JPS6248404B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission output control circuit for a transistor amplifier, and more particularly to a transmission output control circuit for a transistor amplifier using a method of varying a supply voltage.

In radio transmitters with frequencies higher than VHF (hereinafter abbreviated as transmitters), even if the antenna impedance changes, the impedance seen from the final stage amplifier of the transmitter to the antenna side does not change, and it is important to protect the transmitter. However, it is well known that an isolator (or circulator) is used as an effective device. However, isolators are expensive, and above all, they are large for VHF band transmitters, so they are not suitable for transmitters where solid-state equipment and miniaturization are important. Therefore, in general, transmitters that require miniaturization often do not use isolators, etc. In this case, as a protection measure for the transmitter, the transmission output is controlled by some means. There are methods of controlling the input level of the final stage transistor amplifier or changing the power supply voltage of the final stage transistor amplifier by detecting part of the output, reflected power, or current of the final stage transistor.

To explain this specifically, some users may connect an antenna of an abnormal length to their wireless device, or operate it without an antenna attached, and may use an isolator or the like. In a transmitter that does not have the same load, the current in the final stage transistor increases or decreases as the load changes. Furthermore, depending on the phase angle of the load, the current in the transistor increases, exceeding the transistor's ASO (safe operating area) and causing destruction of the transistor. Also
An increase in current consumption, even if it does not exceed the ASO, leads to a reduction in the operating time of a wireless device that uses battery power. For wireless devices that do not use isolators and are designed to save power,
In order to protect the final stage transistor against such a case, a method has generally been adopted in which the input level of the final stage transistor is reduced in response to the tendency of the current in the final stage transistor to increase. Although this method requires relatively little control current, if the antenna impedance fluctuates considerably, reducing the input level tends to increase the loop gain through the stray feedback circuit attached to the amplifier and cause oscillation. Therefore, it must be said that this is an unsatisfactory measure for stabilizing the final stage transistor amplifier. Compared to this, it is effective to reduce the supply voltage of the final stage transistor amplifier in response to an increase in the collector current of the final stage transistor, but as shown in Figure 1, the supply voltage of the transistor Q ₀ of the final stage amplifier is If you simply adjust the voltage between the collector and emitter of control transistor Q1 using the control voltage of control terminal ₁ , the base current of control transistor _Q1 (requires about 1/10 of the collector current) is wasted. The disadvantage was that it was consumed by resistance. In addition, as a method to reduce the base current of the control transistor,
There is also a method of connecting transistors in two stages (or more stages) as shown in Figures 2 and 3, but when the supply voltage control transistor Q ₂ or Q ₃ is in a conductive state, Q _2a or Q _3b in the figure A voltage of about 0.8 to 1V remains as the collector-emitter voltage of
The residual voltage is about 0.5 to 0.7 V larger than the collector-emitter voltage of _Q1 in FIG. This value cannot be ignored in recent low-voltage wireless devices (for example, power supply voltage of 7 to 9 V). Furthermore, in order to secure the required transmission output, the design must increase the current in proportion to the decrease in the supply voltage. Therefore, as it stands, it must be said that this is a security measure that has drawbacks for power-saving wireless devices.

An object of the present invention is to eliminate the drawbacks of the prior art as described above, and to provide a compact transmission output control circuit that can operate stably even with load fluctuations without increasing current consumption. do.

To achieve this objective, the transmission output control circuit of the present invention utilizes a method of varying the supply voltage of a transistor amplifier.
The transmission output control circuit uses the base current of the high-power first control transistor as a supply current of a transistor amplifier in the preceding stage of the transistor amplifier, and when the supply current of the first control transistor decreases, The present invention is characterized in that it is configured to include a second control transistor whose conduction is controlled by a control signal so as to replenish and supply the supply current of the previous stage transistor.

The present invention will be explained in detail below.

FIG. 4 is a circuit diagram of an embodiment of the present invention. Normally, the gain of the final stage transistor amplifier of a wireless transmitter is about 10 dB, and assuming that the efficiency of the excitation stage transistor Q ₅ in the figure is also about the same as the efficiency of the final stage transistor Q ₀ , the collector current of Q ₅ is 1/1 of ₀
It is about 0. In addition, a high-power transistor is used as the transistor _Q1 for controlling the supply voltage of the final stage transistor _Q0 , which is stable against temperature changes, has little variation in characteristics, and is close to a fully conductive state (V
h _fe (current amplification factor) so that _CE ≒ O) is obtained.
Usually around 10 are selected. The collector current (DC value) of Q ₀ is equal to the collector current of Q ₁ , and the base current of Q ₁ can be made the collector current of Q ₅ . In other words, if the collector current of Q ₀ is detected by a small resistor R ₁ and it does not reach the preset overcurrent value, that is, the specified current, Q ₄ is in a non-conducting state, and Q ₁ is almost in a fully conducting state. Therefore, the base current of _Q1 becomes the collector current (DC value) of _Q5 . When the collector current of Q ₀ exceeds the specified current, this is detected by the overcurrent detection circuit 5, and Q ₄ becomes conductive accordingly.
The base current of Q ₁ decreases, and therefore the collector current of Q ₁ decreases, increasing the collector-emitter voltage of Q ₁ and lowering the supply voltage to the final stage transistor Q ₀ . On the other hand, the collector current of the excitation stage transistor _Q5 is the sum of the collector current of _Q4 and the base current of _Q1 . The base current of Q ₁ is extremely reduced.
Even when Q ₁ is close to an open state, the collector current of Q ₅ will be supplied by the collector current of transistor Q ₄ . By the way, the base current that controls transistor _Q4 is small and can be ignored, and the relatively large base current of _Q1 complements the collector current of _Q4 and becomes the collector current of _Q5 .
Q ₁ 's control current can always be used effectively and without waste. Note that the overcurrent detection circuit 5 in FIG. 4 is provided with a setting tool VR for setting a specified current value, but since these circuits can be easily configured using well-known techniques, their explanation will be omitted. do.

As is clear from the above description, by implementing the present invention, it is possible to realize a transmission output control circuit that is stable even with load fluctuations without increasing current consumption, and it is possible to downsize the wireless transmitter. This also has a significant effect on lowering prices.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional transmission output control circuit, FIGS. 2 and 3 are connection example diagrams for reducing the control current according to the conventional technology, and FIG. 4 is a circuit configuration according to the present invention. This is an example diagram. 1... Power supply, 2... Control terminal, 3... Base terminal of final stage transistor, 4... Antenna connection terminal, 5... Overcurrent detection circuit, 6... Base terminal of excitation stage transistor, Q ₀ ... Final stage transistor, Q ₁ , Q ₂ , Q ₃ ... Supply voltage control transistor, Q ₄ ... Control transistor, Q ₅ ... Excitation stage transistor, R ₁ ... Collector current detection resistor, R ₂ ... Low-pass filter resistor, C ₁ , C ₂ ... bypass capacitor, MC ... antenna matching circuit,
MC ₀ ... Matching circuit for final stage input.

Claims (1)

[Claims] 1. In a transmission output control circuit using a method of changing the supply voltage of a transistor amplifier, the transmission output control circuit uses the base current of a high-power first control transistor as the supply current of a transistor amplifier in the preceding stage of the transistor amplifier. and a second control transistor whose conduction is controlled by a control signal so as to replenish the supply current of the preceding stage transistor when the supply current of the first control transistor decreases. A transmission output control circuit characterized by: