JPH01176103A - Frequency discrimination circuit - Google Patents

Abstract

PURPOSE:To obtain a discrimination output without distortion by selecting 2nd or 1st differentiation output and the 1st or 2nd differentiation output respec tively against the binary state represented by a phase difference discrimination output and its opposite state in the phase difference point giving the discontinu ous change of 1st or 2nd phase difference detection output. CONSTITUTION:A changeover circuit 6 selects the the 2nd or 1st differentiation output D2 or D1 and the 1st or 2nd differentiation output D1 or D2 respectively against the binary state represented by a phase difference discrimination output C and its opposite state in the phase difference point giving the discontinuous change in the 1st or 2nd phase difference detection output theta1 or theta2 and outputs it switchingly. The switching output D is given to a low-pass filter 7 and the noise component at the outside of the base band caused by noise in a transmis sion line is eliminated. Then the effect of an impulse output of the 1st or 2nd differentiation output D1, D2 caused by the discontinuous change in the 1st or 2nd phase difference detection output theta1, theta2 is avoided and a frequency dis crimination output S is obtained from a low-pass filter. Thus, the frequency discrimination operation not including any distortion theoretically and not includ ing undesired harmonics is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a frequency discrimination circuit that is applied to demodulating signals frequency-modulated by analog signals, data signals, etc., and measuring frequency deviation of input signals. Regarding.

[Conventional technology and its problems]

Conventional methods for discriminating the instantaneous frequency of an input signal include a method using the tuning characteristics of a ceramic element (ceramic discriminator), a quadrature detection method, and the like.

However, these require devices that are not suitable for IC implementation, such as ceramic elements and 90° phase shift inductance elements, and even if they are used outside the IC,
In addition to there being a limit to miniaturization, the carrier wave to be processed is limited to a specific intermediate frequency, which limits its application to heterodyne receivers, which poses problems in miniaturization and generalization.

Also, it has the same frequency as the input signal, and the phase is π
Two mutually orthogonal baseband signals are extracted by frequency mixing the input signal and two local oscillation waves that differ by /2 radians, and analog multiplication of the π/2 radian shift signal of one of them and the other baseband signal A highly versatile method is a so-called orthogonal detection method in which the two multiplication outputs obtained from L are taken out and the difference between them is used as a frequency discrimination output.

However, in order to obtain a discrimination output without distortion in this method, two circuits of analog multipliers as ideal as possible are required.
, L has a large circuit scale and is not suitable for miniaturization.

[Means for solving problems]

The present invention has been made to solve the above-mentioned conventional problems, and by realizing distortion-free frequency discrimination operation without using an analog multiplier, it can be easily miniaturized and integrated into an IC. The present invention also aims to provide a frequency discrimination circuit which is excellent in versatility.

That is, the circuit of the present invention includes a local oscillation circuit 1 that obtains a local oscillation output having the same frequency as the center frequency of the input signal R, and a polarity inverter 2 that inverts the polarity of the local oscillation output and obtains a polarity inverted output ■. , the input signal R and the local oscillation output L, and the input signal R and the polarity inverted output τ are input, respectively.
In accordance with the sawtooth-shaped phase difference characteristic, which repeats a linear rise or fall with a period of 2π radian for the phase difference between the two inputs R and L, and R and τ, the first. Second phase difference detection output θ8. 1st to obtain θ2. The second phase difference detection circuits 31 and 32 input the input signal R and the local oscillation output to obtain a phase difference judgment output C that exhibits a binary judgment value for every π radian with a period of 2π radians for these phase differences. A phase difference determination circuit 4, a first . The first and second phase difference detection outputs θ1 and θ2 are inputted and the first and second differential outputs Dr and Dz are obtained by time differential operation thereof, respectively. a second differentiator 51°52; a first differentiator 51°52; Second differential output D+
. A low-pass filter 7 that removes noise components outside the baseband generated by noise to obtain a frequency discrimination output S, a human power signal R that provides a binary change in the phase difference judgment output C, and a local oscillation output. The phase difference point with the first. The first phase difference detection outputs θ1 and θ2 have a phase difference of ±π/2 radians with respect to a phase difference point that gives a discontinuous change in the sawtooth-shaped phase difference detection characteristics. Configures the second phase difference detection circuits 31 and 32 and the phase difference determination circuit 4, and
The switching circuit 6 switches the second or first phase difference detection output θ1 or θ2 to a 2-direct state indicated by the phase difference determination output C on the phase difference point where the first or second phase difference detection output θ1 or θ2 changes discontinuously, and to the opposite state. The differential output D2 or RI2 and the first or second differential output L or D2 are respectively selectively output.

[Function] A local oscillation output having the same frequency as the center frequency of the input signal R is obtained from the local oscillation circuit 1, and this local oscillation output and the input signal R are input to the first phase difference detection circuit 31, which detects the input signal R. The first phase difference detection output θ is obtained according to a sawtooth-shaped phase difference characteristic that repeats a linear rise or fall at a period of 2π radian with respect to the re-input phase difference.

Further, the local oscillation output is input to a polarity inverter 2, from which a polarity and output signal whose polarity is inverted is obtained, and each of the polarity inversion outputs and the input signal R are input to a second phase difference detection circuit 3.
2, and a second phase difference detection output θ2 is obtained according to a sawtooth-shaped phase difference characteristic that repeats a linear rise or fall at a period of 2π radian with respect to the phase difference between the human forces R and τ.

The input signal R and the local oscillation output are input to a phase difference determination circuit 4, and a phase difference determination output C is obtained that exhibits a binary determination value for every π radian with a period of 2π radians for these phase differences.

The phase difference point between the input signal R and the local oscillation output that gives a binary change in the phase difference judgment output C is the discontinuity in the sawtooth-shaped phase difference detection characteristics of the 1st and 2nd phase difference detection outputs θ1 and θ2. It has a phase difference of ±π/2 radians with respect to the phase difference point that gives the change.

1st. The second phase difference detection outputs θ1 and θ2 are the first
．． This is input to the second differentiators 51 and 52, and the first . Second differential output D+
, Dz is obtained. One of these two inputs θ1 and θ2 is selected by the switching circuit 6 in accordance with the binary state of the phase difference determination output C, and is taken out as a switching output.

That is, the switching circuit 6 selects the first or second phase difference detection output θ1.
Or, for the binary state indicated by the phase difference judgment output C on the phase difference point that gives a discontinuous change in θ2, and the opposite state, the second
Alternatively, the first differential output D2 or DI+ and the first or second differential output L or D2 are selectively output L and switched.

This switching output is input to a low-pass filter 7, where noise components outside the baseband caused by noise in the transmission circuit are removed. Second phase difference detection output θ1, θ2
The first degree second differential output D+ due to discontinuous changes in
The influence of the impulse output on 02 is avoided, and the frequency discrimination output S is obtained from the low-pass filter 7.

〔Example〕

The present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing the configuration of one embodiment of the circuit of the present invention, and FIGS. A diagram showing the phase difference detection characteristics of the second phase difference detection circuit and the output characteristics of the phase difference determination circuit, FIG. FIG. 3 is a connection diagram showing a configuration example of a second phase difference detection circuit and a configuration example of a phase difference determination circuit.

In Figure 1, R is an input signal frequency-modulated by a baseband signal containing DC, 1 is a local oscillator,
A local oscillation output having the same frequency as the center frequency of the input signal R is generated. Reference numeral 2 denotes a polarity inverter, which inputs the local oscillation output L and obtains an manually inverted polarity output, that is, an output τ having a phase difference of π radians.

31 and 32 are the first. In the second phase difference detection circuit,
The input signal R and the local oscillation output τ, and the input signal R and the polarity inverted output τ are input, and the period is 2π for each phase difference.
1. According to the sawtooth-shaped phase difference characteristic that repeats a linear rise or fall in radians. Second phase difference detection output θ1,
Emit θ2.

Reference numeral 4 designates a phase difference judgment circuit which has the characteristic of inputting the input signal R and the local oscillation output, and outputting binary judgment values "L" and "H" for each π radian with a period of 2π radians for the phase difference between the two. . C is the phase difference determination output. The phase difference point between the input signal R and the local oscillation output that causes the phase difference determination output C to change between the binary states "H"-"L" and "L"-"H" is the first. The second phase difference detection outputs θ1 and θ2 have a deviation of ±π/2 with respect to the phase point that gives a discontinuous change (vertical fall or rise) in the sawtooth-shaped phase difference detection characteristics.

1st. Examples of characteristics of the second phase difference detection circuits 31 and 32 and the phase difference determination circuit 4 are shown in FIG. 2(a).
, as shown in (b). The vertical axes in FIGS. 2(a) and (b) are the 1st. Second phase difference detection circuits 31, 32
The levels of the outputs θ1 and θ2 and the binary logic state of the output C of the phase difference determination circuit 4 are shown in Table L, and the horizontal axis represents the phase difference θ radian between the input signal R and the local oscillation output.

The characteristic shown by the solid line in FIG. 2(a) is the characteristic of θ1, and the maximum value +v1. The case where L has a minimum value of -■ and θ exhibits a sawtooth shape showing an undesirable discontinuous change at a point where θ is an integer multiple of 2π radians is shown. At this time, the characteristic of θ2 is determined by the second phase difference detection circuit 32.
Since one input τ has a phase difference of π radians with respect to the local oscillation output, the phase difference θ has a characteristic shifted by π radians from the characteristic of θ, as shown by the broken line.

As mentioned above, the characteristics of the phase difference determination output C in FIG. 2(b) are as follows: θ3. It changes at a phase difference point that is shifted by ±π/2 radians from the vertical descent point of θ2, so in the example shown in the figure, θ is π/2.
“H” at a point that is an odd multiple of radians.

It has a rectangular characteristic with alternating "L" states.

The first type with such characteristics. Second phase difference detection circuit 3
1, 32 and the phase difference determination circuit 4 are configured according to the configuration examples shown in FIGS. 3(a) and (bl), respectively, when the input signal R9, the local oscillation output L, and the polarity inverted output τ are shaped into binary logical values. realizable.

311 in Fig. 3(a) is a monostable multi-by-break that generates a sufficiently short pulse compared to the period of the input signal R in synchronization with the rising edge of L or τ as input L, and 312 as R as trigger input (T). L, monostable multivibrator 31
It is a D type flip-flop circuit that uses the pulse output of 1 as the reset input (R), and the data input (D) is in the logic state "
It is held at "H".

313 is a low-pass filter that receives the data output (b) of this flip-flop circuit 312 as input L and removes the carrier frequency component and its harmonic components of the input signal R;
The second phase difference detection outputs are θ1 and θ2.

According to the above configuration, when the input signal R rises, the D type flip-flop 1 circuit 312 inputs the data (D
) sample outputs the “H” state, so the cent state (
With the rise of L, L, and L- (Q = "H"), L and reset state g (Q - "L") are restored, so the phase difference Q of L and ■ with respect to the phase of R becomes O and θ In the range of 2π, the duty ratio of the output of the D-type flip-flop 1 circuit 312 in the "H" state is proportional to θ. Therefore, it can be seen that when this is smoothed by the low-pass filter 313, the output of the low-pass filter 313 becomes a voltage proportional to θ, L, and the characteristic shown by the solid line in FIG. 2(a) is obtained.

Figure 3 (41 in BL is an exclusive OR circuit which receives the input signal R and the local oscillation output, 42 has the output of this circuit 41 as input L, and has the same function as 313 in Figure 3(a)). A low-pass filter 43 is a level comparator that shapes the output of the low-pass filter 42 into a binary logical value, and its output becomes a phase difference determination output C.

With the above configuration, the output of the exclusive OR circuit 41 is R.
and L are in phase (θ=0) and out of phase (θ=±π)
When , all are “L” and all are “H”, respectively.
In the case of a phase difference of π/2 radians (θ=±π/2), “
Since "H" and "L" are generated at the same rate, the smoothed output by the low-pass filter 42 is θ=0.θ=±π, θ=
Each of ±π/2 exhibits triangular characteristics giving a minimum value, a maximum value, and an average value of the former two. Therefore, it can be seen that if the level comparator 43 uses the above-mentioned average value as a threshold value and performs binary judgment, the rectangular characteristic shown in FIG. 2(b) can be obtained.

Next, returning to Figure 1, 51 and 52 are the respective θ
1 and θ2 are input L, and the differential waveform thereof is output. In the second differentiator, Dl and D2 are its differential outputs. 6
inputs the differential output L, ,D2 and the phase judgment output C,
Corresponding to the binary state of C, D, ,D.

This is a switching circuit that selects and outputs either one of these, and can be configured with an analog switch. 7 is a wave device in the low range,
The output D (D or OX) of the switching circuit 6 is input L, and it is a low-pass filter L that removes noise components outside the baseband band generated at the switching output due to noise in the transmission line.
Its output S is a frequency-discriminating output consisting of a baseband signal extracted by a low-pass filtering operation.

In the above configuration, the configuration example of the circuit according to the present invention shown in FIG. 1 and the first circuit according to the present invention shown in FIGS. Configuration examples of the second phase difference detection circuit and phase difference determination circuit and the first phase difference detection circuit shown in FIGS. 2(a) and (b). Based on characteristic examples of the second phase difference detection circuit and the phase difference determination circuit, the frequency discrimination operation and effects thereof will be explained in detail using mathematical formulas and time charts.

Now, each signal θ1 in FIG. The time waveforms of θz+D++Dz+D and θ in Figure 2 are θ+(1) and θz, respectively.
(t).

Paste (t), Dz(t), D(t), θ(1)
Also, the binary states “H” and “L” of C are +
Let the time waveform replaced with 1 and 0 be C(t). Furthermore, the operation of the switching circuit 6 is as follows: C=“H” (C(t)=+
1), then Dl, and C=“L”(C(t)=
0 ) (7) When D2 is selected and output, respectively. At this time, the following relational expressions can be derived from FIGS. 1 and 2.

Dt = D+(t), c(t)+oz(t)(1-c(
t))・・・・・・・・・(5) However, L, δ (・) are,
θ2. explained in Fig. 2 using the Dirac impulse function.
It is generated by differentiation at a discontinuous point of θ2.

Here, θ0 shown in FIGS. 2(a) and (b). θ2
According to the relationship between L and C, the following formula % formula % (6) holds true, so if we summarize formulas (11 to (7)), we finally get the following formula % formula % By this formula (8), the switching output The waveform D(t) is dθ(
t)/dt, that is, it is proportional to the angular frequency deviation (denoted as Δω) from the center angular frequency of the input signal R, so D
It is clear that t) becomes the frequency discrimination output.

A specific example of the frequency discrimination operation shown by the above formula is shown below using a time chart in Fig. 4 (al, (
It becomes like bl.

Figures 4 (a) and (b) show the times when the absolute value of the angular frequency deviation Δω is relatively large (assuming Δω = ±ω) and when it is small (assuming Δω − ±ω1), respectively. The waveform is shown as L, Δω=ΔωH, ΔωL〉0. The cases where Δω=−Δω8, −Δω, and <0 are represented by solid lines and broken lines, respectively (however, ΔωH>ΔωL).

In Fig. 4 (a), the change in phase difference θ (phase rotation) is faster than in (b), so the changes in the sawtooth waves of θI (t) and θ2 (t) are (alO is better than (b)). Faster.For this reason,
These time differential waveforms Dt(t) and oz(t) are θ
1(t), θ2(L) other than the sharp downward or upward impulse train that occurs at the discontinuous point is θ1.
(t), exhibits a constant voltage L proportional to the slope of the linear slope portion of θ2(t), (a) is larger than (b). This means that if we set this constant voltage value as L and ν□ + VL for Δω-Δω and ΔωL (solid line), respectively,
Δω=−Δω,.

−Δω, (dashed line), respectively, v,, l
VL and L, and vH2vL are L according to formulas (1) to (4), and the following formula■ C□−□Δω□ ・・・・・・・・・・・・・・・
...(9)π ■ ■, =□Δω, ......
...It is clear from the fact that it is given by α0)π.

On the other hand, the above-mentioned sharp impulse train corresponds to the 0 inner cylinder 2 term on the right side of each equation (31, (4)), and its period is o +
(t) and ox(t) are generated at an angular frequency Δω, so if Δω is small, the fundamental wave component of the impulse train will be mixed into the baseband signal band of the frequency discrimination output L, and the low-pass filter 7 becomes a distortion component that cannot be removed, so it is inappropriate to perform low-pass filtering on Dl(t) or Dz(t) as they are.

Here, the phase difference determination circuit 40 determination output waveform C(t) is the second
Due to the relationship in Figures (a) and (b), Figure 4 (a),
(As shown in the second row from the bottom of bl, when an impulse of 0+(1) occurs, C(t) = 0 (C=“L”)
, when an impulse of 0X(t) occurs, c(t) = +H
C-“H”).

