JPH0734549B2 - Receiver - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving device that can be used in a satellite broadcast receiver, a satellite communication device and the like.

2. Description of the Related Art Conventionally, FM signals have been used as signals for satellite broadcasting and satellite communications. Therefore, receivers for satellite broadcasting and satellite communications have used phase-locked demodulators to receive incoming weak signals with high sensitivity. However, in the case of a signal close to the saturation level such as a color bar signal, the threshold level can only be improved by 1 to 2 dB due to the relationship of the modulation specifications of the FM signal.
In this regard, new technology was needed. This is described in, for example, "Nio et al., Present state of satellite broadcasting home receivers, Journal of the Television Society of Japan: vol 38 No. 10." In addition, a variable frequency filter (tracking filter) or a frequency conversion device was connected in front of the phase-locked demodulator to improve the carrier-to-noise ratio of the input signal to achieve high sensitivity. For example, see “J. Clapper et al .: Phase-Locked and Frequency-Feedback System; Academic Press, 1972.
(J. Klapper, et al: Phase-Looked and Frequency-Feed
back Systems; ACADEMIC PRESS, 1972) ”.
Hereinafter, the above-described conventional receiving device will be described with reference to the drawings. FIG. 2 is a circuit block diagram of a conventional receiver, in which an FM signal input from terminal 1 has a tracking bandpass filter (hereinafter referred to as tracking bandpass filter) having a passband width narrower than an occupied frequency bandwidth determined by its frequency deviation. After passing through BPF (abbreviated as BPF) 2, the gain controller 3 is entered, the signal strength is optimized for demodulation, and then the phase comparator 4 is entered. A part of the signal from the output of the gain controller 3 is input to the detector 8 to be converted into a direct current component corresponding to the signal strength, and then input to the gain control drive circuit 9 to be input to the gain controller 3
Negative feedback is applied so that the output signal strength of is constant.
The oscillating signal of the oscillator 7 is input to the phase comparator 4 to compare the phase with the FM signal. The output signal corresponding to the phase difference is input to the DC amplifier 5, amplified, and then enters the loop filter (hereinafter referred to as LPF) 6, and its output enters the oscillator 7 and the phase of the oscillation signal of the oscillator 7 is changed to the phase of the FM signal. Sync to. The output from LPF6 passes through de-emphasis 12 and is output from terminal 13. A part of the output of the LPF6 is BP.
It is supplied via F11 to the drive circuit 10 that varies the center frequency of the tracking BPF2. This center frequency is synchronized with the instantaneous frequency of the FM signal input to the terminal 1, the frequency deviation does not change, and only the noise power is reduced, improving the threshold peculiar to the FM signal.

Problems to be Solved by the Invention However, in the configuration as described above, the gain control detector operates to detect the DC component, so the gain control does not follow at high speed. The input signal strength of the phase comparator changes, the loop gain of the phase-locked demodulator (hereinafter referred to as the PLL demodulator) changes, and the out-of-phase increases, which deteriorates the threshold level.

The present invention has been made in view of the above problems, and has a synchronization range expansion type PLL demodulator for expanding a synchronization range and a tracking B.
The object is to provide a receiving device with an improved threshold level in combination with a PF.

Means for Solving the Problems In order to solve the above problems, the receiving apparatus of the present invention detects the synchronization state of a synchronization range extension type PLL demodulator having two phase comparators and extending the synchronization range. FM that enters the phase comparator with high speed and accurate gain control by using a part of the output of the phase comparator as a drive signal for the gain controller.
Keeps the signal strength constant and controls the bandwidth of the tracking BPF connected to the input of the PLL demodulator to narrow the tracking BPF bandwidth and increase the carrier-to-noise ratio as the phase difference of the PLF increases. Then, it has a configuration for improving the threshold level.

Action The present invention makes it possible to improve the threshold level by making the input signal strength to the PLL demodulator constant and varying the bandwidth of the tracking BPF connected to the input by the above-mentioned configuration.

