JPS63242008A - Highly efficient class b amplifier - Google Patents

Abstract

PURPOSE:To obtain a highly efficient amplifier by detecting a current flowing through active components arranged in series without connecting a load to one of plural output circuits whose inputs are connected in parallel and using the information so as to control the input of the output circuits thereby applying negative feedback relating to the increase/decrease in the through-current. CONSTITUTION:An identical circuit to an output circuit 2 is provided as a dummy output circuit 3. The circuit consists of transistors(TRs) 11, 12, the gate and source being the inputs are connected in parallel with the output circuit 2 and the circuit is operated simultaneously. Since no load is connected to the dummy output circuit 3, only a through-current iA2 flows to the TRs 11, 12. The current iA2 is proportional to the area ratio of the TR 11 and a TR 209 and the area ratio of the TR 12 and a TR 308. When the area ratio is the unity, the relation of iA1=iA2 exists and the iA1 is extracted indirectly by detecting the current iA2.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an amplifier, and in particular, to a high efficiency amplifier suitable for applications requiring low power consumption. [Prior Art] A conventional amplifier is For example, as described in Japanese Unexamined Patent Publication No. 55-166515, two transistors constituting the output stage 8 have a combination in which one has a low and constant output current capability, and the other has a sufficiently high capability. I was using things.

On the other hand, it is also known that both transistors are modified to have sufficiently high performance to improve their dynamic characteristics.

[Problem that the invention seeks to solve]

However, regarding the stabilization of the idle link current (current flowing through two output transistors, hereinafter referred to as through current), which is one of the static percentage characteristics that is an important parameter of a four-width amplifier, the output ' It is necessary that an element with a low and constant hjL current capability be present in either of the two transistors configured in series, which contributes to stabilization.

If both of these are changed to ones with sufficiently high performance, if the bias is biased toward the conduction direction of the output transistor due to variations in the circuit elements, a large amount of through current will flow in the direction of shorting the power supply.

The above conventional technology does not take into account stabilization control for the through current, and the through current fluctuates greatly due to variations in elements during circuit manufacturing and changes in operating temperature, resulting in poor yield. However, there is a problem in that there is a significant decrease in the amount of water used, and that the conditions of use must be restricted.

The necessity of stabilizing the flow through '4 will be discussed below.

Power amplifiers that require low power consumption generally choose a class 3 bush-pull configuration. In the operation of the third-class bush pull, the positive side of the output amplitude is amplified by one transistor, and the negative side of the output amplitude is amplified by the other transistor. Therefore,
The characteristics of the output transistor are required to have sufficiently high output current capability and to be uniform on the positive side and the a side.

Next, the output waveforms on the positive side and the negative side are slightly overlapped so that they are well connected, and a section is provided in which both are amplified.

In this M section, there is a through current flowing through both transistors.

This negative current is the M'H point of the present invention, and if this current is not small, the continuity of the positive and negative waveforms will be lost.
So-called crossover distortion occurs and degrades the performance of the amplifier. Moreover, if this through current is too large, it heats up the output transistor 8 and does not provide any output, resulting in wasted power. In severe cases, the power dissipation of the output transistor may be exceeded, leading to destruction.

An object of the present invention is to realize a highly efficient amplifier by stabilizing the through current and always maintaining the necessary minimum amount.

[Means for solving problems]

In order to achieve the above object, in the present invention, another pseudo output circuit is provided in the output circuit of the amplifier, and the input thereof is connected in parallel with the input of the output circuit. No load is connected to this pseudo output circuit, and a current detection circuit is connected in series between the two output transistors. By operating these at the same time, the through current equivalent to the output circuit is obtained from the current detection circuit connected to the pseudo output circuit, which is returned to the differential amplifier stage and mixed to suppress the output of the differential amplifier stage. By controlling the output circuit so that the through current is reduced, a negative feedback loop is activated and the operation of the output stage is stabilized. As a result, the minimum required through-current is always maintained, and a highly efficient amplifier can be achieved.

[Effect]

In each output transistor, the through current and the output current are superimposed and cannot be separated, so the through current cannot be directly detected.

The key point of the present invention lies in the technology for separating and extracting the through current.

In this method, another set of circuits identical to the output circuit is created as a pseudo output stage, and the output stage and input are connected in parallel and operated simultaneously. Also, do not connect a load to the pseudo output circuit.

By doing this, the current flowing through the transistors arranged in series in the pseudo output circuit is equal to the through current that separates the output current from the output circuit current.Next, the pseudo output circuit is Configure with rent mirror. A current mirror has the effect that the current ratio becomes n by configuring the areas of two transistors operated in parallel to have a constant ratio (n). Since the pseudo output circuit does not take an output, it can be small, for example, n = 1. A current detection circuit is placed in the flow path that passes through the transistors arranged in series in the pseudo output circuit, and accurately detects the through current. Detect.

The shoot-through current is converted into a floating 'wIJ current source that is easy to interface with the differential amplifier stage in the current sensing circuit.

When the through current increases, the output of the 1st current detection circuit increases, the output of the differential amplifier stage is weakened, the gate voltage of the output circuit decreases, and the output circuit C/JX conduction current decreases (negative feedback). acts. This stabilizes the negative current, so
There is no deterioration in amplifier performance or increase in power consumption.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to FIG. 1. In FIG. 1, 1 is a differential amplification stage, 2 is an output circuit,
This is done using the above-mentioned known technology. 3 is a pseudo output circuit, 4 is a current detection circuit, and 3 and 4 are newly created circuits according to the present invention. 2 output circuit is transistor 2
09 and 308 are connected in series between the power supplies. The midpoint is used as the output and power is supplied to the load. Further, the transistor 209 is driven by the transistor 207 of the differential amplifier stage 1, and is given sufficient excitation to be deeply conductive.
Moreover, the output 'eL current capability of the transistor 209 is sufficiently high. Further, the transistor 608 is driven by the transistor 607 of the differential amplifier stage 1, and similarly, its output current capability is sufficiently high, and its characteristics are well balanced with the transistor 207.3. Output The transistor 209 receives the positive side of the current,
Transistor 308 takes charge of the negative side. Current flows in both switching sections, maintaining output continuity.

The flow path through which current flows in both is a through current flowing from transistor 209 to transistor 308, which is indicated by iA. Each output transistor has iA and an output current i.
Since L1 or iLz is superimposed, it is not possible to directly detect only iA.

Therefore, the present invention provides another circuit that is the same as the output circuit 2,
It is provided as a pseudo output circuit 5. This is transistor 1
1 and 12, and its input gate and source are connected in parallel with the output circuit 2 and operate simultaneously. Since no load is connected to the pseudo output circuit 6, only the through current iA2 flows through the transistors 11 and 12.

This iA2 is proportional to the area ratio of transistor 11 to transistor 209 and the area ratio of transistor 12 to transistor 308. If the area ratio is 1, iA! = iA
z, and by detecting iAz, iAx is indirectly extracted. In the current detection circuit 4, the output impedance of the power ξ transistors 11 and 12 present in the iAz flow path is sufficiently high, so the change in iAz due to the insertion of the current detection circuit 4 can be ignored.

The purpose of the current detection circuit 4 is to provide an interface for easily mixing the detected current information to the differential amplifier stage.
The operation is as follows. Transistors 13 and 15 and transistors 14 and 16 form current mirrors, and have a current conversion ratio according to their area ratios. Using the high output impedance of the drain terminals of the transistors 15 and 16, a constant current source that is not affected by the impedance of the connected device is converted. By connecting this information to the gates of output transistors 207 and 307 of the differential amplifier stage, a negative feedback current loop is formed. ) Run raster 11. Transistor 14. A loop is formed through transistor 16 and back to transistor 207.

Furthermore, transistor 307. Transistor 12. )? 13. Transistor 15 through transistor 30
Form a loop back to 7. The operation is as follows: if iAz increases, the gate-source voltage of transistor 14 increases, the drain current of transistor 16 increases, the gate-source voltage of transistor 207 increases, and the drain of transistor 207 increases. -The source voltage decreases, the gate-source voltage of transistor 11 decreases, and the drain current of transistor 11 decreases, so
iA2 decreases.

In other words, it has a negative feedback effect and has a function of stabilizing iA2. Also, another loop passing through transistor 307 operates in the same manner. If iAz becomes stable, iAl will also become stable.

The effect of negative feedback according to the present invention is greater than the stabilization of iAs (
The second figure shows that it is effective. Figure 2 shows the variation of iAl with respect to variations in the gate width of the transistor 207.The operation is as follows: if the gate width of the transistor 207 is narrow, the drain current of the transistor decreases and the drain voltage increases as shown in Figure 1. As a result, the gate-source voltage of transistor 209 increases and its drain 'IiE current increases, so that iAl increases. Similarly, iAz also increases. Figure 2 shows that if the gate width of the transistor 207 is reduced by 5 inches, the iAr
increases by about 40 times, and remains at 1.6 times when the negative feedback effect according to the present invention is used.

The present invention has the effect of stably suppressing the through current, which is important in static characteristics, and is an effective means for an amplifier with low St power consumption. Furthermore, the present invention can be applied to all types of amplifiers that take output from a connection point between active elements arranged in series between 1ilr and 1100 nm, and have great industrial utility value.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize a highly efficient amplifier with stable through current.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a current iA+ corresponding to variations in the gate width of the transistor 207.
FIG. 1... Differential amplifier stage 2... Output circuit 3... Pseudo output circuit 4... Current detection circuits 11 to 16...
Transistors 207, 507, 209, 308...Transistors Output recitation 3 pseudo output humiliation

Claims (1)

[Claims] 1. In an amplifier that takes an output from a connection point between active elements arranged in series between power supplies, a plurality of output circuits with inputs connected in parallel are provided, and at least one of these output circuits is connected without a load. Detects the current flowing through the active elements arranged in series, and uses that information to control the input of the output circuit,
A high-efficiency class B amplifier characterized in that negative feedback is applied to increase or decrease the through current.