JPH05191351A - Heterodyne receiver - Google Patents

Abstract

PURPOSE:To obtain the heterodyne receiver with a wide lock range for automatic frequency control and with high sensitivity CONSTITUTION:This receiver is provided with a 1st frequency discriminator 9a for a real signal, a 2nd frequency discriminator 9b for an image signal, and a means to implement automatic frequency control for an oscillator 3 with a differential output of the frequency discriminators. Or a level detector for the image signal is provided and a means to shift the oscillating frequency of the AFC by a prescribed value when a detection output is in existence.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heterodyne receiver used in, for example, a coherent optical transmission system.

[0002]

2. Description of the Related Art In a coherent optical transmission system, heterodyne detection is performed in which signal light and local light are mixed and then detected by a photodetector. Normal local light power is 10 ^{4 of} signal light power.
10 ⁶ times stronger, the signal current from the photodetector is proportional to the product of the signal optical field and the local light field. Therefore, the signal photocurrent is
Amplified 10 ² to 10 ³ times, 10 to 30 compared to the direct detection method
dB can be received with high sensitivity. Further, in the coherent optical transmission system, the wavelength of the local oscillation light is tuned and mixed with the signal light for detection, so that a desired channel can be selected in the electric stage. Since an electrical filter having excellent characteristics can be used instead of an optical filter, frequency selectivity is significantly improved. As described above, the coherent optical transmission system is expected to have a significant performance improvement as compared with the conventional intensity modulation / direct detection system, and is therefore regarded as a promising means for realizing the next-generation large-capacity optical communication system.

In the coherent optical transmission device, the receiver is provided with a local light source in order to perform the above-mentioned optical heterodyne detection. This corresponds to a local oscillator in wireless communication. In order for the local oscillator light source to generate light having a frequency that is deviated from the signal light by an intermediate frequency, an AFC circuit (Automatic Frequency Control) that causes the frequency of the local light to follow the frequency of the signal light.
y Control: Automatic frequency control).

A conventional heterodyne receiver is shown in FIG.
There was something like that. This type of technology is disclosed in, for example, "Japanese Patent Laid-Open No. 2-235450 Optical Heterodyne Homodyne Detection Communication Method". In FIG. 7, 1 is a signal light,
2 is a local light source, 3 is a local light source, 4 is a 3 dB coupler, 5 is a balanced type light receiver, 6 is a preamplifier, 7 is an AGC amplifier (Automatic Gain Control), 8 is a demodulation circuit, and 9 is frequency discrimination. , 10 is a differential amplifier, 11 is a loop filter, and 12 is an AFC circuit.

The operation of a conventional heterodyne receiver will be described below. The frequency, phase or intensity modulated signal light 1 is multiplexed with the local light 2 by the 3 dB coupler 4. The two combined outputs of the 3 dB coupler 4 are made incident on the balanced photodetector 4 and converted into an electric signal which is an intermediate frequency signal. The intermediate frequency signal is amplified to a predetermined amplitude by the preamplifier 6 and the AGC amplifier 7, one of which is input to the demodulation circuit 8 and the other of which is input to the AFC circuit 12. In the AFC circuit 12, the frequency discriminator 9 converts the frequency of the input intermediate frequency signal into a voltage. The differential amplifier 10 compares the voltage generated by the frequency discriminator 9 with a predetermined reference voltage (0V in this example) and generates an error signal. This error signal is fed back to the local light source 3 via the loop filter 11. That is, the AFC circuit 12
Is to control the oscillation frequency of the local light source and always perform feedback so that the intermediate frequency becomes a predetermined value. The local light source is, for example, a DFB-LD (Dist.
ributed feedback laser diode) and its drive circuit, the oscillation frequency can be changed by changing the ratio of the currents injected into the two electrodes.

Next, the frequency discriminator 9 which plays a major role in the AFC circuit 12 will be described. The frequency discriminator is required to have a wide band and high sensitivity. As an example, Fig. 9 (a) shows the frequency characteristics of an ideal frequency discriminator. This is an example when the zero point (frequency at which the output voltage becomes 0V) is ± 3fc / 4 [Hz]. The actual frequency discriminator 9 is often composed of the circuit shown in FIG. This circuit is well known as a differential detection circuit. In FIG. 8, 31 is an input terminal, 32 is an output terminal, 33 is a two-branch circuit, 34 is a delay line, 35 is a double balanced mixer, and 36 is a low-pass filter.
Now, the input signal applied to the input terminal 31 is represented by the equation (1). Vin (t) = Acos ωt (1) This input signal causes the output signal V appearing at the output terminal 32.
out (t) is given by the following equation (2). Vout however ^{(t) = (A 2/} 4) · cosωt · cosω (t-τ) (2), τ is the delay time caused by the delay line 34.

Signal Vout after passing through the low pass filter 36
Is the value of the following expression (3). ^{Vout = (A 2/8)} · cosωτ = Vo cosωτ (3) which shows the transmission characteristic that varies periodically depending on the delay time tau. This is shown in FIG. 9 (b). Compared to the ideal characteristics shown in Fig. 9 (a), the frequency pull-in range is narrower and there are several zero points. Here, FIG. 9B shows the case of the equation (4). τ = 1 / fc (4) Further, FIG. 9C shows the case of the equation (5). τ = 1 / (3fc) (5)

The intermediate frequency signal is 3fc / 4 ± fc / 4 [H
z] (the portion indicated by the thick line in FIGS. 9B and 9C), the AFC circuit operates so that the intermediate frequency is pulled to 3fc / 4 [Hz] indicated by the point A1. In the case of Fig. 9 (b), the frequency pull-in range of the frequency discriminator is ± fc / 4 [H
z], the frequency pull-in range of the frequency discriminator in the case of FIG. 9C is ± 3fc / 4 [Hz]. However, since the output voltage characteristics of the frequency discriminator of FIG. 9 (b) and the frequency discriminator of FIG. 9 (c) are opposite to each other, the input to the differential amplifier 10 is properly used for the positive phase / negative phase. There is a need.

By the way, a laser diode which is a local light source has an oscillation frequency of about 10 GH with respect to a temperature change of 1 ° C.
It is a very unstable oscillator in which z also fluctuates. When the power of the heterodyne receiver is turned on, the temperature is usually stabilized to some extent by temperature control so that the local light source can capture the signal light, but the frequency of the signal light also fluctuates, so The frequency relationship of light emission is generally uncertain. Hereinafter, description will be given using the frequency spectrum in FIG. As shown in FIG. 10 (a), if the frequency of the local oscillation light when the power is turned on is lower than the signal light, the intermediate frequency becomes a positive region (on the frequency axis) as shown in FIG. 10 (b). Appears on the real signal side). When the frequency characteristic of the frequency discriminator is ideal as shown in Fig. 9 (a), the intermediate frequency is the desired frequency fs-fL (>
Correctly locked to 0). If the local light is on the higher frequency side than the signal light as shown in Fig. 10 (c), the intermediate frequency is
It appears in the negative frequency domain of 0 (d) (on the image signal side).
In the vicinity of fs-fL (<0), which is the zero point on the image signal side, the characteristics of the frequency discriminator are opposite to those on the real signal side, so that correct control cannot be performed. When a frequency discriminator that is conventionally used and has the characteristics shown in FIG. 9 (b) is used, the intermediate frequency is intended to be locked to the frequency A1, but depending on the frequency of the local light when the power is turned on, the frequency A2 or It will be locked to the wrong frequency A3.

[0010]

As described above, the laser diode, which is a local light source, has an extremely low oscillation frequency stability against temperature fluctuation and is an extremely unstable oscillator. An AFC circuit having a wide pull-in range is required for the receiver. If the characteristic of the frequency discriminator that determines the pull-in range of the AFC circuit is ideal as shown in FIG. 9 (a), the frequency pull-in range of the AFC circuit will be very wide. However, the frequency characteristic of the conventional frequency discriminator is as shown in FIG. 9 (b), and the frequency pull-in range is only ± fc / 4 [Hz]. If the delay time τ is reduced, the pull-in range can be expanded to ± 3fc / 4 [Hz] as shown in FIG. 9C, but the change of the output voltage with respect to the frequency change becomes small. That is, the sensitivity becomes poor. Therefore, the conventional AFC circuit has a problem that the frequency pull-in range cannot be expanded without deteriorating the sensitivity. Further, as described above, there is a problem that the tuning range is narrow and there is a possibility of locking at the wrong frequency.

The present invention has been made in order to solve the above problems, and so far, the AFC has been applied only to real signals.
It was not possible to operate, but AF was also applied to the image signal.
The purpose is to enable the C operation. That is, an object is to provide a heterodyne receiver in which the frequency pull-in range of the AFC circuit is expanded.

It is another object of the present invention to provide a heterodyne receiver including an AFC circuit which judges that an image signal has been received and automatically changes to a real signal receiving state. Further, it is an object of the present invention to provide a heterodyne receiver including a frequency discriminator whose frequency pull-in range is widened without deteriorating the sensitivity of frequency discrimination.

[0013]

According to the invention of claim 1, a heterodyne receiver according to the present invention comprises a first frequency discriminator for a real signal and a second frequency discriminator for an image signal. In addition, means for performing automatic frequency control (AFC) of the oscillator by the differential output of these frequency discriminators is provided. Further, in the invention of claim 2, the oscillation frequency is controlled by the frequency discriminator for the real signal, and the level detector for the image signal is provided. When the image signal is above the set level, the AFC is performed.
A means for moving the oscillating frequency of 1 by a constant value is provided. According to the invention of claim 3, as a frequency discriminator used in a heterodyne receiver, a plurality of delays having a weighting coefficient partially and having a delay time relationship of only even functions or a delay time relationship of only odd functions are provided. A frequency discriminator composed of a detector and an adder for adding the outputs of the detectors was used.

[0014]

According to the present invention, the frequency is controlled by the differential output of the frequency discrimination result of the real signal and the frequency discrimination result of the image signal. According to the second aspect of the invention, the frequency is controlled based on the result of frequency discrimination of the real signal, and when it is determined that the signal is an image signal, the control frequency moves by a constant value. In the invention of claim 3, the frequency discrimination is performed by the delay time approximated by the Fourier series expansion approximation only by the even function or only the odd function.

[0015]

EXAMPLES Example 1. FIG. 1 shows an embodiment corresponding to claim 1. In the figure, 1 is a signal light, 2 is a local light, 3 is a local light source, and 13 is a light 90 ° hybrid. 5a and 5b are balanced photodetectors, 6a and 6b are preamplifiers, 7a and 7b are AGC amplifiers, and 14 is electrical 90 °
It is a hybrid. Reference numerals 8a and 8b are demodulation circuits, 15 is an inversion circuit, and 16 is an addition circuit. Further, 9a and 9b are frequency discriminators, 10a is a differential amplifier, 11 is a loop filter, 17 is an image rejection receiving circuit, and 12a is an AFC circuit.

FIG. 2 shows details of the optical 90 ° hybrid 13 in FIG. In FIG. 2, 54 is a 3 dB coupler, 55a and 55b are polarization splitters, 51a and 51b are input terminals, and 52a, 52b, 53a and 53b are output terminals. The optical 90 ° hybrid 13 is, for example, “TGHo
dgkinson, RAHarmon, DWSmith, PJChidgey, ■ In-pha
se and quadrature detection using 90 ° opticalhybr
id receiver: experiments and design considerations
■, IEE Proceedings, vol.135, Pt.J, No.3, June 1988 ”
In detail. This is because the light input from the input terminals 51a and 51b is combined, and the output thereof appears at the output terminals 52a and 53a with a phase difference of 90 °. The optical 90 ° hybrid shown here is configured to output complementary outputs to the output terminals 52b and 53b that are 180 degrees out of phase with the output terminals 52a and 53a in order to correspond to the balanced type photodetector. Further, the light incident on the input terminal 51a is controlled so as to be circularly polarized light, and the light incident on the input terminal 51b is controlled so as to be linearly polarized light inclined by 45 ° with respect to the main axes of the polarization splitters 55a and 55b. It is assumed that The polarization states may be reversed between the input terminals 51a and 51b.

The operation of FIG. 1 will be described. The image removal receiver circuit 17 is a circuit in which the image removal receiver in microwave communication is replaced with optical communication. This kind of technology
For example, “Terumi Chika, Shigeki Watanabe, Takao Naito, Hideo Kuwahara,”
Optical Heterodyne Image Removal Reception Method ", 198
9th IEICE Spring National Convention, B-757 ”. The light 90 ° hybrid 13 combines the signal light 1 and the local light 2 to form a balanced type light receiver 5
Heterodyne detection at a and 5b respectively. The obtained two intermediate frequency signals are preamplifiers 6a, 6b and A
The signals are amplified by the GC amplifiers 7a and 7b and combined by the electric 90 ° hybrid 14, and one outputs a real signal and the other outputs an image signal. As shown in FIG. 10, if the center frequency of the signal light is fs and the center frequency of the local light is fL,
The real signal is an intermediate frequency signal obtained when fs> fL, and the image signal is an intermediate frequency signal obtained when fs <fL. The real signal is demodulated into a baseband signal by the demodulation circuit 8a. On the other hand, the image signal is demodulated into a baseband signal by the demodulation circuit 8b, and then the sign is inverted by the inversion circuit 52. The respective baseband signals are added by the adder circuit 53 and become the final demodulated output.

As for the AFC circuit 12a, the real signal and the image signal are supplied to the frequency discriminators 9a and 9a, respectively.
The frequency / voltage conversion is performed at b, and it is input to the differential amplifier 10a to generate an error signal. The error signal is the loop filter 11
After passing through, the light is returned to the local light source 3. Here, it is assumed that the frequency discriminators 9a and 9b have the same frequency characteristic, and the frequency characteristic is as shown in FIG. 3 (a) (the frequency characteristic of the frequency discriminator is the same as that in the third embodiment. Details). When controlling the intermediate frequency signal to have the frequency of point A or point Ai, in the conventional AFC circuit,
As shown in FIG. 3 (a), in the image signal area (the area on the left side of the figure in which the frequency is negative), the direction of control was opposite to that of the real signal, and it was not possible to correctly lock to Ai. On the other hand, in the configuration of the present invention, since the differential outputs of the frequency discriminator 9a and the frequency discriminator 9b are used, the frequency characteristic is as shown in FIG.
In the vicinity, the control direction is the same as when receiving a real signal. Therefore, it is possible to lock to the same intermediate frequency regardless of whether a real signal or an image signal is received. If the bandwidth of the component is infinite, the frequency pull-in range of the AFC circuit of the present invention is -∞ to + ∞.

Example 2. FIG. 4 shows an embodiment corresponding to claim 2. In FIG. 4, 21 is a level detection circuit, 22 is a comparator, 23 is a voltage generation circuit, 2
Reference numeral 4 is an adder circuit, and 12b is an AFC circuit. The same reference numerals as those in FIG. 1 indicate the same or corresponding components.

The operation will be described. In the AFC circuit 12b, the real signal is frequency / voltage converted by the frequency discriminator 9, and after the error signal is detected by the differential amplifier 10, it is fed back to the local light source through the loop filter 11. On the other hand, the level detection circuit 21 detects the signal level of the image signal path, and if it is above a certain level, the comparator 2
2 outputs the detection signal HI. This makes it possible to know whether the intermediate frequency signal being received is a real signal or an image signal. If there is a detection signal HI, it is determined to be an image signal, and conversely, if there is no detection signal and is LO, it is determined to be a real signal. The voltage generation circuit receives the HI signal from the comparator 23 and generates a certain voltage. This voltage is set to a voltage that shifts the oscillation frequency of the local light source to a higher value by a certain constant value. In other words, this AF
If the received signal is a real signal, the C circuit executes the control as it is, and if it is an image signal, it is moved so that the frequency of the local oscillation light comes to the real side, and then AFC is performed. Therefore, the intermediate frequency is always locked at the point A in FIG. 3 (a). If the bandwidth of the components is infinite, the frequency pull-in range of the AFC circuit of the present invention is -∞ ~
It becomes + ∞.

Example 3. FIG. 5 shows an embodiment for claim 3. In the figure, 31 is an input terminal, 32
Is an output terminal, 37 is a four-branch circuit, 34a and 34b are delay lines, and 35a and 35b are double balanced mixers.
38 is an inverting circuit, 39 is a weighting circuit, 40 is an adding circuit, 41 is an amplitude limiting circuit, and 36 is a low-pass filter similar to the conventional example shown in FIG. Further, for convenience, the upper half portion 42a surrounded by the dotted line is referred to as a first differential detection circuit, and the lower half portion 42b is also referred to as a second differential detection circuit.

The object of the present invention is to provide a frequency discriminator having ideal characteristics as shown in FIG. 9 (a). It has been mathematically proved that such frequency characteristics can be expanded by a Fourier series only with an even function or only with an odd function. The principle of the present invention is to obtain a frequency discriminator close to an ideal characteristic by adding a delay detector corresponding to each term of the Fourier series. At this time, the delay time of each delay detector is represented by τ1, τ2, ..., τN (τ1 <τ2 <... <τN), and each of them is approximately τk = (2k-1) τ1 (k is 2 or more). Integer) or τk = 2 (k-1) τ1 (k is an integer of 2 or more).

The operation will be described below. The intermediate frequency signal input from the input terminal 31 is distributed to the first differential detection circuit 42a and the second differential detection circuit 42b by the 4-branch circuit 37. When the delay times τa and τb of the delay lines 34a and 34b are expressed by the following equations (6) and (7), τa = 1 / fc (6) τb = 1 / 3fc (7) The first differential detection circuit 42a and the 2 differential detection circuit 4
The output voltages Va (f) and Vb (f) of 2b are given by the following equations (8) and (9). Va (f) = Vo cos ωτa (8) Vb (f) = Vo cosωτb (9) The respective frequency characteristics are as shown in FIGS. 6 (a) and 6 (b). This figure is drawn such that the output voltage becomes 0 near DC in consideration of the fact that a normal differential detection circuit has no gain at DC. The inverting circuit 36 inverts the sign of the input voltage, as shown in FIG.

The weighting circuit 39 outputs, for example, three times the input voltage, as shown in FIG. 6 (b). In that case, the output voltage Vadd of the adder circuit 40
(F) is the value of expression (10). Vadd (f) =-Vo cos .omega..tau.a + 3 Vo cos .omega..tau.b (10) Then, the frequency characteristic is as shown in FIG. 6 (c). Assuming that the amplitude limiting circuit circuit 41 at the final stage limits a voltage of ± v or more, the frequency characteristic of its output is as shown in FIG. 6 (d). That is, in the frequency discriminator of the present invention, 3fc / 4
A highly sensitive characteristic with a steep slope in the vicinity can be obtained. How much higher sensitivity can be achieved is calculated below. First, the sensitivity of only the second differential detection circuit 42b is Vb.
The gradient of (f) at a frequency of 3fc / 4 is expressed as in the following equation (11). The sensitivity of the differential detection circuit as a whole is expressed by equation (12).

[0025]

[Equation 1]

From equations (11) and (12), it can be seen that the frequency discriminator of the present invention can realize a sensitivity increase of 4/3 times. If the frequency response of the components of the frequency discriminator of the present invention is infinite, the frequency pull-in range of the frequency discriminator of the present invention is 0 to 2 fc [Hz].

[0027]

As described above, according to the present invention, a frequency discriminator for a real signal and a frequency discriminator for an image signal is provided in a heterodyne receiver, and the frequency is controlled by its differential output. Since the level detector for the image signal is provided and the control frequency is shifted when it is determined that the image signal is being received, there is an effect that the oscillation frequency can be pulled in over a wide frequency range. Also, as a frequency discriminator, a plurality of partially weighted differential detectors are provided, and the delay time relations of only even functions or odd functions are provided, so that there is an effect of tuning with high sensitivity even if the pull-in frequency range is wide. is there.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is light 90 ° used in Examples 1 and 2;
It is a detailed view of a hybrid.

FIG. 3 is a diagram for explaining the operation of the first embodiment of frequency /
It is an output voltage relationship diagram.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

FIG. 5 is a frequency discriminator configuration diagram showing a third embodiment of the present invention.

FIG. 6 is a frequency / output voltage relationship diagram illustrating the operation of the third embodiment.

FIG. 7 is a block diagram of a conventional heterodyne receiver.

FIG. 8 is a block diagram of a conventional frequency discriminator.

9 is a diagram for explaining the operation of the conventional heterodyne receiver of FIG.

FIG. 10 is a diagram illustrating a relationship between an oscillation frequency and a received wave.

[Explanation of symbols]

 1 signal light 2 local light emission 3 local light source 5, 5a, 5b balanced light receiver 9, 9a, 9b frequency discriminator 10, 10a differential amplifier 11 loop filter 12, 12a, 12b AFC circuit 17 image rejection receiver circuit 21 level Detection circuit 22 Comparator 23 Voltage generation circuit 24 Addition circuit 33 Two branch circuit 34, 34a, 34b Delay line 35, 35a, 35b Double balanced mixer 37 Four branch circuit 38 Inversion circuit 39 Weighting circuit 40 Addition circuit 41 Amplitude limiting circuit 42a No. 1 differential detection circuit 42b 2nd differential detection circuit 54 3dB coupler 55a, 55b Polarization splitter

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[Procedure amendment]

[Submission date] April 14, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

Intermediate frequency signal is 3fc In the vicinity of / 4 [Hz] , the intermediate frequency is 3fc / 4 [H] indicated by the point A1.
z], the AFC circuit operates. Figure 9
In the case of (b), the frequency pull-in range of the frequency discriminator is ± f
c / 2 [Hz], the frequency pull-in range of the frequency discriminator in the case of FIG. 9C is ± 3fc / 2 [Hz]. However, since the output voltage characteristics of the frequency discriminator of FIG. 9 (b) and the frequency discriminator of FIG. 9 (c) are opposite to each other, the input to the differential amplifier 10 is properly used for the positive phase / negative phase. There is a need.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010]

As described above, the laser diode, which is a local light source, has an extremely low oscillation frequency stability against temperature fluctuation and is an extremely unstable oscillator. An AFC circuit having a wide pull-in range is required for the receiver. If the characteristic of the frequency discriminator that determines the pull-in range of the AFC circuit is ideal as shown in FIG. 9 (a), the frequency pull-in range of the AFC circuit will be very wide. However, the frequency characteristic of the conventional frequency discriminator is as shown in FIG. 9 (b), and the frequency pull-in range is only ± fc / 2 [Hz]. If the delay time τ is reduced, the pull-in range can be expanded to ± 3fc / 2 [Hz] as shown in FIG. 9C, but the change of the output voltage with respect to the frequency change becomes small. That is, the sensitivity becomes poor. Therefore, the conventional AFC circuit has a problem that the frequency pull-in range cannot be expanded without deteriorating the sensitivity. Further, as described above, there is a problem that the tuning range is narrow and there is a possibility of locking at the wrong frequency.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

From equations (11) and (12), it can be seen that the frequency discriminator of the present invention can realize a sensitivity increase of 4/3 times. Further, assuming that the frequency response of the components of the frequency discriminator of the present invention is infinite, the frequency pull-in range of the frequency discriminator of the present invention is -3fc / 4 to + 9fc / 4.
Up to [Hz] .

Claims (3)

[Claims] 1. A heterodyne receiver including an automatic frequency control circuit (AFC), comprising: a first frequency discriminator for taking out a received signal; and a second frequency discriminator for taking out a signal having a phase different from that of the received signal. A heterodyne receiver comprising: a first frequency discriminator and means for performing AFC by a differential output of the second frequency discriminator. 2. A heterodyne receiver equipped with an automatic frequency control circuit (AFC), comprising: a first frequency discriminator for extracting a received signal; and a second frequency discriminator for extracting a signal having a phase different from that of the received signal. A detector that detects the output level of the second frequency discriminator, and moves the oscillation frequency of the AFC by a constant value when the detector detects that the output level of the second discriminator exceeds the set level. And a heterodyne receiver. 3. A heterodyne receiver provided with an automatic frequency control circuit (AFC), comprising a frequency discriminator for extracting a signal for AFC, and having a plurality of delay time relations of only even functions or odd functions as its constitution. A frequency discriminator composed of a plurality of delay detectors, a weighting circuit provided in some of the delay detectors, and an adder for adding the outputs of the plurality of delay detectors including the weighted outputs. A heterodyne receiver characterized by being a receiver.