JPH05121949A - Frequency converter - Google Patents

Abstract

PURPOSE:To improve the characteristic of a transmitter by preventing spurious radiation caused by a multiple wave from a multiplier, in the frequency converter multiplying an output of an oscillator to obtain a local oscillation signal. CONSTITUTION:An output of an oscillator 2 is multiplied by (n) at an n- multiplier 3 to obtain a local oscillation signal and it is given to a mixer 7 to frequency-convert a signal from an IF input terminal 9 and the frequency converted signal is outputted from an RF output terminal 10 as the frequency converter. A 1st filter 5 employed in the frequency converter blocks an (n+1)- multiple wave or an (n-1)-multiple wave thereby preventing the waves from being directly outputted. Furthermore, a 2nd filter 4 is employed to block a (2n+1)-multiple wave or a (2n-1)-multiple wave being a caused to a neighbouring wave generated by the mixer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency converter used in a microwave band, and more particularly to a frequency converter which uses a multiplier to generate a local oscillation signal.

[0002]

2. Description of the Related Art Conventionally, in this type of frequency converter, as shown in FIG. 2, an output of an oscillator 2 is multiplied by 4 by a quadrupler 3.
This multiplied output is passed through an unnecessary wave blocking bandpass filter 5, amplified by an amplifier 6, and input to a mixer 7 of the transmitter as a local oscillation signal. In the mixer 7, the IF signal input to the IF input terminal 9 is frequency-converted using the local oscillation signal, the unnecessary wave is removed through the bandpass filter 8, and then the RF signal is output from the RF output terminal 10.

[0003]

By the way, when an unnecessary wave other than the RF signal is output from the RF output terminal 10, it becomes a transmission spurious, which causes a problem in the characteristics of the communication device. For this reason, a bandpass filter 8 is provided after the mixer 7 to remove unnecessary waves. However, since the transmitter often sets the local oscillation frequency below the transmission RF signal in order to lower the frequency of the local oscillation signal, the fifth harmonic of the output of the oscillator 2 may come near the transmission RF band. Therefore, in the worst case, it may fall within the transmission RF band.

For this reason, in the example of FIG. 2, the unnecessary wave blocking bandpass filter 5 is provided to block unnecessary waves other than the 4th harmonic, but this kind of filter blocks the 5th harmonic near the pass band. However, it is difficult to block the 9th harmonic wave far away. Therefore, when the 9th-multiplied wave enters the mixer 7 and is mixed with the local oscillation signal of the 4th-multiplied wave, the 5th-multiplied wave of the difference is generated, and this may be output as a spurious. SUMMARY OF THE INVENTION It is an object of the present invention to provide a frequency converter that improves the characteristics of a transmitter by preventing spurious waves caused by a multiplied wave separated from the multiplier.

[0005]

A frequency converter according to the present invention is a first filter for blocking an n + 1 multiplied wave or an n-1 multiplied wave when an oscillator output is multiplied by n to form a local oscillation signal. And a second filter for blocking the 2n + 1 multiplied wave or the 2n-1 multiplied wave. For example, in a frequency converter that multiplies the output of an oscillator by 4 and mixes this with a signal in a mixer as a lower side local oscillation signal to perform frequency conversion, a first filter that blocks the 5th multiplication wave and a 9th multiplication wave are used. A second filter for blocking is provided.

[0006]

According to the present invention, the n + 1 or n-1 multiplied wave in the vicinity of the n multiplied wave is blocked by the first filter, and the 2n + 1 or 2n-1 multiplied wave causing the near wave generated in the mixer is multiplied. The wave is blocked by the second filter to prevent the n-multiplied wave near wave from being output from the mixer.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block circuit diagram of an embodiment of the present invention.
The local oscillator 1 outputs an oscillator 2 and an output of the oscillator 2 to
It is composed of a 4 × 3 for multiplying, a low pass filter 4 for blocking a 9 × frequency, a bandpass filter 5 for blocking a frequency other than the 4 × frequency, and an amplifier 6. Then, the output of the local oscillator 1 is input to the mixer 7 of the transmitter, mixed with the IF signal input from the IF input terminal 9 to be frequency-converted, and passed through the bandpass filter 8 to generate an RF signal.
An output is made from the output terminal 10.

As described above, according to the present invention, the local oscillator 1 of 4
By connecting the low-pass filter 4 to the subsequent stage of the multiplier 3, the low-pass filter 4 can block the 9-fold wave included in the signal output from the 4-multiplier 3. Also, by connecting the bandpass filter 5 to the subsequent stage, it is possible to block frequency waves other than the quadruple frequency, especially quintuple wave.

As a result, the fifth harmonic wave is not input to the mixer 7, and the ninth harmonic wave is not simultaneously input. Therefore, the 5th multiplied wave from the 4th multiplier 3 is input to the mixer 7.
Is not output to the RF output terminal 10. At the same time, the 9th multiplied wave is not mixed with the 4th multiplied wave in the mixer 7, and the 5th multiplied wave of the difference is not output. As a result, it is possible to prevent the quintuple wave from the RF output terminal 10 from being output as a spurious, and to prevent the characteristic deterioration of the transmitter.

In the above embodiment, the output of the oscillator is multiplied by 4 and used as the local oscillation signal. However, in general, the output of the oscillator is multiplied by n and used as the local oscillation signal, and the n + 1 multiplied wave, Alternatively, when the n-1 multiplied wave exists in the vicinity of the transmission RF signal band, the frequency converter is provided with a filter that blocks the multiplied wave and a filter that blocks the 2n + 1 multiplied wave or the 2n-1 multiplied wave. Therefore, the same effect can be obtained.

[0011]

As described above, according to the present invention, the first filter blocks the n + 1 or n-1 multiplied wave in the vicinity of the n multiplied wave of the output from the oscillator, and the near wave generated in the mixer is suppressed. The 2n + 1 or 2n-1 multiplied wave which is the cause is blocked by the second filter, so the mixer outputs n + 1 or n.
It is possible to prevent the -1 multiplied wave from being output as it is, or to output the n + 1 or n-1 multiplied wave generated by mixing the 2n + 1 or 2n-1 multiplied wave and the n multiplied wave in the mixer. Can be prevented and spurious can be prevented to improve the characteristics of the transmitter.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an embodiment of a frequency converter of the present invention.

FIG. 2 is a block circuit diagram of an example of a conventional frequency converter.

[Explanation of symbols]

 1 Local Oscillator 2 Oscillator 3 4 Multiplier 4 Low Pass Filter (Second Filter) 5 Band Pass Filter (First Filter) 7 Mixer 9 IF Input Terminal 10 RF Output Terminal

Claims (2)

[Claims] 1. A frequency converter that multiplies the output of an oscillator by n to form a local oscillation signal, and mixes this with a signal in a mixer to perform frequency conversion.
A frequency converter comprising a first filter that blocks a 1-multiplied wave and a second filter that blocks a 2n + 1-multiplied wave or a 2n-1-multiplied wave. 2. A frequency converter that multiplies the output of an oscillator by 4 and mixes this as a lower local oscillation signal with a signal in a mixer to perform frequency conversion. A frequency converter comprising a second filter for blocking a multiplied wave.