JPH0328574Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an oscillation frequency detection circuit, and more specifically, to a detection circuit that detects whether the oscillation frequency of an oscillator is located within the passband of a narrowband bandpass filter. It is.

Conventionally, integrated circuits (IC circuits)
A detection circuit as shown in FIG. 1 has been used to detect whether the oscillation frequency of a VCO (voltage controlled oscillator) is within the passband of a subsequent bandpass filter.

In Figure 1, VCO2 installed in IC1
The oscillation output is supplied through a terminal 3 and a resistor 8 externally connected to the IC 1 to a bandpass filter 4 made of a narrow band ceramic filter or the like. The oscillation output after passing through the bandpass filter 4 is supplied to a predetermined circuit at the subsequent stage, and a part of it is returned to the IC 1 via the terminal 7, and is connected to an amplifier provided in the IC 1. 5. A part of the amplified oscillation output is supplied to the AM detector 6 and detected. Note that the resistor 8 is a resistor that matches the output side resistor 9 of the bandpass filter 4.

According to the above configuration, for example, if the oscillation frequency of the VCO 2 is within the passband of the bandpass filter 4, a detection output _VH having a higher potential than the detector 6 can be obtained. Based on this detection output V _H , the control voltage V _C of the VCO 2 is controlled.

According to such a detection circuit, since the output of the bandpass filter 4 is generally at a low level,
It is necessary to provide a detection amplifier 5 in the IC 1,
It was uneconomical. In addition, since a bandpass filter 4 made of a narrow band ceramic filter is externally connected to IC1, the output of this filter is
1, a terminal 7 must be provided in addition to the output terminal 3, which is extremely uneconomical.

The present invention has been devised in view of these problems, and aims to provide an oscillation frequency detection circuit that can economically configure the detection circuit, and in particular, is extremely economical when designing integrated circuits. It is.

Embodiments of the oscillation frequency detection circuit of the present invention will be described below with reference to the drawings.

FIG. 2 shows an overall block circuit diagram according to the first embodiment of the present invention, and FIG. 3 shows waveform diagrams at various parts of FIG. In FIG. 2, parts corresponding to those in FIG. 1 are given the same reference numerals. In this embodiment, as shown in FIG. 2, the resistor 8 shown in FIG. 1 is provided in the IC 1, and the VCO 2 and the terminal 3 are connected via this resistor 8. The oscillation output derived from the terminal 3 is supplied to a narrowband bandpass filter 4 such as a ceramic filter and is waved. Note that this narrowband bandpass filter 4
is constructed so that the impedance is low for frequencies within the passband and high for frequencies outside the passband, but bandpass filters made of ceramic filters are In general, there are bandpass filters that have such characteristics, and some bandpass filters made of inductances, capacitors, etc. have the above-mentioned characteristics.

If the VCO 2 were to be caused to sweep oscillate from a low frequency to a high frequency, the output waveform at point A in the figure would be the waveform shown in FIG. 3A. Now, it is assumed that the passband frequency of the bandpass filter 4 is a frequency corresponding to the waveform of section I shown in the waveform A above. Since the bandpass filter 4 becomes a high impedance element for frequencies outside the passband, the potential difference between both ends of the resistor 8 (the potential difference between A and B) becomes small. Furthermore, since it becomes a low impedance element for frequencies within the pass band, the above-mentioned potential difference becomes large. Therefore, the output waveform at point B is as shown in FIG. 3B. That is, for frequencies outside the passband, the waveform is almost the same as the waveform of A, and attenuates to about 50% in section l, which is a frequency within the passband.

The signals at points A and B above are provided in IC1.
The signals are supplied to AM detectors 10 and 11, respectively, where they are detected and converted into a DC component. The signal waveforms converted into DC components are shown in FIGS. 3C and 3D. The DC output obtained from the wave detector 10 is supplied to the + side input terminal of a comparator 12 provided in the IC 1, and the DC output of the wave detector 11 is supplied to the - side input terminal of the comparator 12. As a result, the output V _H of the comparator 12
As a result, a high level output waveform as shown in FIG. 3E is obtained. If the oscillation frequency is outside the passband of the bandpass filter 4 in the l section of FIG. 3A,
The waveform of D in the figure is shown by a dotted line, and therefore the detection output is at a low level.

Through the above steps, it is detected whether the oscillation frequency of the VCO 2 is located within the passband of the bandpass filter 4 or not.

The waveform at the output end of the bandpass filter 4 is as follows:
As shown in Figure 3, V _put , in the l section where the frequency of the input waveform is within the passband of the bandpass filter 4, the waveform in Figure A is attenuated by about 20%, and the frequency outside the passband is attenuated by about 20%. The frequency is almost completely attenuated. This is substantially the same as the waveform at the output end of the bandpass filter 4 in the conventional oscillation frequency detection circuit shown in FIG.

In the above-described embodiment, the resistor 8 may not be provided in particular, and the drive resistor of the bandpass filter 4 may be shared.

FIG. 4 shows an overall block circuit diagram according to the second embodiment of the present invention, and FIG. 5 shows waveform diagrams at various parts in FIG.

In FIG. 4, the same parts as those in FIG. 2 are given the same reference numerals, and explanations of overlapping parts are omitted.

In FIG. 4, the signal across the resistor 8 is:
They are respectively supplied to the + side input terminal and the - side input terminal of the comparator 13 provided in the IC1. Now, assuming that the signal waveforms at both ends of the resistor 8 are as shown in FIGS. 5A and 5B, the output waveform of the comparator 13 is the difference between the two and becomes the waveform shown in FIG. 5F. The output of this comparator 13 is the AM
The signal is supplied to the detector 14, resulting in the detected output shown in FIG. 5G. This detection output is supplied to the + side input terminal of the comparator 15 provided in IC1, and is applied to the reference potential.
Compared to E ₀ . As a result, from this comparator 15,
Figure 5 The waveform of G is clipped at the _E0 potential.
A detection output V _H shown in Figure H is obtained.

In this example as well, the bandpass filter 4 provides an output waveform substantially the same as that shown by V _put in FIG. 3.

Although the embodiments of the present invention have been described above, it goes without saying that the above embodiments can be modified in various ways based on the technical idea of the present invention.

In short, the oscillation frequency detection circuit of the present invention is based on the potential difference across a resistor interposed between an oscillator and a narrowband bandpass filter configured to have high impedance for frequencies outside the passband. It is configured to detect the oscillation frequency.

As a result, since a sufficiently high-level signal before passing through the bandpass filter is used as the original signal to be detected, an economical circuit can be constructed without particularly requiring an amplifier for detection.

Also, based on the signal on the input side of the bandpass filter external to the IC, it is detected whether the oscillation frequency is located within the passband of this bandpass filter, so the detection circuit inside the IC Even in the case of

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing a conventional oscillation frequency detection circuit, FIG. 2 is a block circuit diagram showing a first embodiment of the oscillation frequency detection circuit of the present invention, and FIG. 3 is a block circuit diagram of a conventional oscillation frequency detection circuit. A diagram showing the waveforms of each part,
FIG. 4 is a block circuit diagram showing a second embodiment of the oscillation frequency detection circuit of the present invention, and FIG. 5 is a diagram showing waveforms of various parts of the block circuit diagram of FIG. 4. In addition, in the symbols used in the drawings, 2...
...VCO, 4...Narrowband bandpass filter, 8
...Resistance, 10,11,14...AM detector, 1
2, 13, 15... comparators.

Claims (1)

[Scope of utility model registration request] An oscillator, a narrowband bandpass filter configured to have high impedance for frequencies outside the passband, a resistor interposed to connect the oscillator and the narrowband bandpass filter, and this resistor. An oscillation frequency detection circuit comprising means for detecting a potential difference between both ends of the oscillation frequency detection circuit.