Therefore, the input DI (t), o of the switching circuit 6 in FIG.
If the switching output operation logic of 2(t) is configured as follows, D(t) is effectively expressed by equation (5) and becomes 0. Since the switching output waveform alternately avoids the impulse generation points of (1) and D2(t), the output waveform shown in FIG.
), as shown at the bottom of (b), D(t) has the following:
Does not include distortion within the baseband signal band, and frequency discrimination output ±Δω83. A constant output ±v proportional to ±Δω.

, ±VL can be obtained, respectively.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to theoretically obtain a frequency discrimination operation without distortion and without unnecessary harmonics. In addition, in order to realize this, there is no need for two local oscillation outputs with a phase difference of π/2 radians from each other, which were required in the conventional quadrature detection method, or an analog multiplier, etc., as a local oscillation circuit. amplifier, level comparator,
Circuits can be formed by applying technologies such as analog switches, logic circuits, etc. as main components, linear ICs, swissotide capacitor circuits, and CMOS circuits, and the circuit scale is small, making it suitable for ICs and miniaturization and low power consumption. . Furthermore, in terms of applications, it has the advantage of being excellent in versatility, as it can be applied not only to superheterodyne receivers but also to receivers that convert received waves directly into the baseband domain.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of one embodiment of the circuit of the present invention, and FIGS. FIGS. 3(a) and 3(b) are diagrams showing the phase difference detection characteristics of the second phase difference detection circuit and the output characteristics of the phase difference determination circuit, respectively. A connection diagram showing a configuration example of a second phase difference detection circuit and a configuration example of a phase difference determination circuit, FIG. 4(a),
(b) is a time chart showing examples of time waveforms when the absolute value of the angular frequency deviation Δω of the input signal is relatively large and small, respectively. ■...Local oscillation circuit, R...Input signal, L...Local oscillation output, 2...Polarity inverter, L... Polarity inversion output, 31.32...
...First. Second phase difference detection circuit, θ1, θ2...
...The first thing. Second phase difference detection output, 4...
Phase difference judgment circuit, C... Its phase difference judgment output,
51.52...1st. Second differentiator, D+,
Dz...The first. Second differential output, 6...
...Switching circuit, D...Switching output, 7...
・Low pass filter, S... Frequency discrimination output. (obtained --------VH9q amount (b) --------1---1--Vi.

Claims (1)

[Claims] A local oscillation circuit 1 that obtains a local oscillation output L having the same frequency as the center frequency of the input signal R, a polarity inverter 2 that inverts the polarity of the local oscillation output L and obtains a polarity inverted output @L@, and an input signal R. Local oscillation output L, input signal R and polarity inverted output @L@ are input respectively, and two inputs R and L are respectively input.
, the first and second phase difference detection outputs θ_1 and θ_2 are obtained in accordance with a sawtooth-shaped phase difference characteristic that repeats a linear rise or fall at a period of 2π radian with respect to the phase difference between R and @L@.
, input the input signal R and the local oscillation output L to the second phase difference detection circuits 31 and 32, and obtain a phase difference judgment output C that exhibits a binary judgment value for every π radian with a period of 2π radians for these phase differences. A first circuit inputs the phase difference determination circuit 4 and the first and second phase difference detection outputs θ_1 and θ_2 and obtains first and second differential outputs D_1 and D_2, respectively, by time differentiation operation thereof.
, second differentiators 51 and 52, and first and second differential outputs D_1
, D_2 and selects one of these two inputs corresponding to the binary state of the phase difference judgment output C to obtain these switching outputs D. It consists of a low-pass filter 7 that removes noise components outside the baseband caused by noise and obtains a frequency discrimination output S, and an input signal R and a local oscillation output L that provide a binary change in the phase difference judgment output C. The first phase difference point has a phase difference of ±π/2 radian with respect to the phase difference point that gives a discontinuous change in the sawtooth-shaped phase difference detection characteristics of the first and second phase difference detection outputs θ_1 and θ_2. , constitutes the second phase difference detection circuits 31 and 32 and the phase difference determination circuit 4, and
The switching circuit 6 provides a second or first differential for the binary state indicated by the phase difference determination output C on the phase difference point that gives a discontinuous change in the first or second phase difference detection output θ_1 or θ_2, and the opposite state. A frequency discrimination circuit configured to select and switch output D_2 or D_1 and first or second differential output D_1 or D_2, respectively.