JPH04369125A - Transmission output monitor circuit - Google Patents

Abstract

PURPOSE:To obtain a monitor output with a level able to be sufficiently detected even when a transmission output is small in the case of a changing transmission output especially with respect to the transmission output monitor circuit used for a transmission section for a radio equipment or the like. CONSTITUTION:An output signal (a) of a transmitter 1 is branched into two, the one is used for a transmission output signal (b) and the other is used for an input to a high frequency switch 2 whose ON/OFF ratio is a definite value, and when the transmission output signal (b) is large, the high frequency switch 2 is turned off and when the transmission output signal (b) is small, the high frequency switch 2 is turned on, then the monitor output signal (c) reaches a sufficiently detected level.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission output monitor circuit used in a transmitting section of a radio device such as a car telephone.

0002

2. Description of the Related Art An example of a conventional transmission output monitor circuit will be described below with reference to the drawings. (FIG. 3) shows a block diagram of a conventional transmission output monitor circuit, in which 31 is a transmission device that generates a transmission signal, 32 is a directional coupler, 33 is a transmission output terminal, 34 is a monitor output terminal, and 3a is a Transmitter output signal, 3b is transmission output signal, 3c
is the monitor output signal.

In the conventional transmission output monitor circuit configured as described above, the transmitting device output signal 3a output from the transmitting device 31 is input to the directional coupler 32, and is transmitted through the directional coupler 32. The transmission output signal 3b is outputted to the transmission output terminal 33, and a part of the signal is outputted to the monitor output terminal 34 as a monitor output signal 3c.

0004

[Problem to be Solved by the Invention] However, with the above configuration, when the output of the transmission output signal is lowered, the monitor transmission output signal becomes a weak signal, so the monitor output signal cannot be detected sufficiently. There was a problem.

In view of this, the present invention uses a high frequency switch to configure a transmission output monitor circuit, thereby making it possible to extract a monitor output signal that can be sufficiently detected even when the output of the transmission output signal is lowered. The purpose of this invention is to provide a transmission output monitor circuit.

[0006]

[Means for Solving the Problems] In order to achieve this object, the present invention branches the output of a transmission output device into two, one of which is used as a transmission output, and the other with an ON/OFF ratio of a finite value and an OFF output. Sometimes, the input impedance is input to a high frequency switch close to infinity, the output of the high frequency switch is used as a monitor output, and when the transmission output is large, the high frequency switch is turned off, and when the transmission output is small, the high frequency switch is turned on. Use configuration.

[0007]

[Operation] With the above-described configuration, the present invention makes it possible to extract a monitor output signal that is sufficiently detectable even when the output of the transmission output signal is lowered.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a transmission output monitor circuit in a first embodiment of the present invention. In (Fig. 1), 1 is a transmitter that generates a transmission signal, 2 is a high-frequency switch whose ON/OFF ratio is a finite value, and whose input impedance is nearly infinite when it is OFF, and 3
is a transmission output terminal, 4 is a monitor output terminal, a is a transmitter output signal, b is a transmission output signal, and c is a monitor output signal.

The operation of the transmission output monitor circuit of the first embodiment configured as described above will be explained below.

The transmitting device output signal a outputted from the transmitting device 1 is branched into two, one becomes the transmitting output signal b at the transmitting output terminal 3, and the other becomes the input to the high frequency switch 2 and passes through the high frequency switch 2. The monitor output signal becomes C,
It is output from the monitor output terminal 4. Now, the operation will be explained using examples where the ON/OFF ratio of the high frequency switch 2 is 20 dB and the output of the transmission output signal b is 1 W and 0.01 W. When the output of the transmission output signal b is set to 1 W, the high frequency switch 2 is turned off. At this time, since the input impedance of the high frequency switch 2 is close to infinity, there is no effect on the load impedance to the transmitting device, and the transmitting device output signal a becomes almost the transmitted output signal b. On the other hand, since the high frequency switch 2 has an ON/OFF ratio of 20 dB, a small portion (approximately 0.01 W) of the transmitter output signal a appears in the high frequency switch output and becomes the monitor output signal c.

[0012] Also, the output of the transmission output signal b is set to 0.01W.
When doing so, the high frequency switch 2 is turned on. At this time,
The output of the transmitting device output signal a is divided into approximately two parts, and approximately the same output (approximately 0.01 W) as the transmitting output signal b appears as the monitor output signal c.

As described above, according to this embodiment, the output of the monitor output signal c becomes a substantially constant value that can be detected sufficiently regardless of the magnitude of the transmission output signal b, and a transmission output monitor with few errors can be realized.

FIG. 2 is a block diagram of a transmission output monitor circuit in a second embodiment of the present invention. In addition, (Figure 2
), the same or equivalent devices, signals, etc. in (FIG. 1) are designated by the same reference numerals as in (FIG. 1), and redundant explanation will be omitted. In FIG. 2, 5 is an isolator installed in front of the transmission output terminal 3.

The operation of the transmission output monitor circuit of the second embodiment configured as described above will be explained below.

By inserting the isolator 5 in front of the transmission output terminal 3, impedance fluctuations appearing at the transmission output terminal 3 when the high frequency switch 2 is ON can be suppressed. Furthermore, since reflected output due to impedance mismatch with an external device at the transmission output terminal 3 can be prevented from appearing in the monitor output signal c, the transmission output signal b can be detected with higher accuracy.

[0017]

[Effects of the Invention] As described above, the present invention enables sufficient detection regardless of the magnitude of the transmission output by configuring a transmission output monitor circuit using a high frequency switch whose ON/OFF ratio is a finite value. A substantially constant output monitor signal can be extracted, improving output monitor errors caused by the magnitude of the transmitted output.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a transmission output monitor circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a transmission output monitor circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a conventional transmission output monitor circuit.

[Explanation of symbols]

1,31 Transmitting device 2 High frequency switch 3, 33 Transmission output terminal 4, 34 Monitor output terminal 32 Directional coupler 5 Isolator a, 3a Transmitter output signal b, 3b Transmission output signal c, 3c Monitor output signal

Claims (2)

[Claims] Claim 1: The output of the transmitting device is branched into two, one is used as the transmission output, and the other is used as the input of a high-frequency switch whose ON/OFF ratio is a finite value and whose input impedance is close to infinite when it is OFF, and the above-mentioned high-frequency A transmission output monitor circuit characterized in that the output of the switch is used as a monitor output, and when the transmission output is large, the high frequency switch is turned off, and when the transmission output is small, the high frequency switch is turned on. 2. The transmission output monitor circuit according to claim 1, wherein the transmission output is output from the transmission device via an isolator.