JPS5921205B2 - power amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to an improvement of a 5EPP type power amplifier suitable for integration into an integrated circuit.

As is well known, in this integrated circuit, it is particularly difficult to create a PNP transistor for single current.

Therefore, 5EPP (single-ended push-pull)
Conventionally, when integrating a type of power amplifier into an integrated circuit, the
As shown, N is responsible for the positive half cycle of the signal period.
PN transistor as NPNl-transistor Qt
, Q2 is used with Darlington connection (this,
An NPN1-transistor Q4. serves as a PNP transistor in charge of the negative half cycle. A small current PNP t-transistor Q3 is connected to a Darlington connected transistor Q5 to form an equivalent single current PNP transistor.

In the figure, Qll, Q, 2 are input differential pair transistors, Q10 is a drive transistor, DI, t
This is a bias diode for determining idle current.

However, such a circuit configuration (in this case, the equivalent P
When a parasitic feedback loop is formed with the emic of Q3 that constitutes the NP t-transistor → collector → base of Q4 → base of Q5 → collector → emitter of Q3, a parasitic feedback loop is formed and the gain band of the integrated circuit PNP transistor is Undesirable oscillations are likely to occur due to the low width product fT.

For this reason, it is safe to suppress oscillation by connecting individual components such as capacitors outside the integrated circuit.

Therefore, the advantages of integrated circuits aimed at reducing the number of parts and costs tend to be lost.

Therefore, this invention was made in view of the above points, and in order to perform high-frequency phase correction (the inserted resistor cancels out the generation of negative resistance in the parasitic feedback loop and eliminates the negative resistance). In addition to suppressing oscillation in the desired feedback loop (
In order to prevent parasitic oscillations, the first and second capacitors are inserted to stabilize the high frequency range, so that even if a third capacitor is inserted, the stability will not be bypassed. An extremely good 5EP that can improve the performance and take advantage of the benefits of integrated circuits.
The purpose is to provide a P-type power amplifier.

That is, as shown in FIG. 2, the input terminal IN is connected to the input stage differential pair transistor Q21 . Q2
One side of □ is connected to the base of Q21.

Here, the base of the transistor Q21 is connected to the resistor R11~
R13, diode Dll j D12, capacitor C
A predetermined base bias is applied by a bias circuit consisting of I2C13 and transistors Q23 to Q25.

Further, the differential pair transistors Q21 and C22 have a current source transistor Q26 interposed between their common emitters and the positive power supply line +VL, and a current source transistor Q26 between their respective collectors and the negative power supply line -VER.
A transistor Q27 constituting a current inversion circuit,
The base of the other transistor Q22 is connected to the output terminal 0UTl through a resistor R14, and is connected to the negative power supply -V through a capacitor CI4 and a resistor R15 in series. The collector of one transistor Q21 is the drive stage transistor Q.
Connected to the base of 3o.

The drive stage transistor Q30 has its emitter connected to the negative power supply -VBBf, and its collector connected to the cathode side of the three cascaded diodes D13 to D15 for determining the idle current via the high frequency correction resistor R16. Capacitors C16 and C1□ are connected between the base and collector and between the collector and emitter of t for the purpose of preventing oscillation due to a parasitic feedback loop, which will be described later.

In addition, the three cascaded diodes DI3 for determining the idle current
~D15 has its cathode side connected to the base of a small current PNP transistor Q31 constituting an equivalent PNP l-transistor, and its anode side connected to the equivalent bases of Darlington-connected NPN transistors Q34 and C35.

Both E and the positive power supply line VLf are connected via the current source transistor Q36.

Here, the equivalent PNP transistor is an NPN transistor Q3□ in which the small current PNP transistor Q31 is connected to Darlington.

It consists of being connected to the special price base of C33.
・The emitter of C31 and the collector of Qa3'' are connected to the output terminal 0UTf, the collector of C3□ is connected to the positive power supply 1 V (1), and the emitter of Qaa is connected to the negative power supply - connected to.

Also, the Darlington connected NPN transistor Q3
45 C35 has an equivalent collector whose positive power supply +V(1)l
When this is connected, it is connected to the positive power supply line +vL via the resistor R17, and its equivalent emitter is connected to the output terminal OUT.
#This is connected.

In the above configuration, C31 constitutes an equivalent PNP transistor that suppresses the negative half cycle of the signal period.
Even if parasitic feedback is formed, such as the emitter of Q32 → the base of Q32 → the emitter of Q32 → the base of Q33 → the collector of Q31 → the emitter of Q31, for high-frequency correction (the collector of the drive stage transistor Q3o and the idle The resistor R16f inserted between the current determining elements (diodes D13 to D15) causes phase rotation in the feedback loop, but cancels out the negative resistance generated therein and prevents undesired oscillations. This invention is characterized in that it is possible to prevent this and improve stability.

