JPH0429262B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field) The present invention relates to a transmission output control circuit for a transmitter having a high-speed transmission rise used in FM wireless communication.

(Prior Art) Usually, a transmitter is provided with an automatic transmission output control circuit to stabilize the transmission output.

Figure 4 shows an example of the configuration of the output stage of a conventional transmitter. 41 in the figure is a power amplifier with a control terminal, and the input P _1N
A coupler 42 picks up the detection output at a level proportional to the transmission output P _OUT . 43 is a rectifier which rectifies the level proportional to P _OUT and outputs an envelope proportional to P _OUT . 44 is an error amplifier that amplifies the difference voltage between the reference value and the voltage from the rectifier 43 to a required level.
Here, the reference value is a reference voltage proportional to a specified transmission output and is given in synchronization with the transmitter's on signal (TX-ON). Reference numeral 45 denotes a low frequency filter (LPF), which is inserted to stabilize the illustrated feedback system, but this characteristic may also be included in the error amplifier.

The transmission output is stabilized by the feedback circuit described above, but since such a transmission output control circuit is an automatic control circuit, a negative feedback circuit is used to provide a certain level of LowPass characteristics. Figure 5 shows the stability characteristics of this circuit using a Bode diagram.
This is the case when two are used. 51 in Figure 5 is
Characteristics of this circuit when not using LPF, 52
and 53 are the characteristics of the lag lead filter, and 54 is 5
This is the characteristic when lag lead filters 2 and 53 are connected in cascade. In characteristic 51, the loop gain becomes 0 dB or more at a lag of 180° and is unstable, but in characteristic 54, the loop gain becomes 0 dB or less at a lag of 180° and is stable.

In this way, the Bode diagram shows that the loop gain is 0 dB or more and the phase delay is 180° or more, indicating instability.

Here, the Lagretz filter will be explained. FIG. 6 shows its circuit configuration A, gain-frequency characteristics and phase delay-frequency characteristics B, and this characteristic is used in FIG.

Returning to the explanation of FIG. 4, in the negative feedback system including the LPF as described above, it takes time to rise at the time of starting transmission (ON). An example of this rise characteristic is shown in the seventh section.
Shown in the figure. In this figure, 71 is the transmitting output vs. transmitting control voltage characteristic of the power amplifier (due to non-linearity, the transmitting output is not generated unless a certain control voltage V _D is reached), and 72 is the transmitting control voltage vs. time course when transmitting is turned on during negative feedback. The time characteristic 73 is the transmission output vs. time characteristic, which indicates that the signal rises after a certain period of time has elapsed after the transmission was turned on (origin). A characteristic of 73 is sufficient for a normal wireless transmitter, but in a wireless system that aims to perform highly efficient data transmission, it is necessary to shorten the transmission rise time as much as possible to increase the amount of transmission. However, even if the cut-off frequency of the LPF is increased as a countermeasure, there is a limit due to the stability of the negative feedback system, and due to the characteristic 71 in Figure 7, no transmission output is generated until the control voltage reaches V _D. The disadvantage is that the rise cannot be made very fast.

(Specific Object of the Invention) The present invention has been made to eliminate the above-mentioned drawbacks, and an object thereof is to shorten the rise time of the transmission output without impairing the stability of the transmission output control circuit. The transmission rise time is the period from when the transmission rise signal (TX-ON signal) arrives until the transmission output reaches the specified value.
90% ( _Figure 7) (Configuration of the Invention) Figure 1 is an example of the configuration of the output stage of a transmitter embodying the present invention. The same as each of 41 to 45 in the figure, 1 is a power amplifier with a control terminal,
2 is a combiner, 3 is a rectifier, 4 is an error amplifier, 5 is a
It is LPF. Further, 6 is a waveform generator, and 7 is an adder. The feature is that 6 and 7 are added to the conventional circuit shown in FIG. 4 to shorten the transmission rise time. Note that TX-ON is a transmission start signal.

(Operation of the Invention) In FIG. 1, when the TX-ON signal arrives, the waveform generator 6 generates an arbitrary single-shot waveform that rises earlier than the rise of the transmission output before adding the waveform generator 6 and attenuates slowly. By adding this to the loop output from LPF 5 in converter 7, the control voltage from 6 is used at the time of transmission rising, and after sufficient time for rising to complete, the output is stabilized by a feedback loop. This method of forcibly starting up using the control voltage of 6 is stable because it does not utilize a feedback loop. Once the rise is completed, the response of the feedback system is deteriorated by the LPF 5, so stability is not impaired and the rise time can be increased.

