JPH03128465A - Frequency detecting circuit - Google Patents

Abstract

PURPOSE:To detect positive and negative angular frequencies by multiplying an input ted complex signal and a complex conjugate signal having a specified frequency charac teristic to the aforementioned complex signal and detecting a frequency of the complex signal from the multiplication output. CONSTITUTION:The signal come from an input terminal 21 is inputted to multiplying devices 31A, 31B of an orthogonal detecting circuit 26, and 2 cosomega2t, 2sinw2t are sup plied to the multiplying circuits 31A, 31B from input terminals 33A, 33B respectively. The input signals are orthogonally detected by the circuit 26 to obtain signals I, Q, from which a real number part and imaginary number pat of the input signals are obtained then respectively supplied to a filter circuit 23A and imaginary number part filtering circuit 23B. Next, an output of the circuit 23B is inverted through an inverter 24, thereby the complex coupling of the output through the circuit 23 is obtained. Then, the outputs of multiplying devices 33, 34 are supplied to a subtracting device 37 and the outputs of multiplying devices 35, 36 are supplied to an adding device 38. Outputs of the real part and imaginary part are obtained respectively from the subtracting device 37 and adding device 38, and the outputs are supplied to an angular frequency detecting device 27 wherein the frequency is obtained from an output of multiplying device 22.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency detection circuit used in an AFC (automatic frequency control) circuit or a frequency pull-in loop.

[Summary of the invention]

This invention provides an input complex signal and a frequency detection circuit used in an AFC circuit or a frequency pull-in loop.
By multiplying the input complex signal by a complex conjugate signal of a signal with predetermined frequency characteristics and detecting the frequency from the multiplication output, it is possible to detect both positive and negative angular frequencies. It was made possible to do so.

[Conventional technology]

When configuring an AFC (automatic frequency control) circuit or a frequency pull-in loop, a frequency detection circuit that detects the frequency of a human input signal is required. In conventional AFC circuits and frequency pull-in loops, FM detection circuits such as quadrature detection circuits and PLL detection circuits are used as frequency detection circuits.

However, in FM detection circuits such as quadrature detection circuits and PLL detection circuits, a signal whose frequency can be detected must be on the carrier, and the detectable frequency is within the range of positive angular frequencies or the range of negative angular frequencies. limited to one side.

[Problem to be solved by the invention]

As described above, the conventional frequency detection circuit using the FM detection circuit cannot detect negative angular frequencies as well as positive angular frequencies. That is, in such a frequency detection circuit, the detectable frequency range Fs is as follows: f aAll < f amt < f sawflIM, where f is the highest frequency that can be detected, and f sin is the lowest frequency that can be detected.
, 1 ・f, , 3I>0.

For this reason, there is a problem in that it is not possible to form a frequency pull-in loop that detects the frequency of an input signal over a positive and negative range, with the center frequency set to 0Hz, and drives the frequency to, for example, 07.

Further, such a conventional frequency detection circuit has a problem in that the output level varies with DC input (input at frequency 07).

Therefore, an object of the present invention is to provide a frequency detection circuit that can detect positive angular frequencies and negative angular frequencies.

Another object of the present invention is to provide a frequency detection circuit that does not cause variations in output level due to DC input.

[Means to solve the problem]

This invention multiplies an input complex signal by a complex conjugate signal of a signal that has predetermined frequency characteristics for the input complex signal, and detects the frequency of the input complex signal from the multiplication output. This is a frequency detection circuit characterized in that:

[Effect]

Complex baseband signal exp(j(ω. 10.)) ω. : is the angular frequency θ. : When the initial phase is passed through a filter with amplitude characteristic A(ω) and phase characteristic -φ(ω), A(ω.)・exp(j(ω.t+θ.−φ(ω.))
), when the complex conjugate signal of the signal passed through this filter is multiplied by the input complex baseband signal, A(ω.

)・exp (jφ(ω.)).

In this way, when the input complex baseband signal is multiplied by the complex conjugate signal of a signal that has a predetermined frequency characteristic with respect to the manually input complex baseband signal, it becomes a function only of the angular frequency.

Therefore, this allows the angular frequency of the complex baseband signal to be determined.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

First, the basic structure of the present invention will be explained with reference to FIG.

As shown in FIG. 1, a complex baseband signal is supplied to the input terminal l, and the complex baseband signal from the input terminal 1 is supplied to the multiplier circuit 2. The signal is supplied to the multiplier circuit 2 via the filter circuit 3 and the complex conjugate circuit 4 having the characteristics ω)), and the output of the multiplier circuit 2 is taken out from the output terminal 5. In this way, from the output of output terminal 5,
The frequency of the input signal can be detected.

That is, in FIG. 1, it is assumed that a complex baseband signal X x =exp (j (ω.t+θo))...■ with a constant amplitude value is supplied to the input terminal l. In addition, ω. is the angular frequency, θ.

is the initial phase. The complex baseband signal X from this input terminal 1 is supplied to one input terminal of a multiplier circuit 2 and is also supplied to a filter circuit 3.

When the complex baseband signal X from the input terminal l is passed through the filter circuit 3, it becomes
φ(ω.))) ...■.

In the complex conjugate circuit 4, the complex conjugate of the output of the filter circuit 3 is taken, and from the complex conjugate circuit 4, I A(ωe> I
exp(-j ωot-jθo ten jφ(ω.))...
・■ is obtained.

The multiplier circuit 2 multiplies the complex baseband signal from the input terminal 1 (represented by equation 0) and the output of the complex conjugate circuit 4 (represented by equation 0). This multiplied signal y is y=lA(ω.)1・exp(jφ(ω.))...■
becomes.

As can be seen from equation 0, the output y of the multiplier circuit 2 is ω. When there is a one-to-one correspondence between and y, the angular frequency ω of the human-generated complex baseband signal. It becomes a function of only. Therefore, the angular frequency ω of the complex baseband signal input from this output signal y. can be found.

In the above example, the filter circuit 3 is used, but instead of the filter circuit 3, a delay circuit 3A may be used as shown in FIG. Delay circuit 3A
is expressed as A(ω) =exp(-τω), the amplitude characteristic is A(ω)1=1, and the phase characteristic is 1φ(ω)-τω. When such a delay circuit 3A is used, the phase characteristic becomes linear with respect to the angular frequency.

Further, as shown in FIG. 3, the complex baseband signal from the input terminal 1 is filtered by a filter circuit 13A having different characteristics.
and 13B, the output of the filter circuit 13B is supplied to the multiplication circuit 12, the output of the filter circuit 13A is supplied to the multiplication circuit 12 via the complex conjugate circuit 14, and the output of the multiplication circuit 2 is supplied from the output terminal 15. You may also take it out.

In this case, if the characteristics of the filter circuit 13A are I Al (ω) I exp (-jφ, (ω)) and the characteristics of the filter circuit 13B are Az (ω) l exp (-jφ, (ω)),
From the output terminal 15, 18, (ω) IIA, (ω) ・exp (j (φ, (ω) − φt (ω))) is output 0 For example, Al (ω) = jω bar jω + a) lh (ω) = 5ω bar jω+b), then the output from the output terminal 15 is ω2 expcJ(tan-'(a/ω) (m57./-i ear "-tan-' (b/ω)) ) In this case, for example, if bypass filters having different time constants are used as the filter circuits 133A and 13B, the DC component is cut, so that the problem of input DC offset does not occur.

Next, a specific configuration of a frequency detection circuit to which the present invention is applied will be explained.

FIG. 4 shows an embodiment of the present invention. Fourth
In the figure, the signal from the input terminal 21 is transmitted to the quadrature detection circuit 2.
6. The quadrature detection circuit 26 includes multipliers 31A and 31B and low-pass filters 32A and 32B. The multiplier 31A is connected to the input terminal 33A (
2cos ω,t) is supplied. The multiplier 31B has
(-2 sin ωzt) is supplied from the input terminal 33B. The input signal is orthogonally detected by the orthogonal detection circuit 26,
I.

A Q signal is obtained. The real part and imaginary part of the input signal are obtained from the I and Q signals. In other words, the input terminal 21 (c
When osω, 1+θ) is supplied, (ωco=ω1−ωt
), from the low-pass filter 32A, cos
(ω, is 10) is obtained, and this is taken as the real part. Further, from the low-pass filter 24B, 5 inches (ω, t+θ
) is obtained, which is taken as the imaginary part.

The output of the quadrature detection circuit 26 is supplied to the filter circuit 23 and also to the multiplication circuit 22 .

The filter circuit 23 includes a real part filter circuit 23A and an imaginary part filter circuit 23B.

For example, the amplitude characteristic of the filter circuit 23 is IA(ω)l-
1 and the phase characteristic is φ(ω) = 2 tan-' (ω/a), this can be expressed as A(ω)=(jω-a)/(jω+8)a>Q. Low-pass filter 32A of quadrature detection circuit 26
The real part output from the low-pass filter 32B is supplied to the filter circuit 23A, and the imaginary part output from the low-pass filter 32B is supplied to the imaginary part filter circuit 23B.

A real part output is obtained from the filter circuit 23A, and an imaginary part output is obtained from the filter circuit 23B. The output of filter circuit 23B is inverted via inverter 24. As a result, the complex conjugate of the output passed through the filter circuit 23 is obtained.

The multiplier circuit 22 multiplies the real part and imaginary part outputs from the low-pass filters 32A and 32B of the quadrature detection circuit 26 by the real part and imaginary part outputs passed through the filter circuit 2-3 and the inverter 24. . This multiplication circuit 2
2 includes multipliers 33 to 36, a subtracter 37, and an adder 38.
It consists of

The multiplier 33 is supplied with the output of the low-pass filter 32A and the output of the filter circuit 23A.

The subtracter 37 is supplied with the output of the low-pass filter 32B, the output of the 0 multiplier 33 to which the output of the inverter 24 is supplied, and the output of the multiplier 34.

The multiplier 35 is supplied with the output of the low-pass filter 32B and the output of the filter circuit 23A.

An adder 38 is supplied with the output of the low-pass filter 32A, the output of a 0 multiplier 35 to which the output of the inverter 24 is supplied, and the output of the multiplier 36.

A real part output is obtained from the subtracter 37. Adder 38
The output of the imaginary part is obtained from . The output of the subtracter 37 and the output of the adder 38 are supplied to the angular frequency detection circuit 27.

The angular frequency detection circuit 27 determines the frequency from the output of the multiplier 22.

Note that a delay circuit may be used instead of the filter circuit 23. If a delay circuit is used, a completely linear output can be obtained.

FIG. 5 shows another embodiment of the invention. In the configuration shown in FIG. 4, frequency detection is performed by determining the real part and the imaginary part. In this case, −π≦φ(ω)≦π
A linear output can be obtained within the range of . In particular, if a delay circuit is used instead of the filter circuit 23, a completely linear output will be obtained.

However, in such a configuration, since frequency detection is performed using the real part and the imaginary part, the circuit configuration becomes complicated.

In the embodiment shown in FIG. 5, the circuit configuration is simplified by detecting the frequency using only the output of the imaginary part.

In FIG. 5, a signal from an input terminal 41 is supplied to a quadrature detection circuit 46. In FIG. The quadrature detection circuit 46 includes a multiplier 51
A and 51B, and low-pass filters 52A and 52B, the 0 multiplier 5IA is supplied with (2 cos met) from the input terminal 53A, and the 0 multiplier 51B is supplied with (2 sin ωd) from the input terminal 53B. be done. The input signal is orthogonally detected by the orthogonal detection circuit 46,
I and Q signals are obtained. These I and Q signals are made into a real part and an imaginary part.

The output of the quadrature detection circuit 46 is supplied to the filter circuit 43 and also to the multiplication circuit 42 .

The filter circuit 43 includes a real part filter circuit 43A and an imaginary part filter circuit 43B.

The real part output from the low-pass filter 52A is supplied to a filter circuit 43A, and the imaginary part output from the low-pass filter 52B is supplied to an imaginary part filter circuit 43B.

A real part output is obtained from the filter circuit 43A, and an imaginary part output is obtained from the filter circuit 43B. The output of the filter circuit 43 is supplied to the multiplication circuit 42 .

The multiplication circuit 42 is configured to obtain a multiplication output for only the imaginary part by combining the real part and imaginary part outputs from the low-pass filters 52A and 52B of the quadrature detection circuit 46 and the real part and imaginary part outputs of the filter circuit 43. Ru. Note that by using the subtracter 55, the complex conjugate of the output of the filter circuit 43 can be obtained. This multiplication circuit 42 includes multipliers 53 and 54 and a subtracter 55.

The multiplier 53 is supplied with the output of the low-pass filter 52A and the output of the filter circuit 43B.

The multiplier 54 is supplied with the output of the low-pass filter 52B and the output of the filter circuit 43A. The output of multiplier 53 and the output of multiplier 54 are supplied to subtracter 55 .

An imaginary part output is obtained from the subtracter 55. This output is output from the output terminal 56. The frequency is detected using the output of this imaginary part.

For example, if the amplitude characteristic of the filter circuit 43 is A(ω)1=1 and the phase characteristic is φ(ω)=2jan-' (ω/a), the output of the output terminal 56 is ll1(IA ((J)O)
l ・exp(j2tan-' (ωo/a)))=
sin (2tan-' (ωo/a)).

This can be expressed graphically as shown in FIG. 6. As shown in FIG. 6, a substantially linear output can be obtained in the range -a<ωo<a.

This invention can be applied not only to signals with a single frequency but also to signals with a band.

As shown in FIG. 7, the complex human power signal from the input terminal 51 and the complex human power signal passed through the τ delay circuit 53 and the complex conjugate circuit 54 are multiplied by the multiplication circuit 52, and the average value of the output of the multiplication circuit is is obtained by the averaging circuit 55, and the imaginary part of the output of the averaging circuit 55 is taken by the imaginary part circuit 56 and outputted from the output terminal 57.

In this way, the frequency of the complex human power signal having a band can be detected.

That is, the complex input signal S from the input terminal 51.

When the input signal x (t) is delayed by the τ delay circuit 53, the output of the τ delay circuit 53 becomes x(−τ)・...@ When the complex conjugate of the output of this τ delay circuit 53 is determined by the complex conjugate circuit 54, it becomes x(t-τ)...@. The output of this complex conjugate circuit 54 and the input terminal 51
When the input signal S from the multiplication circuit 52 is multiplied by the input signal S, the multiplication output becomes x (L) x(-τ)...O.

When the average value of the output of the multiplier circuit 52 is obtained by the averaging circuit 55, it becomes E (x(t)x(t-τ))...■, and when the imaginary part of the average value output is taken by the imaginary part circuit 56, , sa=-cm(E (〒(t)・x(t-r))
) ...@).

Each of the above signals is rewritten from the time domain to the frequency domain. Let the input signal SI be S, =X(ω)...■', where the input signal X(ω) is a signal with a band. When this input signal X(ω) is delayed by τ, it becomes・e-Jta...■' becomes.

When the input signal is multiplied by the complex conjugate input signal delayed by τ, the multiplication on the time axis becomes a convolution integral on the frequency axis, so the multiplied signal becomes as follows.

Taking the average value of this multiplication output, we get Then, if we take the imaginary part of this average value, we get:

This is the spectrum of the input signal (IX(ω)),
This means that weighting is performed on the frequency axis by (sinτω) and this is integrated. That is, for example, the input signal spectrum (IX(ω)12) of the component as shown in FIG. 8A is weighted on the frequency axis by (slnτω) as shown in FIG. 8B. When weighted in this way, the 8th
This results in a component on the frequency axis as shown in Figure C. When this is integrated, a signal corresponding to the polarity of the frequency of the input signal is detected, as shown in the eighth diagram.

In the above embodiment, the imaginary part circuit 56 is provided after the average value circuit 55, but the average value circuit 55 may be provided after the imaginary part circuit 56.

〔Effect of the invention〕

According to this invention, positive angular frequencies and negative angular frequencies can be detected.

Further, according to the present invention, variations in output level at a frequency of OHZ do not occur.

[Brief explanation of the drawing]

Figures 1 to 3 are block diagrams used to explain the principle of the invention, Figure 4 is a block diagram of one embodiment of the invention, Figure 5 is a block diagram of another embodiment of the invention, and Figure 6. is a graph used to explain another embodiment of the present invention, FIG. 7 is a block diagram of still another embodiment of this invention, and FIG. 8 is a graph used to explain still another embodiment of this invention. Explanation of main symbols in the drawings 1: Input terminal, 2: Multiplier circuit. 3: Filter circuit, 4: Complex conjugate circuit.

Claims (1)

[Claims] The input complex signal is multiplied by a complex conjugate signal of a signal having a predetermined frequency characteristic for the input complex signal, and the frequency of the input complex signal is detected from the multiplication output. A frequency detection circuit characterized by: