JPS5910008A - Power amplifier - Google Patents

Abstract

PURPOSE:To suppress the variation of a bias current due to the fluctuation of collector loss of an output transistor (TR), by providing a means to calculate the collector loss of the output TR from an output signal and a means to control the bias voltage of an output stage in response to the collector loss. CONSTITUTION:When output TRs Q1 and Q2 have a change of their collector losses, the difference between vias voltage V1 needed to the output TR and vias voltage V2 applied by a bias TRQ3 is set as V(Pc)=V1-V2=K.theta(Pc max.-Pc). In this case, Pc shows the collector loss of the output TR, and K is a constant. As a result, an output is converted into the collector loss Pc at a collector loss calculating circuit 6. Then a bias voltage control circuit 7 supplies V(Pc) on the basis of the loss Pc. Thus, the variation of a bias current due to the collector loss of the TRs Q1 and Q2 is prevented.

Description

[Detailed description of the invention] Industrial application field
This invention relates to a power amplifier equipped with an output stage (hereinafter abbreviated as 5EPP).

Conventional configuration and its problems Figure 1 shows an example of a conventional 5EPP circuit, where Ql and Q2 are output trannostars, Q:3 is a bias transistor, R1, J: R2fd bias setting. It is a resistor. Terminal 1.2 is connected to the driver stage and terminals 3, 4 to the power supply.

Terminal 5 is an output terminal.

In the conventional example configured in this way, suppose that the bias transistor Q 3 and the output transistor 7 nostar Ql, Q2
Assuming that the monitoring characteristics of Vbc - Ic are exactly the same,
For changes in ambient temperature, no change in current occurs. However, if the output signal changes and the collector losses of the output transistors Ql and Q2 change,
The output trannostars Ql and Q2 and the bias transistor Q; 3 and 3 are thermally coupled, but since there is always a thermal resistance of 1fL between them, the temperature difference between the two sides changes, and therefore, Guiasumi MR, There was a problem that the .

Purpose of the Invention Therefore, the present invention provides means for calculating the collector loss of the output 1·, /7 nostar from the output signal, and means for adjusting the bias voltage of the output stage according to the collector loss of the The present invention provides a power amplifier that suppresses variations in bias current due to variations in collector loss.

DESCRIPTION OF THE EMBODIMENT FIG. 2 shows an embodiment of the present invention. The same reference numerals as in FIG. Then, the output transistor Ql
, a circuit for calculating the collector loss of Q2, and 7 a circuit for adjusting the bias voltage according to the collector loss.

Let Vl be the bias voltage required to flow the optimum bias current to the output trannostars Ql and Q2, then Vl is determined by the output transistor's junction quality TI, as follows: Vl==VLa-(TL-'ra) ・K Again,
When the Via/noyanction temperature is Ta, the required bias voltage, Kl constant, changes as expressed by:

Similarly, the voltage between the collector and emitter of the via transistor Q3 is V2a-(T2-Ta) in V2.
2. Collector-to-emitter die pressure when the junction temperature is 'r2, V2a Collector-to-emitter die pressure when the junction temperature is Ta, Kl/constant, The collector loss of the output transistor is at its maximum. When the output transistor and the bias transistor Q3 are different from each other (the quality is T l', T
2', T l' - T 2' = Pc max, -θ output,
pc rTlaX, - Maximum peak of the collector loss of the output transistor, θ... Heat from the output transistor to the bias transistor 4'' (resistance (℃/W)), and now the bias voltage given by the bias transistor Q3 To be the maximum bias voltage required for the output transistors Ql and Q2, Vl'2v2' However, ■1' When the temperature of the output transistor is Tl', the required bias voltage, V2'... V2a can be set so that the voltage between the collector and emitter of Q3 when the junction temperature of transistor Q3 is T 2', so Kl=2
2, then V2a = V l a - K ・ (Tl'-
R1 is not adjusted so that T2')==V J a- to -Pc max, θ. Bye.

If the collector losses of the output transistors Ql and Q2 change in this state, the required
The difference V (pc) between the bias voltage V1 and the bias voltage ■2 given by the bias transistor Q:
・The collector loss of the output trannostar is as follows.

From the above, the output is converted to the collector loss Pc in the collector loss circuit 6, and the bias voltage adjustment circuit 7 changes V(pc) based on this pc, so that the collector loss of the output transistors Ql and Q2 is It is possible to prevent fluctuations in the Guiasmi flow due to IJ.

Effects of the Invention As explained in Section 2, according to the present invention, it can withstand constant changes in the surroundings, bubbles in the output transistor, and excessive heat generation.・It is possible to provide a power amplifier in which a constant ζ-iasumi current is always supplied.

[Brief explanation of drawings]

- Figure 1 is a diagram of a conventional 5EPP circuit, and Figure 2 is a circuit configuration diagram of an embodiment of the present invention. Q, l, Q2... Output transistor, Q3 Bias river I/Lannostar, R, l, R,2... Bias setting resistor, 6 - Circuit that calculates the collector loss of the output transistor from the output signal, 7 Collector loss A circuit that adjusts the bias voltage according to the Figure 1 1 3 2 4 Figure 2 3

Claims (1)

[Claims] In a power amplifier having a single-ended output stage, there is a means for calculating the collector loss of the output transformer by detecting the entire output voltage or current, and a means for calculating the collector loss of the output transformer by detecting the entire output voltage or current, and a means for calculating the collector loss of the output transformer according to the calculated collector loss.
and means for adjusting the bias voltage of the pushpull output stage to compensate for the bias current of the single-ended pushpull output stage due to self-heating of the output transnoster. power amplifier.