JPH0771054B2 - Transmission output control circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly used in a TDMA radio transmitter for transmission that controls the output level of a burst-like transmission wave and the rising and falling characteristics of the output over a wide dynamic range. The present invention relates to an output control circuit.

2. Description of the Related Art Conventionally, this type of transmission output control circuit has a so-called automatic power control (APC) circuit as shown in FIG. 3, and the transmission output is controlled against fluctuations in various conditions such as power supply voltage, input, and temperature. It plays a role of keeping constant. In FIG. 3, 1 is transmission
VCO, 2 is a transmission power amplifier circuit, 3 is a directional coupler, 4 is a detection circuit using a diode, and 5 is a comparison error amplifier. The output from the transmission VCO 1 is power-amplified by the transmission power amplification circuit 2 and transmitted through the directional coupler 3. The directional coupler 3 partially branches the output of the transmission power amplification circuit 2 and supplies it to the detection circuit 4, and inputs the detection output to the comparison error amplifier 5. The comparison error amplifier 5 compares the detected output with the reference waveform 8 (Vref) and applies the control voltage V _APC to the transmission power amplification circuit 2 according to the comparison result to control the amplification degree. Thus, the transmission output control negative feedback loop is configured. Since the transmission output level usually takes discrete values and the maximum and minimum level difference is 20 dB at most, a generally known simple detection circuit using a diode can almost achieve the purpose.

However, in the narrow band TDMA wireless communication which will be widely spread in the future, since the transmission wave is in a burst form, in order to suppress the spread of the spectrum to the adjacent channel, the transmission wave It is necessary to accurately control the rising and falling characteristics of.

As an example, in the GSM standard, which is the European unified standard for digital cellular phones, the rise and fall response time characteristics are defined by the output lower limit of -36 dBm or the level relative ratio to the peak value at the -70 dBc point and the -30 dBc point, and the peak value. It defines the time to reach.

However, as mentioned above, a general detection circuit is an application of the detection characteristics of a diode, so the dynamic range is essentially narrow, and even with some devise, it is only a few dozen dB, and the controllable transmission output range is Much shortage.

The present invention solves such a conventional problem, and an object thereof is to compensate for the lack of the dynamic range of the detection circuit and to control the transmission output over a wide dynamic range with good reproducibility.

Means for Solving the Problems In order to achieve the above object, the present invention provides a directional coupler that separates a part of the output of a transmission power amplifier circuit, a variable attenuator that attenuates the separated output, and this variable attenuation. And a means for controlling the amplification degree of the transmission power amplifier circuit according to the result of comparison between the output of the detector circuit and the reference value.

Operation The operation of the above configuration is as follows. A part of the transmission output output from the transmission power amplification circuit is taken out by the directional coupler, passes through the variable attenuation circuit, and is detected by the detection circuit.
When the attenuation amount in the variable attenuation circuit increases, the detected value decreases and the transmission output apparently decreases. Therefore, the negative feedback loop operates to increase the transmission output. Therefore, according to the present invention, the transmission output can be controlled with good reproducibility over a wide dynamic range by combining with the control by the variable attenuator without depending on the expansion of the dynamic range of the detection circuit.

Embodiment FIG. 1 shows the configuration of an embodiment of the present invention. In the figure, the same parts as those in FIG. A variable attenuation circuit 6 attenuates the transmission output extracted by the directional coupler 3 and supplies it to the detection circuit 4. A control line is connected to the variable attenuation circuit 6 so that an arbitrary amount of attenuation can be instantaneously obtained. The control line of the variable attenuator circuit 6 mainly controls the switching of the output level.

Taking the above GSM standard as an example, the transmission output is 43 dBm to 13 dBm.
It is divided into 16 stairs in 2dB steps. The burst waveform time mask is specified by relative values and requires control of 30 dB or more. In the case of the minimum output level, since it is controlled from 17 dBm, the control range is really 60 dB. The dynamic range necessary for controlling the burst waveform is given to the detection circuit, and the variable attenuator takes control of the transmission level with high accuracy of 2 dB steps. For this purpose, the variable attenuator configuration should be 2 ^N dB.
One means is to make a continuous connection of (N = 1,2,3,4) attenuators. This is because, if the transmission output level data is 4-bit parallel, it can be taken in by the control line as it is, so that the configuration is simple and the accuracy is high. An example of this structure is shown in FIG.
The variable attenuator circuit 6 includes a 2 dB attenuator 61, a 4 dB attenuator 62, and an 8 dB attenuator 6
It consists of 3 and 16dB attenuator 64, and 0 to 30 in 2dB steps depending on the transmission output level 4-bit data D1, D2, D3, D4.
Attenuation control is performed in 16 steps of dB. Of course, one control line may be used as an analog value, but it is necessary to consider so that the accuracy of the attenuation amount can be obtained.

The present invention has the above-mentioned configuration and enables TDMA transmission output control. More specifically, the above-mentioned output control with a dynamic range of 70 dB is divided into burst waveform control and output level control. The control of the burst waveform is to prevent the spread of the frequency spectrum.
The dynamic range of is controlled from the lower limit to the above. A detection range of 30-40 dB is usually sufficient. Therefore,
The reference waveform 8 input to the comparison error amplifier 5 is basically constant regardless of the transmission power level.

Next, since the control of the transmission power level is determined before the start of transmission, the attenuation amount of the variable attenuation circuit 6 is set according to the value. That is, the amount of attenuation is maximum at the maximum output, and in order to reduce the output by, for example, 2 dB, the amount of attenuation may be reduced by 2 dB. That is, the change width of the variable attenuation circuit 6 matches the change width of the transmission output. Generally, the variation in the attenuation characteristic is easier to manage than the variation in the detection characteristic, so that the accuracy of the output level becomes higher. As a concrete method of constructing the variable attenuation circuit, it is of course possible to arrange linear amplifiers in a mixed manner in order to improve impedance characteristics and isolation characteristics so as to improve accuracy.

As described above, according to the above-described embodiment, since the wide transmission output control range is shared by the digitally controllable variable attenuator and the highly feasible diode detection circuit, the dynamic range of the conventional detection circuit is increased. Compared with a transmission output control circuit that relies solely on this, output control with higher accuracy and reproducibility becomes possible.

As is apparent from the above embodiment, the present invention provides a high-frequency variable attenuation circuit before the detection circuit in the transmission output control circuit and controls the attenuation amount according to the transmission output level. This has the effect of enabling control of the transmission output level waveform over a very wide output level range that has not been obtained. In addition, the accuracy of setting the output level is also improved. In addition, the fact that only one rising / falling reference waveform is required for burst control is a great advantage, and it can greatly contribute to improving the productivity of equipment.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a transmission output control circuit according to the present invention, FIG. 2 is a block diagram showing the configuration of the variable attenuator in FIG. 1, and FIG. 3 is a block diagram of a conventional transmission output control circuit. Is. 1 ... Transmission VCO, 2 ... Transmission power amplification circuit, 3 ... Directional coupler, 4 ... Detection circuit, 5 ... Comparison error amplifier, 6
...... Variable attenuation circuit, 8 ... Reference waveform (Vref).

Claims (1)

[Claims] 1. A transmission power amplifier circuit for amplifying transmission power,
A directional coupler that separates a part of the output of the transmission power amplification circuit, a variable attenuator that attenuates the separated output, a detection circuit that detects the output of the variable attenuator, and an output of the detection circuit and a reference. And a means for controlling the amplification degree of the transmission power amplifier circuit according to the result of comparison with the value.