JPH04127608A - Sweep afc circuit - Google Patents

Abstract

PURPOSE:To take correct synchronization by providing an amplitude detection circuit, a means deciding the location of a reference pilot carrier, and a means applying a prescribed control voltage to a voltage controlled oscillator to the AFC circuit. CONSTITUTION:While a control voltage fed to a voltage controlled oscillator 8 is being swept, an output of a band pass filter 7 is detected by an amplitude detection circuit (VCO) 111 and a position of a reference pilot carrier is decided from the detection output voltage and a prescribed control voltage is applied to the voltage controlled oscillator 8 based on the decided position information. Thus, even when the frequency stability of the VCO 111 is not excellent, the reference pilot carrier is searched and judged and correct synchronization is taken.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides an AFC that achieves frequency synchronization by selectively extracting a reference pilot carrier from received waves that have undergone frequency fluctuations.
This invention relates to a sweep AFC circuit when searching for a pilot wave in an automatic frequency control circuit.

(Prior Art) Conventionally, a sweep AFC circuit has been configured as shown in FIG.

In Figure 3, 1 is a received wave input terminal, 2 is a mixer, 3 is an output terminal, 4 is a narrowband BPF (band pass filter), 5
is a pilot reference oscillator, 6 is a phase comparator, 61 is a phase comparison output, 62 is a phase lock detection output, 7 is a loop filter, 8 is a voltage controlled oscillator (hereinafter referred to as VCO), 9
is a sweep wave generation type, ]0 is a sweep control circuit, and 12 is a sweep switching circuit.

According to this conventional circuit, in the initial state where the output terminal of the narrowband BPF 4 cannot selectively extract the reference pi 0.7 carrier in the received signal, it is natural that the mixer 2,
A P comprising a narrowband BPF 4, a phase comparator 6, a loop filter 7, a sweep switching circuit] 2, and a voltage controlled oscillator 8.
The LL circuit cannot be locked, and the phase lock detection output 62 is in an unlocked state, so that the sweep control circuit 10
The sweep wave from the sweep wave generator 9 is selected by switching the sweep switching circuit 12 under the control of the wave generator 9 . This sweep wave causes VCO8 to slowly change the frequency,
The mixer 2 slowly searches the received signal for a pilot wave using the narrowband BPF 4 bandwidth.

During the search, when a reference pilot carrier in the received signal is selected and extracted at the output terminal of the narrowband BPF 4,
The phase difference with the pilot signal output from the pilot reference oscillator 5 becomes the same, a lock detection state is entered, and a phase lock detection output 62 is output from the digit comparator 6. This phase lock detection output 62 is transmitted to the sweep control circuit 10.
This causes the sweep switching circuit 12 to be switched and the sweep wave from the sweep wave generator 9 to be stopped.

As described above, the sweep AFC circuit selects and extracts a reference pilot carrier from among the received waves by a sweep search operation, performs PLL synchronization, corrects the received wave that has undergone frequency fluctuation, and generates the corrected received wave. is output from output terminal 3.

However, in the above-mentioned conventional circuit, ■Since the frequency stability of CO8 is generally not good, the sweep width during frequency search changes due to temperature fluctuations, etc., and the carrier adjacent to the reference pilot carrier is connected to the output terminal of narrowband BPF4. However, there was a problem in which the carrier was incorrectly synchronized with the adjacent carrier.

On the other hand, if the sweep width was designed to be small in consideration of the frequency fluctuations of the VCO 8, it would not be possible to cover the fluctuations in the input frequency, resulting in a problem that synchronization with the reference pilot carrier could not be achieved.

(Problems to be Solved by the Invention) As mentioned above, in conventional sweep AFC circuits, the stability of the voltage controlled oscillator is generally poor, resulting in incorrect synchronization with adjacent carriers or failure to synchronize with the reference pilot carrier. There was a problem.

Therefore, the present invention was made in view of these conventional problems, and it is a sweep method that can determine the frequency stability of a voltage controlled oscillator or, at worst, search for a reference pilot carrier and achieve correct synchronization. The purpose is to provide an AFC circuit.

[Structure of the Invention] (Means for Solving the Problems) A PLL circuit including a band pass filter, a pilot reference oscillator, a phase comparator, a loop filter, a voltage controlled oscillator, and a mixer, In a sweep AFC circuit that sweeps a control voltage applied to the voltage controlled oscillator during an unlocked state and synchronizes a reference pilot carrier extracted from a reception frequency by the bandpass filter with the oscillation frequency of the pilot reference oscillator, the voltage control an amplitude detection circuit that detects the output of the band-pass filter while sweeping a control voltage applied to the oscillator; a means for determining the position of the reference pilot carrier from the detected output voltage of the amplitude detection circuit; and the position information. and means for applying a predetermined control voltage to the voltage controlled oscillator based on.

(Function) In the sweep AFC circuit of the present invention, while sweeping the control voltage applied to the voltage controlled oscillator, the output of the band pass filter is detected by an amplitude detection circuit, and from this detected output voltage, the reference pilot carrier is detected. The position is determined, and a predetermined control voltage is applied to the voltage controlled oscillator based on the determined position information.

(Embodiment) Hereinafter, an embodiment of the sweep AFC circuit of the present invention will be described with reference to the accompanying drawings.

In Figure 1, 1 is a received wave input terminal, 2 is a mixer, and 3
is an output terminal, 4 is a narrow band BPF, 5 is a Nonoirot reference oscillator, 6 is a phase comparator, 61 is a phase comparison output, 62 is a phase lock detection output, 7 is a loop filter, 8 is a voltage controlled oscillator (hereinafter referred to as 11 is an AFC sweep/judgment section, 11 is an amplitude detection circuit, 112 is a CPU circuit, and 12 is a sweep switching circuit.

Below, the configuration of an embodiment of the sweep AFC circuit of the present invention,
The operation will be explained in detail.

First, in the initial state where the reference pilot carrier has not been selectively extracted from the output terminal of the narrowband BPF 4, the mixer 2, narrowband BPF 4, phase comparator 6, loop filter 7, sweep switching circuit 12, voltage controlled oscillator 8 The PLL that is equipped with this becomes unlocked and cannot be locked.
The phase lock detection output 62 from the phase comparator 6 is sent to the CPU 11.
2 is done manually. Then, the sweep switching circuit 12 is controlled by the control of the CPUI 12, and thereby,
Swive wave (second wave) output from CPU 1.1.2
Figure (C)) is selected, and this sweep wave causes VCO8
The control voltage applied to the signal sweeps, the VCO 8 slowly changes the frequency, and the mixer 2 slowly searches for an isolated carrier in the received signal using the bandwidth of the narrow BPF 4. During this search, the detection output of the amplitude detection circuit of the AFC sweep/judgment unit 11 connected to the output of the narrowband BPF becomes, for example, as shown in FIG. The analog detection voltage is taken into the CPU 112.

Various methods can be considered for software processing within the CPU, but in this embodiment, the differential absolute value of the detected voltage is taken to obtain a processed waveform as shown in FIG. 2(b). In this case, since the distance a - d is predetermined, the point P
C is the signal located at the reference pilot carrier.
It will determine if it is PU112.

After the above processing, the CPU 112 outputs the fixed control voltage VB (FIG. 2(C)) corresponding to the point P, and applies this fixed control voltage VB to the VCO 8 via the sweep switching circuit 2. In this way, when the reference pilot carrier in the received signal is selectively extracted to the output terminal of the narrowband BPF 4 by the sweep search operation and reference pilot carrier determination, the PLL locks and the phase lock detection output 62
is in a lock detection state, and the sweep switching circuit 12 is switched under the control of the CPUI 12 to select the output of the loop filter and maintain synchronization. As a result, the received wave that has undergone frequency fluctuation is corrected to the normal frequency, and the output terminal 3
It can be output from.

[Effects of the Invention] As explained above, in the sweep AFC circuit of the present invention, while sweeping the control voltage applied to the voltage controlled oscillator, the output horn of the bandpass filter is detected by the amplitude detection circuit, and the detected output is The position of the reference pilot carrier is determined from the voltage, and a predetermined control voltage is applied to the voltage controlled oscillator based on the determined position information.

Therefore, even if the frequency stability of vCO is poor, the reference pilot carrier wave can be searched and determined, and correct synchronization can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the sweep switching circuit of the present invention, FIGS. 2(a) to (c) are conceptual diagrams of the processing of the CPU according to FIG. 1, and FIG. 3 is a diagram of a conventional sweep AFC circuit. It is a block diagram. ]... Received wave input terminal, 2 mixer, 3. Output terminal, 4
...Narrowband BPF, 5...Pilot reference oscillator, 6
... Phase comparator, 61. Phase comparison output, 62.. Phase lock detection output, 7.. Loop filter, 8. Voltage controlled oscillator (VCO), 1.1.. AFC sweep/judgment section, ]1 ...amplitude detection circuit, 112...CPU circuit,
12 Swive switching circuit.

Claims (1)

[Scope of Claims] A PLL circuit having a bandpass filter, a pilot reference oscillator, a phase comparator, a loop filter, a voltage controlled oscillator, and a mixer; In a sweep AFC circuit that sweeps a control voltage applied to a controlled oscillator and synchronizes a reference pilot carrier extracted from a reception frequency by the bandpass filter with an oscillation frequency of the pilot reference oscillator, the control voltage applied to the voltage controlled oscillator is swept. an amplitude detection circuit for detecting the output of the bandpass filter; means for determining the position of the reference pilot carrier from the detected output voltage of the amplitude detection circuit; and means for determining the position of the reference pilot carrier based on the position information; A sweep AFC circuit comprising means for applying a predetermined control voltage.