Embodiment Hereinafter, a receiver according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a circuit block diagram of a receiver in an embodiment of the present invention. The FM signal input from terminal 1 passes through the tracking BPF 2 to reduce the noise power without changing the frequency deviation and improve the carrier to noise power ratio. Further, the input signal that has passed through the tracking BPF2 enters the gain controller 3 for correcting the attenuation due to the tracking BPF2 and keeping the input signal strength to the phase comparators 4 and 17 constant. After that, the phase comparators 4 and 17 are entered. On the other hand, an oscillation signal is input from the oscillator 7 to the phase comparator 4, and the phase difference between the two signals becomes an output signal and enters the DC amplifier 5. Further, a part of the oscillation signal of the oscillator 7 is input to the phase comparator 17 via the π / 2 phase shifter 15, and when the phase synchronization is established by the loop of the phase comparator 4, the input FM signal And the oscillation signal are synchronized with each other to perform synchronous detection. The output signal is amplified to a predetermined size by the DC amplifier 16, enters the divider 14, calculates the ratio between the output signal output from the DC amplifier 5 and the DC amplifier 16, and supplies the result to the LPF 6. The phase comparator 4 and the phase comparator 17 are in an orthogonal relationship with each other, and as a result of being calculated by the divider 14, the characteristic of the phase comparator becomes a tangent function. Further LP
In F6, the bandwidth is limited to the bandwidth required to stabilize the loop and is supplied to the oscillator 7. This improves the threshold level. On the other hand, a part of the output signal from the LPF 6 is output as a demodulation signal from the terminal 13 via the de-emphasis 12. Further, a part of the output signal from the LPF 6 enters the center frequency control circuit 10 via the BPF 11, and changes the center frequency of the tracking BPF 2 in synchronization with the frequency deviation of the input FM signal to reduce the noise power. Further, a part of the output signal of the phase comparator 17 is input to the gain control drive circuit 9 to obtain a DC voltage or a DC current according to the input signal strength of the phase comparator 17, and the DC voltage or DC current is supplied to the gain controller 3. Then, the input signal is supplied to the phase comparators 4 and 17 with constant power to make the loop gain constant and the phase synchronization stable, thereby improving the threshold level.

EFFECTS OF THE INVENTION As will be apparent from the above description, the present invention is based on the bandwidth of the tracking BPF in which the output signal of one phase comparator of the synchronization range expansion type PLL demodulator is connected to the signal for gain control and the input side. By using it as a signal to change the phase synchronization state, the attenuation due to the tracking BPF2 is corrected while detecting the phase synchronization state, the input signal strength to the phase comparator is made constant, and the phase synchronization is stabilized, and the bandwidth of the tracking BPF is It is possible to provide a receiving device that optimizes and improves the threshold level.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a receiver of the present invention, and FIG. 2 is a circuit block diagram of a conventional receiver. 2 ... Tracking BPF, 3 ... Gain controller, 4 ... Phase comparator, 5 ... DC amplifier, 6 ... LPF, 7 ... Oscillator, 9 ... Gain control drive circuit, 10 ... Center frequency control Circuit, 11 …… BPF, 12 …… de-emphasis, 14 …… divider, 15 …… π / 2 phase shifter, 16 …… DC amplifier, 17 …… phase comparator, 18 …… bandwidth control circuit.

Claims (1)

[Claims] Claim: What is claimed is: 1. A phase-locked demodulator for an FM signal, which comprises a first and second phase comparators, a DC amplifier, a loop filter, a divider and an oscillator, via a variable frequency narrow band filter and a gain controller. When inputting to and demodulating, the center frequency of the variable frequency narrow band filter is changed by a part of the demodulated signal, and the operation is performed to follow the frequency change of the input signal, and the synchronization state of the phase-locked demodulator A part of the output of the second phase comparator that performs a synchronous detection operation to detect the signal is used as a drive signal for the gain controller that changes the input signal strength to the first and second phase comparators, and The receiving device, wherein a part of the output of the second phase comparator is used as a drive signal for changing the bandwidth of the variable frequency narrow band filter.