CN2807615Y

CN2807615Y - Heterodyne AM synchronous demodulation aural receiver

Info

Publication number: CN2807615Y
Application number: CN 200520071851
Authority: CN
Inventors: 朱自付
Original assignee: Nanjing Panda Electronics Co Ltd; Panda Electronics Group Co Ltd
Current assignee: Nanjing Panda Electronics Co Ltd; Panda Electronics Group Co Ltd
Priority date: 2005-05-27
Filing date: 2005-05-27
Publication date: 2006-08-16
Anticipated expiration: 2015-05-27

Abstract

The utility model relates to a heterodyne AM synchronous demodulation broadcasting receiver which is composed of a tuning circuit, a frequency converting circuit, an intermediate frequency phase-lock loop, a double balanced mixer, an audio frequency filter circuit and an audio frequency power amplifying circuit, wherein the tuning circuit is the input oscillating circuit and the receiving circuit double tuning circuit of a tuning mixer; signals with 450 khz intermediate frequency can be generated by the tuning circuit, when the tuning circuit works, frequency mixing is carried out between replicated intermediate carrier signals and intermediate frequency signals of a receiver, and after the frequency mixing is carried out, AM audio signals are outputted to an intermediate frequency amplifier TR2 which amplifies 450 khz intermediate frequency. Amplified intermediate frequency signals are connected with the phase-lock loop, and audio signals are separated out and are outputted from the phase locked loop. Outputted and demodulated audio signals pass through a low pass filter, and are outputted by the audio frequency power amplifying circuit. The demodulation distortion problem does not exist in the utility model.

Description

Heterodyne system AM synchronous demodulation broadcasting receiver

One, technical field:

The utility model relates to a kind of AM broadcasting receiver, especially heterodyne system AM synchronous demodulation broadcasting receiver.

Two, background technology:

The AM broadcast technology is apart from existing last 100 years history of the present.Since FM broadcasting has been arranged, as if AM broadcasting treated coldly, people pour into frequency modulation or FM stereophonic broadcast, television broadcasting one after another, add nowadays CD audio and MP3, MP4 have been arranged, the city young man is especially away from AM broadcasting, AM broadcasting listener group has also lacked much really, young man advocates digital product, leader's fashion is modish, the most loyal audience is no more than city the elderly and vast rural area audience, what these audiences paid close attention to is to listen to valuable information, as news, weather forecast and various health care lectures etc., not too how lies in tonequality.That what reason people no longer is ready to pay close attention to AM broadcasting so on earth? analyze from the angle of technology, AM broadcasting exists the large-signal demodulation distortion excessive and be vulnerable to the deficiency of noise interference really, the large-signal distortion seriously mainly is to have adopted diode demodulation (being envelope detection), be subject to disturb is that the AM modulation system determines, many interference sources have the amplitude modulation feature, for example around you, there is the people using power consumption equipment, as electric drill or unlatching fluorescent lamp, automobile engine etc., just can produce " whistling; " in the AM broadcast receiver sound, if on the occasion of thunderstorm season, between cloud layer that it is aerial and the cloud layer or the discharge between cloud layer and the earth, the capital is swarmed in the middle of the AM broadcast receiver, and the sensitivity height of healing is subjected to annoyance level more serious.Usually the spectrum distribution of thunder and lightning is very wide, from the hundreds of hertz to the number megahertzes, because the thunder and lightning energy mainly concentrates near the 20kHz myriametric wave wave band, to the myriametric wave communication influence greatly, broadcasting has appreciable impact to AM, thundery sky is listened to the radio programme, and the broadcast receiver loud speaker transmits random " loud, high-pitched sound " sound frequently and makes one nervous, and Here it is thunder and lightning is to the characteristic feature of AM broadcasting receiver influence.Be thunder and lightning equally, the influence of its frequency-modulation broadcasting is minimum, at first is that the standard of frequency modulation is different with the AM mode, and FM receiver is difficult for disturbed, secondly is exactly that the thunder and lightning energy does not arrive so high frequency.