Furthermore, even if capacitor CI5 is inserted between the base and collector of C31 for the purpose of stabilizing the high frequency range, since resistor R16 is inserted at the base of Q31, the base and collector of drive stage transistor Q30 and Capacitor C1 inserted between collector emitter for the purpose of preventing oscillation, etc.
Since the 65C17f is not bypassed, its effect can be fully exhibited.

The effect of preventing oscillation due to the resistor R161 is due to the resistance of the Darlington connection N, which is responsible for the positive half cycle of the signal period.
The same effect can be achieved for the PNl-transistor Q34 and C35E.

That is, in effect, N operates as an emitter follower.
Since the signal source impedance of the PNt transistor Q34) C35 can be suppressed from becoming low impedance and capacitive in the high range due to the aforementioned capacitor C10, etc., by the resistor R16, parasitic oscillation of the emitter follower can be prevented. It is possible.

By the way, although the insertion of the resistor R16 prevents the base potential of Q3t from dropping to the negative power supply voltage -VEE voltage, this does not substantially cause any inconvenience.

That is, originally Qst, the collector is C32t C
This is because the long-term base-to-emitter voltage (C) of approximately 1.2 to 2 V in the case of a silicon transistor is required.

Rather, if the base potential of C30 drops too much below its collector potential, Qao will be saturated and minority carriers will pass through, which is not preferable.

In consideration of this point, it is desirable to set the value of the resistor R16 so as to suppress the Qst to just before saturation or to the extent that it is slightly saturated.

In addition, the idle current is determined only by the diodes D13 to D15, C31, C34, C35, and E, which are the determining elements, and the resistor IRta is irrelevant, so in this point as well, the idle current does not affect the current.

In this case, if the collector of the drive stage transistor Q30 and the diodes D13 to D15 for determining the idle current are directly connected, and the corresponding resistor is inserted between the connection point and the base of C31, the idle current will change accordingly. This is not preferable because when the output current changes, the potential change at both ends becomes large.

FIG. 3 shows another embodiment, in which resistor R16
A diode D' for level shifting is inserted between the base of Q31 and an appropriate number of diodes D1 for determining the idle current, and an appropriate number of diodes D are inserted between the emitter of C31 and the output terminal OUT. ■ has been inserted.

Furthermore, I. 1 j IO21IO3 is a current source, and the other parts are constructed in the same manner as the output section 1 shown in FIG.

According to this configuration, the equivalent base-emitter potential VBE of C31, C34, C35 and the ridges is DI
and D■ equivalent base-emitter potential VB B
Therefore, if an idle current is caused to flow through D', the design of DI and DII becomes easier, and the output amplitude of E can be increased.

It goes without saying that the same effect can be obtained even if the polarity of the transistors used and the polarity of the power supply are switched in the above description, and that the present invention can also be applied to a so-called pure complementer IJsEPP power amplifier.

Therefore, as described in detail above, according to the present invention, in order to perform high-frequency phase correction, the generation of negative resistance in the parasitic feedback loop is canceled out by the inserted resistor, resulting in undesirable effects. The first and second capacitors are inserted to suppress oscillation in the feedback loop and prevent parasitic oscillations.Thus, even if a third capacitor is inserted for high frequency stabilization, the E From rubbing,
It becomes possible to provide an extremely good 5BPP type power amplifier that has been improved to improve stability and to take advantage of the advantages of integrated circuits.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram showing a conventional 5EPP power amplifier, Fig. 2 is a wiring diagram showing one embodiment of a 5EPP power amplifier according to the present invention, and Fig. 3 is a wiring diagram showing another embodiment. FIG. C30...drive stage transistor, R16...
... Resistor, D13 to D15 ... Idle current determining diode, C31, C32, C33...
...(equivalent PNP) l-transistor, C34, C35
・・・・・・Darlington connected NPN transistor, C
15~C17...Capacitor.

Claims (1)

[Claims] 1. At least an equal current NPN transistor that is responsible for the positive half cycle, and an equal current NPN transistor that is responsible for the negative half cycle and is configured by combining a small current PNP t-transistor with an NPNI-lanosk; A 5EPP type power amplifier comprising a drive transistor that commonly drives the equivalent large current NPN and PNP transistors, and a bias element that determines a common idle current. first and second capacitors connected between the base and the collector and between the collector and emitter of the drive transistor, and the collector of the drive transistor and the AiJ.
A resistor is interposed and connected between the bias element for determining the idle current, and a third capacitor is connected between the base and the collector of the small current PNP I transistor, and the bias element and the third capacitor are connected. A SEPP type power amplifier characterized in that a connection point with a resistor is directly connected to the base E of the PNP t-transistor for small current.