JPH0152922B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a frequency discriminator.

[Prior art]

FIG. 4 is a block circuit diagram of a conventional frequency discriminator. This frequency discriminator divides an input signal of amplitude E [V] and frequency f [Hz] inputted from an input terminal 1 into two by a power divider 2, and directly sends one of the two divided signals to a phase detector 3. In addition, the other signal is applied to the phase detector 3 via the delay circuit 4 whose delay time is Δt [sec], and the square-law detectors 5, 6, 7 connected to the phase detector 3 and 8 to voltage KE ² (1−sinθ)/4KE ² (1+sinθ)/4,
KE ² (1−cosθ)/4, and KE ² (1+cosθ)/
4 is the voltage KE ² sin θ/2 and
KE ² cosθ/2 is output. Here, the frequency f of the input signal and the phase angle θ of the output voltage are θ=f×△
Since there is a relationship of t×360°, the frequency f of the input signal can be determined from the output voltages of the differential amplifiers 9 and 10.

However, in such a conventional frequency discriminator,
Since the input voltage is included in the output voltages KE ² sin θ/2 and KE ² cos θ/2, the frequency is unknown for unknown input voltages. Therefore, it was necessary to remove the input voltage from the output voltage, but there was a problem in that the circuit for removing this input voltage was complicated.

Further, since the output voltage takes positive and negative values, there is a problem that division calculation using a logarithmic amplifier cannot be used.

Furthermore, the phase detector 3 increases in size as the frequency f of the input signal decreases, so it
There was a problem in that it was impossible to construct a practical frequency discriminator at frequencies below [Hz].

[Purpose of the invention]

The present invention was made to solve the above-mentioned conventional problems, and it is possible to discriminate frequencies without being affected by input signals. The purpose is to provide a frequency discriminator.

[Summary of the invention]

Therefore, in the present invention, an input signal is divided into two parts, one part is added to a first logarithmic amplifier having a predetermined amplification gain, and the other part is added to a monotonic function circuit whose frequency characteristic is a monotonic function, that is, a monotonically increasing function or a monotonically decreasing function. to a second logarithmic amplifier having the same amplification gain as the first logarithmic amplifier, and further apply the output voltages of the first and second logarithmic amplifiers to a differential amplifier, and apply only the frequency of the input signal. A dependent voltage is obtained to perform frequency discrimination of the input signal.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block circuit diagram of a frequency discriminator according to the present invention.

In FIG. 1, reference numeral 11 is a power divider, and reference numeral 12 is a power divider whose output signal is a monotonically increasing or decreasing function with respect to the frequency of the input signal. The monotone function circuits 13 and 14 are the function G(f) of the signal frequency f, and the numbers 13 and 14 are logarithmic amplifier circuits whose output voltage e ₀ is e ₀ = Klog ei + α with respect to the input voltage ei (K and α are logarithmic (constant determined by the amplification gain of the amplifier), symbol 15 is the logarithmic amplifier 13,
This is a differential amplifier that amplifies and outputs the difference between the 14 output voltages.

Next, the overall operation of the frequency discriminator shown in FIG. 1 will be explained.

The power divider 11 divides an input signal of amplitude [V] and frequency f [Hz] inputted from the input terminal 16 into two, and sends one of the divided input signals to the first logarithmic amplifier 13 and the other to the monotone function circuit. 12 to a second logarithmic amplifier 14, respectively. By inputting the input signal, the first logarithmic amplifier 13 increases the input voltage E/√
2+α, and the monotone function circuit 12 outputs the input voltage E/
√2 and outputs the voltage G(f)E/√2, and the second logarithmic amplifier 14 outputs the voltage G(r)E/√2.
Amplify the voltage KlogG(f)＋KlogE＋Klog(1/√
2) Output +α.

Next, the differential amplifier 15 amplifies the difference between the output voltage of the first logarithmic amplifier 13 and the output voltage of the second logarithmic amplifier 14, that is, the voltage −KlogG(f) to obtain the voltage −K′logG(f). Output. This output voltage −K′logG
(f) does not include the voltage component of the input signal, and monotonous function circuit 12
is a function of the amplification gain G(f), that is, the frequency f of the input signal. Therefore, the frequency f of the input signal can be easily added from the output voltage of the differential amplifier 14.

Next, FIG. 2 is a block circuit diagram showing another embodiment of the frequency discriminator according to the present invention.

Note that in FIG. 2, parts that perform the same functions as those in FIG. 1 are designated by the same reference numerals, and a description thereof will be omitted.

In this embodiment, a monotonically decreasing function is realized by a low-pass filter 17 having relatively gentle frequency characteristics.

The amplification gain G(f) of the low-pass filter 17 is G(f)=1/√1+(2) ² , where the resistance value of the resistor 18 is R and the capacitance of the capacitor 19 is C.
If 2πfRc is sufficiently larger than 1, G(f)=1/
It becomes 2πfRC. Therefore, the output voltage V of the differential amplifier 15 becomes V=K'log(2πfRC), and the frequency f of the input signal becomes f=exp(V/K'−log(2πRC)).

Next, FIG. 3 is a block circuit diagram showing another embodiment of the present invention. Note that in FIG. 3, parts that perform the same functions as those in FIG. 1 are designated by the same reference numerals, and their explanations are omitted.

In this embodiment, the active filter 20 realizes a frequency discriminator that operates in a lower frequency band than the frequency discriminator shown in FIG. Also in this embodiment, the amplification gain G(f) of the active filter 20 is G(f)=1/2πfRC. However, the resistance value of the resistor 21 is assumed to be R, and the capacitance of the capacitor 22 is assumed to be C.

In this embodiment, a low-pass filter or an active filter is used as the monotonic function circuit, but the present invention is not limited to this, and the amplification gain may be a function of the frequency of the input signal.

〔Effect of the invention〕

As described above, according to the present invention, by using a frequency discriminator whose output signal has a characteristic that the output signal is a monotone function with respect to the frequency of the input signal, an output voltage that depends only on the frequency of the input signal can be obtained. frequency can be easily distinguished.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of a frequency discriminator according to the present invention, FIG. 2 is a block circuit diagram showing another embodiment of the frequency discriminator according to the present invention, and FIG. 3 is a block circuit diagram of a frequency discriminator according to the present invention. A block circuit diagram showing another embodiment is shown in FIG. 4, which is a block circuit diagram of a conventional frequency discriminator. 12... Monotone function circuit, 13, 14... Logarithmic amplifier, 15... Differential amplifier, 17... Low pass filter, 20... Active filter.

Claims (1)

[Claims] 1 a first logarithmic amplifier having a predetermined amplification gain and into which an input signal is input; a monotonic function circuit into which the input signal is input and which has a characteristic that an output signal is a monotone function with respect to the frequency of the input signal; a second logarithmic amplifier having the same amplification gain as the first logarithmic amplifier and into which the output signal of the monotonic function circuit is input; and a second logarithmic amplifier that amplifies the difference between the output signals of the first and second logarithmic amplifiers. and a differential amplifier that outputs a signal corresponding to the frequency magnitude of the input signal.