JPH01144824A - Spurious reduction circuit by intermediate frequency higher harmonic wave - Google Patents

Abstract

PURPOSE:To reduce spurious caused by IF higher harmonic wave by providing a synthesizing device synthesizing an IF signal whose phase is converted and an IF signal in a band outputted by a mixer circuit on the front stage of a band-pass filter. CONSTITUTION:An IF signal generation circuit 6 generates the same intermediate frequency signal as the spurious of the intermediate frequency existing in the band of transmission frequency. Then, an IF signal level setting circuit 7 adjusts the level of the intermediate frequency signal generated by the circuit 6 so as to be the same level of as the intermediate frequency signal existing in the band of the transmission frequency. Besides, a phase conversion circuit 8 changes the phase of the intermediate frequency signal whose level is adjusted to be the same, makes it to a reverse phase for the phase of the intermediate frequency signal existing in the band and outputs it to the synthesizing device 9. Then, the composition unit 9 synthesizes the intermediate frequency signal existing in the band of the transmission frequency outputted from the mixer circuit 1 and the intermediate frequency signal of the reverse phase outputted form the circuit 8 and cancels the intermediate frequency signal existing in the band of the transmission frequency. Thus, the spurious caused by the IF higher harmonic wave can be reduced.

Description

[Detailed Description of the Invention] [Summary] Regarding a spurious reduction circuit that reduces spurious caused by harmonics of an intermediate frequency existing within a transmission frequency band, the present invention is capable of reducing spurious caused by IF harmonics generated in a MIX circuit. The purpose of the present invention is to provide an IF signal generation circuit that generates a spurious signal that is identical to an intermediate frequency spurious that exists within the transmission frequency band of a wireless transmitter, and that sets the level of the identical spurious signal to a predetermined value. an IF signal level setting circuit for setting the set IF signal level, a phase conversion circuit for converting the set IF multiplied signal phase, and
A synthesizer for synthesizing the F-fold signal and the in-band IF signal output from the mixer circuit is provided at a stage before the band-pass filter.

[Industrial application field]

The present invention relates to a spurious reduction circuit for an FM radio transmitter,
In particular, the present invention relates to a spurious reduction circuit that reduces spurious caused by harmonics of intermediate frequencies existing within a transmission frequency band.

[Conventional technology]

FIG. 5 shows a block diagram of the main parts of a conventional radio transmitter, which mixes the intermediate frequency (IF frequency) formed in the previous stage (not shown) and the local (LO) frequency output from the local oscillator 2. Mixer circuit (M
IX) 1, a bandpass filter (BPF) 3 that blocks unnecessary frequencies present in the output signal of MIX1, and a BPF
3, and a high frequency amplifier 4 for amplifying the output signal of No. 3.

MIXI mixes the IF frequency and the LO2 oscillation frequency, takes out the difference frequency and forms the transmission frequency, and
Output to PF3. BPF3 blocks and attenuates spurious parts of the LO frequency and its harmonics, the harmonics of the transmission frequency, and the harmonics of the IF frequency output from MIXI,
The ratio of the transmission signal level to the spurious signal level is increased and outputted to the high frequency amplification section 4. High frequency amplifier 4 is BP
The transmission signal output from F3 is amplified and transmitted.

[Problem that the invention seeks to solve]

In the above FM radio, MIXI is made into a balanced type, the blocking attenuation of BPF3 is increased, and B
A new low-pass filter or the like is added to the PF3 to block and attenuate some of the spurious waves of the LO frequency and its harmonics, the harmonics of the transmission frequency, and the harmonics of the IF frequency.

However, if we pay attention to the spurious caused by the harmonics of the IF frequency, we can see that the transmission frequency is the harmonic of the IF frequency and the BPF.
If they are far enough apart to be separated by 3, it can be reduced using conventional methods, but as shown in Figure 6, there is a spurious with a frequency N times the IF frequency within the passband of BPF3 near the transmission frequency. Then it becomes impossible to attenuate.