FIG. 2 shows an example of a rise characteristic using a method similar to that of FIG. 7, and will be described next. 21, 22, 23 in Figure 2 are 71, 72 in Figure 7,
73 and are shown for comparison with the present invention. 24 is a control voltage forcibly applied by the waveform generating circuit 6. 25 is when automatic control is not used (when LPF5 output is cut off in Figure 1)
The transmission output characteristics are determined only by the control voltage 24. Due to the characteristics of 21, the transmitter does not start up until V _D , but it is forced to start up quickly. 22a is the control voltage of the automatic control system when the control voltage 24 is used, 2
3a is the transmission output characteristic due to the control voltage resulting from the addition of 22a and 24, but when the control voltage of 24 is forcibly applied, the automatic control system consisting of 1 to 5 and 7 in Fig. 1 is LPF5. Since it does not follow this, the transmission output quickly rises until time _t1 . t ₁
Since the control voltage 24 from the waveform generation circuit gradually decreases after passing 24, the feedback control signal 24 in the automatic control system follows as 22a, and the transmission output can be kept constant as 23a.

Next, the waveform generation circuit 6 will be explained. This circuit converts the generated waveform 24 into a digital value, writes it to the ROM memory in advance, and turns on the transmission.
There is a method of D/A conversion while sequentially reading out the signals at the time of (TX-ON), but to simplify the circuit configuration, a circuit like the one shown in FIG. 3A can also be used. In this figure, both 31 and 32 are DC amplifiers having arbitrary gains. FIG. 3B shows the on/off signal waveform 35 of the transmitter and the output waveform 36 of the waveform generating circuit of FIG. 3A. In FIG. 3, when the transmitter is on, switches 33 and 34
is connected to the TX-ON side and a DC voltage such as 35 is applied to the C ₁ R ₁ circuit, thereby generating an output voltage such as 36 in FIG. 3B. This waveform 36 is the second
It is the same as 24 in the figure. Next, when the transmitter is off, the switches 33 and 34 are switched to the TX-OFF side and grounded by this TX-OFF signal. If switch 34 were not present, a transient portion like 37 would occur when the transmission output falls, causing the transmitter to shut down early, but if a discharge circuit using this switch is provided, the output of 32 would be 3.
8, so that the fall of the transmission output is not affected by the waveform generation circuit 6. This switch depends on the purpose of the transmitter, so it may not be used.

(Effects of the Invention) By using the transmission output control circuit of the present invention, it is possible to shorten the transmission rise time in a car telephone or the like which is intended to perform highly efficient data transmission, and thus the transmission efficiency is greatly improved. The present invention is extremely effective when a control channel of a car telephone or the like performs data transmission with a mobile object within a short period of time, and moreover, when one control channel has a large number of mobile objects to be accommodated.

[Brief explanation of drawings]

Fig. 1 is an example of the configuration of the output stage of a transmitter embodying the present invention, Fig. 2 is an example of the transmission output rise characteristic when the transmission control circuit of Fig. 1 is used, and Fig. 3 is the same as in Fig. 1. Configuration example diagram A and waveform example diagram B of the waveform generation circuit path of
Figure 4 is an example of the configuration of the output stage of a conventional transmitter;
The figure shows the Bode diagram of the stability characteristics of the circuit in Figure 4, and the Bode diagram of the stability characteristics of the circuit in Figure 6.
The figure shows the circuit configuration A of the lag lead filter used in Figure 4, and the frequency vs. gain and phase delay characteristic diagram B. Figure 7 is the transmission output rise characteristic diagram similar to Figure 2 for Figure 4. . 1, 41... Power amplifier, 2, 42... Combiner, 3, 43... Rectifier, 4, 44... Error amplifier, 5, 45... LPF, 6... Waveform generation circuit,
7... Adder, 31, 32... DC amplifier.

Claims (1)

[Claims] 1. A power amplifier having a gain control terminal, a coupler that detects a voltage proportional to the transmission output sent out from the power amplifier, and a voltage detected by the coupler that is rectified to a predetermined transmission output. an error amplifier that amplifies a voltage difference from a corresponding reference value; and a low-pass filter that smooths the output of the error amplifier and provides a control voltage to the gain control terminal of a power amplifier; In the transmission output control circuit configured such that the transmission output is stabilized by the control voltage such that the control voltage becomes zero, the low-pass filter is activated in synchronization with the transmission start signal in order to shorten the rise time of the transmission output. rises earlier than the output from the low-pass filter, and the combined value with the output from the low-pass filter is such that the transmitted output becomes a control voltage in a stable state and attenuates by the time the output from the low-pass filter reaches a steady state value. a waveform generator that outputs a single waveform voltage; and a waveform generator that is inserted and connected between the low-pass filter and the gain control terminal of the power amplifier, and that outputs the output from the low-pass filter and the output from the waveform generator. 1. A transmission output control circuit comprising: an adder for adding up and applying the result to the gain control terminal of the power amplifier as a control voltage.