPN type second output transistor driven by a signal obtained at the collector of the driving transistor, the first and second driving transistors are one conductivity formed on the surface of the island region serving as the collector. Type low concentration active base region, a reverse conductivity type emitter region formed on the surface of the active base region, and a one conductivity type base contact region partially overlapping with the base region, and a power supply voltage Is applied by means having a voltage reduction characteristic that decreases with use time.