Furthermore, when this spurious passes through the high frequency amplifier 4 having non-linearity, as shown in FIG.
There is a problem that high-quality transmission radio waves cannot be obtained.

The present invention was created in view of these points, and is based on MI
It is an object of the present invention to provide a spurious reduction circuit that can reduce spurious caused by IF harmonics generated in an X circuit.

[Means for solving problems]

FIG. 1 shows a principle block diagram of a spurious reduction circuit using IF harmonics of the present invention, in which the input intermediate frequency and the local oscillation frequency are mixed in a mixer circuit 1 to create a transmission frequency, and the frequency band of the transmission frequency is After removing the external spurious with a band pass filter (BPF) 3, in a wireless transmitter that transmits through a high frequency amplifier 4, an IF that creates a spurious signal identical to the intermediate frequency spurious that exists within the transmission frequency band. a signal generation circuit 6; an IF signal level setting circuit 7 for setting the level of the same spurious signal to a predetermined value; a phase conversion circuit 8 for converting the phase of the intermediate frequency signal whose level has been set; A synthesizer 9 for synthesizing the intermediate frequency signal and the in-band intermediate frequency signal output from the mixer circuit is provided upstream of the band pass filter 3.

[For production]

The IF signal generation circuit 6 generates an intermediate frequency signal that is the same as the intermediate frequency spurious that exists within the transmission frequency band.

Next, the IF signal level setting circuit adjusts the level of the intermediate frequency signal created by the IF signal creating circuit 6 so that it becomes the same level as the level of the intermediate frequency signal existing within the transmission frequency band.

Next, the phase conversion circuit 8 changes the phase of the intermediate frequency signal adjusted to the same level so as to have an opposite phase to the phase of the intermediate frequency signal existing within the band, and outputs it to the synthesizer 9.

The synthesizer 9 synthesizes the intermediate frequency signal existing within the transmission frequency band outputted from the mixer circuit 1 and the opposite phase intermediate frequency signal outputted from the phase conversion circuit 8 to generate an intermediate frequency signal existing within the transmission frequency band. Cancels the intermediate frequency signal, IF
Reduces spurious caused by harmonics.

〔Example〕

FIG. 2 shows a block diagram of a spurious reduction circuit using IF harmonics according to an embodiment of the present invention, in which the input intermediate frequency and the local oscillation frequency are mixed in a mixer circuit 1 to create a transmission frequency, and the transmission frequency is After removing spurious signals outside the frequency band using a band pass filter (BPF) 3, a wireless transmitter that transmits via a high frequency amplifier 4 removes the same spurious signal as the intermediate frequency spurious signal existing within the transmission frequency band. The 1F signal creation circuit 6 to be created includes a ×3 multiplier circuit 6-1 and 32.1MIIzB P
F6-2 is used, and an amplifier 7-1 and a variable attenuator 7-2 are used in the IF signal level setting circuit 7 that sets the level of the same spurious signal to a predetermined value.

Further, a variable phase shifter 8-1 is included in the phase conversion circuit 8 for converting the phase of the level-set intermediate frequency signal, and the phase-converted intermediate frequency signal and the intermediate frequency signal in the hand output from the mixer circuit are provided. A synthesizer 9 for synthesizing the above is provided upstream of the bandpass filter 3.

In this example, the intermediate frequency is set to 1 to facilitate the explanation of the operation.
0.7MHz, and the oscillation frequency of the local oscillator 2 is 42.
The transmission frequency is 725MHz, and the difference between them is 33.025Ml1z.

FIGS. 4(a) to 4(d) show the output frequencies of each circuit, and the operation of each circuit will be explained with reference to the figures.

As shown in the figure fat, the transmission frequency is 33.025MHz
The harmonic of the intermediate frequency existing within the band corresponds to three times the IF frequency (32,1Mllz). Therefore, ×
A 3 multiplier circuit 6-1 multiplies the IF frequency 10.7MHz by 3 to create a 32.1MH2 signal, a BPF 6-2 extracts only the 32.1M1lz signal (Figure (1))), and the amplifier 7- Output to 1.