Be subject to interference and large-signal demodulation distortion and so on problem and adopt the phase-locked loop combined synchronous demodulation technique better to solve, tonequality obtains obvious improvement, from overall Auditory estimating, reached a new step, but a fact that it must be admitted that, its range scope can't reach the broadness of frequency modulation (FM) broadcasting forever.

Three, summary of the invention:

The purpose of this utility model is: solve AM large-signal demodulation distortion problem and be subject to the deficiency of noise interference.Except that combined synchronous demodulation technique is adopted in demodulation, also the intermediate frequency loop is also adjusted accordingly, single tuning is changed into double tunning.

The utility model purpose is achieved in that heterodyne system AM synchronous demodulation broadcasting receiver, partly is made up of resonant tank, frequency changer circuit, IR-PLL road, double balanced mixer, audio frequency filter circuit and audio power amplifier circuit etc.Tuning circuit is the input oscillating circuit and the receiving circuit double-tuned circuit of tuning frequency mixer, produce intermediate frequency 450kHz signal, intercarrier signal of duplicating during work and receiver intermediate-freuqncy signal are carried out mixing, the intermediate frequency amplifier TR2 that after the mixing AM audio signal output is extremely amplified the 450kHz intermediate frequency, amplified IF signal connects phase-locked loop, carry out the synchronized orthogonal detection, comprise the 90 degree phase-shift circuits that trigger U1 constitutes, electronic switch U2, swing to integrated circuit U3 and constitute phase-locked loop, isolating audio signal exports from phase-locked loop, the low pass filter that the audio signal of output after the demodulation constitutes through operational amplifier U4, and export by audio power amplifier circuit U5.

Described resonant tank is a double tuned circuit.

Intermediate frequency amplifier TR2 is the intermediate frequency amplifier of 450kHz.

Characteristics of the present utility model are: listen to AM broadcasting with such covering device, can stay fresh and new sensation to the people, the Auditory estimating conclusion is: the high pitch part is limpid, bright, bass part is totally strong, various noises interference have also been lacked many, its tonequality, music level and dynamic range almost can compare favourably with early stage valve radio set, this a collection of just AM listens to yearning that the fan pursues, along with science and technology is constantly progressive, especially the appearance of some new units, traditional AM tonequality can improve, improve.If adopt the diode detection circuit, be certain to bring because the nonlinear distortion that non-linear device produced, distortion level is normally (is sustainable to tonequality in the less demanding age at that) between 0.5%～20%, go up the diode detection circuit in case use, distortion phenomenon just can't be avoided.The maximum characteristics of the utility model are not have the demodulation distortion problem, according to years of researches and Technical Follow-Up, domestic still do not have this product at present and come out, and this technology can spread in the middle of the civilian even high-grade automobile audio in the future, realizes that multiband also will be a lead-pipe cinch.

Four, description of drawings

Fig. 1 is the utility model block diagram

Fig. 2 is the utility model circuit diagram

Five, embodiment:

As shown in the figure, this receiver mainly partly is made up of resonant tank, frequency changer circuit, IR-PLL road, double balanced mixer, audio frequency filter circuit and audio power amplifier circuit etc.TR1 is a mixting circuit, high-frequency signal that receives and local oscillator mixing, difference go out or and go out a stable 450kHz intermediate-freuqncy signal, intercarrier signal of duplicating during work and receiver intermediate-freuqncy signal are carried out mixing, the AM audio signal can be taken out after the mixing, intermediate frequency amplifier TR2 amplifies the 450kHz intermediate frequency, amplified IF signal is sent to phase-locked loop, carry out the synchronized orthogonal detection, comprise the 90 degree phase-shift circuits that trigger U1 constitutes, electronic switch U2, swing to integrated circuit U3 and constitute phase-locked loop, isolate audio signal, audio frequency after the demodulation must increase corresponding low pass filter not needing composition to filter out, operational amplifier U4 is a low pass filter, and U5 is an audio power amplifier circuit.

Circuit block diagram such as Fig. 1, electrical schematic diagram is seen Fig. 2.This exemplary electrical circuit is an AM medium wave receiving circuit, and receive frequency range is: 535～1605kHz.Heterodyne system AM synchronous demodulation receiver is much better than direct amplifier system on indexs such as sensitivity and selectivity, need not can receive by antenna.

Operation principle is as follows: the AM broadcast singal is coupled to L2 by antenna coupling coil L1, L1 is a primary coil, L2 is a secondary coil, L2 is sent to frequency changer circuit TR1 with high-frequency signal, extraneous signal produces a fixing intermediate frequency after the frequency changer circuit frequency conversion, this new intermediate frequency is neither domestic 465kHz, 455kHz that neither south east asia, but 450kHz, to subordinate's intermediate frequency amplifier circuit, for obtaining best sensitivity and selectivity, the intermediate frequency coupling transformer does not re-use single-tunded circuit to this intermediate frequency by the TR1 collector coupled, adopt double-tuned circuit that intermediate-frequency bandwidth is further widened with foot, this to improve selectivity overcome crosstalk helpful.It is that the 450kHz intermediate frequency is amplified (if intermediate-frequency gain also can be appended one-level or secondary inadequately) that TR2 mainly acts on, and amplified IF signal is sent to phase-locked loop.The purpose of selecting intermediate frequency 450kHz for use be for future digital product provide convenience, making each stepping of tuner is 9kHz, 9kHz just in time is the AM channel width that International Telecommunications Union organizes defined, each stepping is 9kHz, can just be eliminated by 450kHz, 465kHz or 455kHz then can't eliminate, and can be eliminated to mean that all AM broadcasting stations can both receive in certain zone.

The effect of double balanced modulator is, it can duplicate intermediate frequency 450kHz signal, intercarrier signal of duplicating during work and receiver intermediate-freuqncy signal are carried out mixing, the AM audio signal can be taken out after the mixing, the intercarrier signal that phase-locked loop duplicates must be in full accord with the frequency and the phase place of intermediate frequency carrier, only under on all four prerequisite, could carry out mixing to its intermediate frequency, just can isolate audio signal at last, audio signal after the demodulation must increase corresponding low pass filter not needing composition to filter out, obtain that we want, pure AM audio signal, last pure audio signal is carried out power amplification by U5, until promoting a loud speaker pronunciation.Use the AM demodulator circuit of phase-locked loop, demodulation distortion exists hardly, and the large-signal demodulation is still like this.

Claims

1, heterodyne system AM synchronous demodulation broadcasting receiver, by resonant tank, frequency changer circuit, the IR-PLL road, double balanced mixer, audio frequency filter circuit and audio power amplifier circuit are formed, it is characterized in that tuning circuit is the input oscillating circuit and the receiving circuit double-tuned circuit of tuning frequency mixer, produce intermediate frequency 450kHz signal, intercarrier signal of duplicating during work and receiver intermediate-freuqncy signal are carried out mixing, the intermediate frequency amplifier (TR2) that after the mixing AM audio signal output is extremely amplified the 450kHz intermediate frequency, amplified IF signal connects phase-locked loop, carry out the synchronized orthogonal detection, 90 degree phase-shift circuits by trigger (U1) formation, electronic switch (U2), swing to integrated circuit (U3) and constitute phase-locked loop, isolating audio signal exports from phase-locked loop, the low pass filter that the audio signal of output after the demodulation constitutes through operational amplifier (U4), and export by audio power amplifier circuit (U5).

2,, it is characterized in that intermediate frequency amplifier TR2 is the intermediate frequency amplifier of 450kHz by the described heterodyne system AM of claim 1 synchronous demodulation broadcasting receiver.