JPH05175857A - Radio transmitter - Google Patents

Abstract

PURPOSE:To obtain the radio transmitter reducing distortion in the waveform of a transmitting output by adjusting the transmitting output by adjusting the level of a signal before modulation. CONSTITUTION:A high frequency signal outputted from a high frequency generating circuit 2 is inputted through a level adjusting part 4 to adjust the signal level to a mixer 1. A modulated signal outputted from a modulator 3 is inputted to the mixer 1. Frequency conversion is executed by mixing the unmodulated high frequency signal inputted through the level adjusting part 4 to the mixer 1 with the modulated signal outputted from the modulator 3. The output signal of the mixer 1 is passed through a power amplifier 5 and transmitted from a transmitting antenna 6. Thus, the transmitting output is adjusted by adjusting the signal level of the unmodulated high frequency signal. Further, a level detection part is provided in the rear step of the mixer 1 and therefore, feedback control is executed to the transmitting output so that the signal level detected by this level detection part can be coincident to a reference level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio transmitter equipped with a mixer for performing frequency conversion by mixing a high frequency signal with a modulation signal.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 5, a radio provided with a mixer 1 for performing frequency conversion by mixing a high frequency signal output from a high frequency generation circuit 2 with a modulation signal output from a modulator 3. The transmitter is known. That is, the frequency of the modulated signal is f ₁ and the frequency of the high frequency signal is f ₁ .
Assuming that the output frequency of the mixer 1 is ₂ ,
We obtain f ₁ + f ₂ . Generally, the output of the high-frequency generation circuit 2 is fixed so that the efficiency of the mixer 1 is maximized, so that the transmission output is usually adjusted after the mixer 1.

That is, the output of the mixer 1 is input to the power amplifier 5 through a level adjusting section 4'such as a variable resistor or an attenuator circuit and then added to the transmission antenna 6, or as shown in FIG. (Automatic P
The power control circuit 10 is added to keep the transmission output constant.

[0004]

In the above configuration, since the transmission output is adjusted by adjusting the level in the subsequent stage of the mixer 1, the level of the modulated signal is adjusted, and the power is adjusted. There are problems that the input waveform to the amplifier 5 is distorted and the output waveform of the power amplifier 5 is distorted.

An object of the present invention is to solve the above problems, and to provide a radio transmitter in which the transmission output is adjusted by adjusting the level of a signal before modulation, thereby reducing the distortion of the waveform of the transmission output. It is the one we are trying to provide.

[0006]

In order to achieve the above object, the invention of claim 1 is a radio transmitter equipped with a mixer for mixing a high frequency signal with a modulation signal to perform frequency conversion. That is, a level adjusting unit for adjusting the signal level of the high frequency signal is provided. According to the invention of claim 2, a level detecting section for detecting a signal level at a subsequent stage of the mixer, and a comparing section for outputting an adjusting signal according to a difference between the signal level detected by the level detecting section and a preset reference level. Based on the adjustment signal from the comparison unit, the level adjustment unit is controlled so that the signal level detected by the level detection unit matches the reference level.

[0007]

According to the first aspect of the invention, since the level adjusting section for adjusting the signal level of the high frequency signal input to the mixer is provided, the signal level of the unmodulated high frequency signal is adjusted. The output can be adjusted stably without distorting the waveform.

According to the second aspect of the present invention, the level detecting section for detecting the signal level of the latter stage of the mixer is provided and the level adjusting section is controlled so that the detected level matches the reference level. By changing it, the transmission output can be adjusted, and further, the level adjustment unit is feedback-controlled so as to keep the transmission output substantially constant, so that the transmission output is stabilized.

[0009]

(Embodiment 1) In this embodiment, as shown in FIG. 1, a high frequency signal output from a high frequency generating circuit 2 is input to a mixer 1 through a level adjusting section 4 for adjusting the signal level. Further, the modulation signal output from the modulator 3 is input to the mixer 1. Mixer 1 through level adjuster 4
The frequency conversion is performed by mixing the unmodulated high frequency signal input to the input terminal with the modulation signal output from the modulator 3. The output signal of the mixer 1 is transmitted from the transmitting antenna 6 through the power amplifier 5. In this way, the transmission output is adjusted by adjusting the signal level of the unmodulated high-frequency signal, so that the distortion that occurs when adjusting the signal level after modulation does not occur.