This 32.1 MHz signal is amplified by the amplifier 7-1, and then the level is adjusted to the transmission frequency 33.025 by the variable attenuator 7-2.
The signal is adjusted to have the same level as the intermediate frequency signal existing within the MHz band. This intermediate frequency signal of the same level is converted into a phase opposite to the intermediate frequency signal existing within the band in the variable phase shifter 8-1, as shown by the dotted line in Figure (C1).
It is output to the synthesizer 9.

The synthesizer 9 synthesizes the intermediate frequency signal existing within the transmission frequency band outputted from the mixer circuit 1 and the intermediate frequency signal of the opposite phase and the same level outputted from the phase conversion circuit 8 to generate an intermediate frequency signal within the transmission frequency band. This cancels the intermediate frequency signal present in the IF frequency signal and outputs a transmission frequency of 33.025 MHz with reduced spurious due to IF harmonics as shown in the figure (dl).

FIG. 3 shows a block diagram of a spurious reduction circuit using IF harmonics according to another embodiment of the present invention.

This shows a spurious reduction circuit in a case where the transmission frequency band is wide and spurious due to a large number of IF harmonics exist within the wide transmission frequency band. That is, for example, 3, 4, 5 to create the same frequency as each spurious.
X multiplier circuit 6-1-1 to 6-1-n and BPF 672
-1 to 6-2-n, amplifiers 7-1-1 to 7-1-n and variable attenuator 7- for making each spurious at the same level.
2-1 to 7-2-n and each variable attenuator 7-2-1 to 7-
Variable phase shifters 8-1-1 to 8-1-n are provided for converting the phase of the IF harmonic signal, which has the same level at 2-n, into a phase opposite to that of the corresponding spurious signal.
The operation of each circuit is performed in the same manner as described above.

This reduces the number of spurious signals present within the transmission frequency band.

〔Effect of the invention〕

As described above, according to the present invention, spurious signals due to IF harmonics existing within the transmission frequency band are reduced, and a high-quality transmission signal can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a principle block diagram of a spurious reduction circuit using IF harmonics of the present invention, Fig. 2 is a block diagram of a spurious reduction circuit using IF harmonics of one embodiment, and Fig. 3 is a block diagram of the spurious reduction circuit using IF harmonics of another embodiment. Figure 4 is a diagram showing the output frequency of each circuit in one embodiment, Figure 5 is a block diagram of the main parts of a conventional wireless transmitter, and Figure 6 is a diagram of a conventional wireless transmitter. FIG. 2 is a diagram for explaining IF harmonics in the machine. In the figure, 1 is a mixer circuit (MIX), 2 is a local oscillator (LO), 3 is a band pass filter (BPF), and 4
is a high frequency amplifier, 6 is an IF signal generation circuit, 7 is an IF signal level setting circuit, 8 is a phase conversion circuit, 9 is a synthesizer, 6-
1.6-1-1 to 6-1-n are ×3 to ×5 multiplier circuits,
6-2.6-2-1 to 6-2-n are BPF, ? -1.7
-1-1~? -1-n is an amplifier, ? -2,7-2-1~
? -2-n is a variable attenuator, 8-1.8-1-1 to B-1
-n indicates a variable phase shifter. Times g-＾7゛口1. ,7m Figure 2

Claims (1)

[Claims] A mixer circuit (1) that mixes an input intermediate frequency and a local oscillation frequency.
In a wireless transmitter that mixes the signals to create a transmission frequency, removes spurious signals outside the band of the transmission frequency with a bandpass filter (3), and then transmits through a high frequency amplifier (4), an IF signal generation circuit (6) that generates a spurious signal identical to the intermediate frequency spurious existing within the IF signal level setting circuit (7) that sets the level of the same spurious signal to a predetermined value;
The bandpass filter (3) includes a phase conversion circuit (8) that converts the phase of a signal, and a synthesizer (9) that combines the phase-converted IF signal and the in-band IF signal output from the mixer circuit. A spurious reduction circuit using intermediate frequency harmonics is characterized in that it is provided at the front stage of the circuit.