JPS588602B2 - Denryokuzoufukuki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in power amplifiers used in radio receivers and the like.

FIG. 1 shows a conventional power amplifier of this type.

In the figure, 1 is an input transformer with a primary coil 1a and a secondary coil 1.
It has b.

2 is an output transformer, which has a primary coil 2a and a secondary coil 2b.
The middle point of the primary coil 2a is connected to a power supply +Vc terminal, and the secondary coil 2b is connected to a load 3 such as a speaker.

Q3 and Q4 are NPN type output transistors, Q1 and Q2
is an NPN type transistor that drives this output transistor.

For example, as shown in FIG. 2, these NPN type transistors include an N type epitaxial layer 12 which serves as a collector region on a P type substrate 11, which is separated by a P type isolation layer 13, and then a P type base region. 14 is formed by diffusion, an N-type emitter region 15 is further formed by diffusion, and a collector electrode 16, an emitter electrode 17, and a base electrode 18 are formed on the Sin2 film 19.

As shown in FIG. 3, the impurity concentration in each region is the lowest in the N-type collector region, the highest in the N-type emitter region, and the impurity concentration in the P-type base region is intermediate therebetween.

In the transistors Q3 and Q4, the collector regions with the lowest impurity concentration are connected to both ends of the primary coil 2a of the output transformer 2, and the emitter regions with the highest impurity concentration are both connected to the resistor R.
It is grounded via 2.

The collector regions of the transistors Q1 and Q2 with the lowest impurity concentration are both connected to the power supply +Vc terminal, and the emitter regions with the highest impurity concentration are connected to the transistors Q3 and Q4, respectively.
connected to the base area of the

Both ends of the secondary coil 1b of the input transformer 1 are connected to base regions of transistors Q1 and Q2, respectively.

The semi-fixed resistor R1 and the diodes D1 and D2 provide DC bias to the transistors Q1 and Q2.The connection point between the resistor R1 and the diodes D1 and D2 is connected to the secondary coil 1b of the transformer 1, and this secondary coil 1b A DC bias is applied to transistors Q1 and Q2 through the transistors Q1 and Q2.

This power amplifier converts the input signal current into transistor Q1
, Q3 each base, emitter region or transistor Q
2 and Q4 through the base and emitter regions, and the power is amplified.

By the way, N used as transistors Q1 to Q4
The cutoff frequency of PN transistor is usually 400MHz
When the power amplifier shown in Figure 1 is used in a radio receiver, the RF frequency of the radio receiver is included within the cutoff frequency of the NPN transistor, so the high frequency noise of the transistor is radiated to the antenna of the radio receiver. , resulting in an unpleasant sound.

This phenomenon is commonly called radiation.

Conventionally, in order to prevent and reduce this radiation, the output stage including the power amplifier and the antenna are placed apart from each other.
Efforts have been made to intentionally use PNP transistors with poor high frequency characteristics in power amplifiers, and to shield the space between the output stage and the antenna, but these have the disadvantage of making the set larger and more expensive.

The present invention provides a power amplifier that can easily prevent and reduce radiation without such inconveniences.

FIG. 4 shows an embodiment of the inventive device, in which the same parts as in FIG. 1 are denoted by the same reference numerals.

The feature of this invention lies in the configuration of transistors Q1 and Q2.

These transistors Q1 and Q2 are the same as those in FIG.
Although they are NPN transistors, the emitter regions with the highest impurity concentration are connected to the power supply +Vc terminal, and the collector regions with the lowest impurity concentration are connected to the output transistor Q.
3 and Q4, respectively.

That is, instead of connecting the collector, base, and emitter of a conventional NPN transistor as they are, the collector is used as an emitter, and the emitter is used as a collector, that is, the transistor is used as a reverse transistor.

The configurations of output transistors Q3 and Q4 are the same as in FIG. 1, and the emitter region with the highest impurity concentration is connected to the resistor R2.
The collector regions having the lowest impurity concentration are connected to both ends of the primary coil 2a of the output transformer 2, respectively.

In other respects, the embodiment of FIG. 4 is constructed the same as that of FIG.

As for the transistors Q1 and Q2, the embodiment of FIG. 4 has the result that the emitter region and the collector region are just replaced and connected to each other, compared to the transistors Q1 and Q2 of FIG. 1.

In the embodiment of FIG. 4, the input signal current flows through the base, collector region of transistor Q1 and the base, emitter region of transistor Q3, or the base, collector region of transistor Q2 and the base, emitter region of transistor Q4. Example drive transistor Q1
, Q2's collectors actually operate as emitters.

In other words, if it operates like a normal collector, the current will flow in the direction of flowing into the drive transistors Q1 and Q2, and the current will not be able to be supplied to the output transistors Q3 and Q4, so this circuit will not operate. The same function as the conventional power amplifier circuit shown in FIG. 1 is achieved only when the drive transistors Q1 and Q2 operate as inverse transistors and their collectors function as emitters.

In this case, between the base and collector of the transistors Q1 and Q2, the carrier transfer time within the base region of electrons injected from the collector region to the base region becomes slow due to the low impurity concentration in the collector region. As a result, most of the recombination occurs within the base region, and as the current amplification factor decreases, the cut-off frequency of transistors Q1 and Q2 decreases, and radiation can be significantly reduced.

When components other than the input/output transformers 1 and 2 are configured with semiconductor integrated circuits, the configuration shown in Figure 3 can be achieved by simply changing the wiring pattern on the insulating film covering the semiconductor substrate, and the configuration is extremely simple. It's easy.

Conventionally, there is a power amplifier circuit equipped with a drive transistor and an output transistor of the opposite junction type (see Japanese Patent Laid-Open No. 49-42266), but this conventional device has a drive transistor and an output transistor. The condition is that they have opposite junction types, and if both are NPN junction types like the device of the present invention, it will not work, which is completely different from the present invention.

As described above, the device of the present invention has the effect of preventing and reducing radiation without easily increasing the size of the set.

[Brief explanation of the drawing]

Figure 1 is an electrical circuit diagram of a conventional power amplifier, Figure 2 is an NP
FIG. 3 is an explanatory diagram showing the impurity concentration of each region of the N-type transistor, and FIG. 4 is an electric circuit diagram showing an embodiment of the device of the present invention. In the figure, Q3 and Q4 are output transistors Q1 and Q2 are NPN transistors that drive them. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1 An NPN-type output transistor for power amplification, an N-type collector region, a P-type base region, and an N-type emitter region having a higher impurity concentration than the N-type collector region, the collector of which is connected to the base of the output transistor. An NP whose emitter is connected to a power supply and an input signal current applied to the base region flows through the collector region to the base region of the output transistor to drive the output transistor.
A power amplifier comprising an N-type drive transistor.