The level adjusting section 4 may have a structure as shown in FIGS. 2 (a) to 2 (c). Figure 2 (a)
Is a level adjusting section 4 consisting of only the variable resistor VR _1, it is to enter the high-frequency signal output from the high frequency generating circuit 2 to the mixer 1 through the variable resistor VR _1.
In FIG. 2B, a transistor Q is used and a variable resistor VR ₂ is provided in the emitter resistance of the transistor Q. The high frequency signal input to the base of the transistor Q is the set value of the variable resistor VR ₂ . The signal level is adjusted according to the above, and is input to the mixer 1 from the collector of the transistor Q. The level adjusting unit 4 of FIG. 2C has a configuration in which a variable capacitor VC whose one end is grounded is connected to a transmission path of a high frequency signal, and if the variable capacitor VC is adjusted, it is input to the mixer 1. The signal level of the high frequency signal can be adjusted.

(Embodiment 2) In the present embodiment, as shown in FIG. 3, a level detector 7 is provided in a stage subsequent to the mixer 1, and the signal level of the output signal of the power amplifier 5 is detected by the level detector. It is designed to detect at 7. Level detector 7
Can use a directional coupler or can be configured by a strip line and a detection circuit, and outputs a voltage according to the signal level of the transmission output. Further, the signal level detected by the level detection unit 7 is compared with the reference level preset in the reference level setting unit 8 by the comparison unit 9. The comparison unit 9 is configured using a differential amplifier or an operational amplifier, and outputs an adjustment signal that is a voltage signal corresponding to the level difference (voltage difference) between the signal level detected by the level detection unit 7 and the reference level, This adjustment signal is input to the level adjustment unit 4. As shown in FIG. 4, the level adjuster 4 includes a series circuit of DC cut capacitors C ₁ and C ₂ and a diode D inserted in a transmission line between the high frequency generation circuit 2 and the mixer 1, and a diode. High-frequency cutting inductors L ₁ and L ₂ are respectively connected to both ends of D, and the adjustment signal is applied via the inductor L ₁ connected to the anode of the diode D. Therefore,
Since the DC bias is applied to the diode D by the adjustment signal, the ON resistance of the diode D can be adjusted according to the voltage of the adjustment signal, and the attenuation amount of the high frequency signal can be adjusted. In this way, the level adjusting unit 4
The signal level of the high frequency signal output from the high frequency generator 2 is adjusted according to the adjustment signal. As a result, the transmission output is feedback-controlled so that the signal level detected by the level detection unit 7 matches the reference level, and the transmission output is kept substantially constant. Further, if the reference level set in the reference level setting unit 8 is adjusted, the transmission output can be adjusted. Other configurations are similar to those of the first embodiment.

[0012]

According to the first aspect of the present invention, since the level adjusting unit for adjusting the signal level of the high frequency signal input to the mixer is provided, the signal level of the unmodulated high frequency signal is adjusted. There is an advantage that the output can be adjusted stably without distorting the waveform.

According to a second aspect of the present invention, a level detecting section for detecting the signal level at the subsequent stage of the mixer is provided, and the level adjusting section is controlled so that the detected level matches the reference level. Thus, the transmission output can be adjusted, and further, the level adjustment unit is feedback-controlled so as to keep the transmission output substantially constant, so that the transmission output is stabilized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment.

2A, 2B, and 2C are circuit diagrams showing various circuit examples of a level adjusting unit used in the first embodiment.

FIG. 3 is a block diagram showing a second embodiment.

FIG. 4 is a circuit diagram of a level adjusting unit used in the second embodiment.

FIG. 5 is a block diagram showing a conventional example.

FIG. 6 is a block diagram showing another conventional example.

[Explanation of symbols]

 1 mixer 2 high frequency generating circuit 3 modulator 4 level adjusting unit 5 power amplifier 6 transmitting antenna 7 level detecting unit 8 reference level setting unit 9 comparing unit

Front page continuation (72) Inventor Kazuhiro Matsumoto 1048, Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Works Co., Ltd.

Claims (2)

[Claims] 1. A radio transmitter including a mixer for performing frequency conversion by mixing a high frequency signal with a modulation signal, wherein a level adjusting unit for adjusting a signal level of a high frequency signal input to the mixer is provided. Wireless transmitter. 2. A level detecting section for detecting a signal level in the latter stage of the mixer, and a comparing section for outputting an adjustment signal according to a difference between the signal level detected by the level detecting section and a preset reference level. 2. The radio transmitter according to claim 1, further comprising: a level adjusting unit controlled based on an adjusting signal from the comparing unit so that a signal level detected by the level detecting unit matches a reference level.