JP2855652B2 - Transmission device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a transmission device, and more particularly, to a transmission device of a digital wireless communication system.

[Conventional technology]

Conventionally, as shown in FIG. 4, a transmitter of this type converts a modulated signal of an intermediate frequency band inputted from a terminal 1 into a carrier of an RF band from a local oscillator 3 by a frequency converter (hereinafter referred to as MIX) 2. After passing through only the signal to be transmitted by the band-pass filter (hereinafter referred to as BPF) 4 and attenuating the unnecessary wave (carrier and the signal that has appeared on the opposite side), the output level Is amplified to the specified output level by the amplifier 5 which is automatically level-controlled so as to be constant.

[Problems to be solved by the invention]

In the above-described conventional transmission device, when there is no input to the amplifier 5, the automatic level control function of the amplifier 5 controls the amplifier 5 to the state of the maximum gain. It has the disadvantage of interfering with other communications.

When a signal is input from the terminal 1, the output of the amplifier 5 at the time of the input becomes an output of a specified level or more due to the transient response characteristic of the automatic level control function (see FIG. 5). There is a drawback that the other communication adjacent to the communication is obstructed by the spread of the communication.

[Means for solving the problem]

The transmission device of the present invention controls a frequency converter that converts an intermediate frequency signal input from a modulator to a high frequency band, a local oscillator, and a control signal that controls a level of a carrier wave input from the local oscillator to the frequency converter. A variable attenuator to be changed, an automatic level control amplifier for amplifying a required signal in a high frequency band output from the frequency converter to a predetermined output level, and a detector for detecting an input signal from the modulator. A comparator for determining whether or not a signal is input from the modulator at the output of the detector, and the comparator for gradually changing the attenuation of the variable attenuator by an input voltage from the comparator. A time constant circuit for outputting a control signal.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention, and FIGS.
(F) is a diagram showing a change in voltage or level at points A to F in FIG.

When the terminal 1 has no input, the detection voltage of the detector 6 is low,
Accordingly, a comparator (hereinafter referred to as COMP) 7 and a variable attenuator (hereinafter referred to as VAR ATT) 9 output through a time constant circuit 8.
Since the control voltage to the VAR ATT 9 decreases and the attenuation of the VAR ATT 9 increases, the output of the local oscillator 3 is attenuated and input to the MIX 2. The level including the level can be suppressed as compared with the conventional transmitting apparatus, and as a result, the output level of the amplifier 5 can also be lowered.

When a signal is input to the terminal 1 (FIG. 2 (a)), the detection voltage of the tester 6 increases, and the output voltage of the COMP 7 (FIG. 2 (b)) passes through the time constant circuit 8, Since the output voltage of the time constant circuit 8, that is, the control voltage to the VARATT 9 is gradually applied as shown in FIG. 2C, the attenuator of the VAR ATT 9 gradually decreases. Accordingly, the input level of the carrier from the local oscillator 3 to MIX2 gradually increases (second
(D), the input level of the amplifier 5 gradually increases as shown in FIG. 2 (e). Since the time constant of the automatic level control function of the amplifier 5 is faster than the time constant of the increase, the output level of the amplifier 5 does not exceed the specified output level and reaches a steady state as shown in FIG. Reach. In addition, amplifier 5
Changes as shown in FIG.

〔The invention's effect〕

As described above, the present invention detects an input of an intermediate frequency signal to a frequency converter with a detector, and in the case of no input, attenuates a carrier input from a local oscillator to a frequency converter, thereby automatically controlling an automatic level control amplifier. By suppressing the input level of, the interference to other communication paths due to carrier leak at the time of no input is suppressed, and when a signal is input, the local oscillator output level input to the frequency converter is gradually increased. By doing so, there is an effect that the output level of the automatic level control amplifier is suppressed to the current output level, the spread of the spectrum due to distortion is suppressed, and no interference is caused on other adjacent communication paths.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
To (f) show changes in voltage or level at points A to F in FIG. 1, FIG. 3 shows changes in gain of the amplifier 5 in FIG. 1, and FIG. FIG. 5 is a block diagram showing an example, and FIG. 5 is a diagram showing a change in the output level of the amplifier 5 in FIG. 1 ... input terminal, 2 ... frequency converter (MIX), 3 ...
Local oscillator, 4 ... Band pass filter (BPF),
5 ... Amplifier, 6 ... Detector, 7 ... Comparator (COMP),
8: time constant circuit, 9: variable attenuator (VAR ATT).

Claims (1)

(57) [Claims] 1. A frequency converter for converting an intermediate frequency signal input from a modulator into a high frequency band, a local oscillator, and a level of a carrier wave input from the local oscillator to the frequency converter is controlled by a control signal. A variable attenuator that changes, an automatic level control amplifier that amplifies a required signal in a high frequency band output by the frequency converter to a predetermined output level, and a detector that detects an input signal from the modulator,
A comparator for determining whether or not a signal is input from the modulator based on an output of the detector; and a control for gradually changing an attenuation amount of the variable attenuator according to an input voltage from the comparator. A transmission device comprising a time constant circuit for outputting a signal.