CN2106449U

CN2106449U - Float carrier amplitude modulation device

Info

Publication number: CN2106449U
Application number: CN 91232464
Authority: CN
Inventors: 董振平; 智均平
Original assignee: RADIO TV BUREAU PREFECTURE ADMINISTRATIVE OFFICE HEBEI PROV
Current assignee: RADIO TV BUREAU PREFECTURE ADMINISTRATIVE OFFICE HEBEI PROV
Priority date: 1991-12-19
Filing date: 1991-12-19
Publication date: 1992-06-03

Abstract

The utility model discloses an amplitude modulation device. The device is a passage which can be connected in a series feed pulse width modulation transmitter and can generate carrier wave controlled signals. The utility model is composed of a full crest value rectifier, a time constant processing circuit, a summing amplifier and limiter branch, a low pass filter and summing amplifier branch, a comparative output unit, a dynamic compensator, a summing unit, an amplifier, etc. The dynamic compensator can generate compensating signals whose wave form is the same with the wave form of the feedback signal of the control signals, and whose phase is opposite to the phase of the feedback signal of the control signals, and then the influence caused by prime machine negative feedback to floating carrier wave control signals is counteracted. The utility model solves the problem that the carrier wave can not follow modulation signals transient peak level to change.

Description

Float carrier amplitude modulation device

The utility model relates to a kind of amplitude modulation means, and the amplitude of carrier frequency depends on the modulator of strength of modulating signal in specifically a kind of output.

AM broadcast transmitter adopts floating carrier amplitude modulation (DAM) mode, compares with the ordinary amplitude modulation mode, guaranteeing that sideband power is constant and broadcasting under the impregnable substantially situation of effect, can reduce the energy consumption of transmitter significantly.

Realized at present on series feed pulsewidth transmitter, inserting amplitude modulation apparatus with floating carrier, thus reach carrier wave along with the size of the dynamic peak level of audio signal modulation unsteady purpose.Concrete formation is that amplitude modulation apparatus with floating carrier is connected on the former machine audio frequency amplifier of series feed pulsewidth transmitter, be that audio signal is passed through the former machine audio frequency amplifier of fan-in, at audio signal input end and connect one tunnel passage that produces the carrier wave controlled signal, this passage is serially connected with the all-wave peak rectifier, time constant treatment circuit and signal processing circuit etc. are exported control signal in channel rear portion by amplifier.Signal processing circuit is for producing a kind of broken line type or saddle-shape, and perhaps both carrier wave controlled characteristic curves of having both at the same time so that audio modulation signal is controlled, reach purpose of energy saving.The floating carrier device of existing all kinds of floating carrier amplitude modulated transmitters, owing to be to be that input signal is adjusted circuit parameter according to exchanging steady-state signal, its carrier wave controlled characteristic curve can reach more satisfactory degree.But the waveform of a voice signal can be divided into initial, stable and finishes three sections processes from the angle of time duration, that is the envelope of signal can be divided into growths, stablizes and decay for three stages.According to statistics, the stable section of many sound is very short or does not have stable section that such voice signal then shows tangible transient response.Because the time-histories of voice signal has stable state and transient state two parts, the electroacoustic equipment that therefore transmits voice signal just must possess stable state and transient state requirement.And the floating carrier amplitude modulated transmitter also just must possess corresponding stable state and transient state requirement, utilize the test signal of analoging sound signal time-histories characteristics shown in Figure 1, existing floating carrier amplitude modulated transmitter is tested, with the broken line type characteristic curve is example, observe carrier envelope with oscilloscope, then demonstrate carrier wave controlled characteristic curve as shown in Figure 2.And when testing, can make as shown in Figure 3 desirable broken line type controllability Tequ line with trace-point method with sinusoidal steady-state signal.Comparison diagram 2, Fig. 3 as seen, when testing with transient signal, in ascent stage of modulation signal (t1) in the time, carrier voltage Uf can not float to 1(carrier voltage Uf and modulation signal voltage U on request _ΩBe normalized value), enter stable state section (t2) at modulation signal, carrier wave could float to 1 gradually.The transient response of clearly this floating carrier amplitude modulated transmitter is undesirable, can produce a large amount of ovennodulation in actual broadcast, and the tonequality of receiving terminal is degenerated.The generation of this problem, its root are caused by the degenerative influence of former machine.In common pulsewidth transmitter, the envelope negative feedback is an audio signal, and the audio frequency negative feedback is audio signal and fixing direct voltage sum.At audio input end,, all adopt resaistance-capacity coupling circuit in order to intercept the direct current composition in the negative-feedback signal.In floating carrier pulsewidth transmitter, the envelope negative-feedback signal is the stack of audio signal and floating carrier amplitude modulation (DAM) control signal, the audio frequency negative-feedback signal is audio signal, DAM control signal and direct voltage three sum, the feedback network of audio input end to the transmission coefficient of DAM signal with the same to the transmission of audio signals coefficient be a constant.But the DAM control signal is superimposed at the input of comparator and its feedback signal.The time-histories characteristics of DAM control signal are to be one to have the fluctuation signal of direct current composition as a rule, so the feedback signal of DAM can not be passed through coupling circuit undistortedly.That is the transmission coefficient that arrives comparator input terminal is constant no longer, and becomes a variable.So just cause carrier wave not float by original control signal, signal rises fast more, and the amplitude of influence is big more, promptly produces effect shown in Figure 2.Carrier wave does not catch up with when therefore causing audio frequency signal amplitude to increase, and produces toning, causes tonequality to descend and the outer emission of band (being distortion).

Second problem that the floating carrier amplitude modulated transmitter exists is: opposite to the effect of carrier wave at descending branch (AB section) modulation signal of saddle type curve when carrier wave controlled characteristic curve is saddle type curve (Fig. 4) with control signal, i.e. and modulation signal voltage U _ΩBe increased to 0.15 during this period of time from 0, corresponding carrier voltage Uf reduces, and at this moment just can hear the unsteady additional interference that is produced of carrier wave at receiving terminal.This is because when the modulation signal changes in amplitude is very fast, and carrier wave changes also very fast, and the interference signal that additional modulation forms just has the frequency component in the transmitter band of falling into, thereby hears back drop.And carrier wave controlled characteristic curve is when being broken line type, because the change of carrier wave and the correlation of broadcast program modulation signal just be can't hear the unsteady additional interference that is produced of carrier wave at receiving terminal.

The purpose of this utility model is followed modulation signal transient peak level and is changed this problem with regard to providing a kind of carrier wave that fundamentally solves, eliminate the amplitude modulation apparatus with floating carrier of negative feedback to the influence of floating carrier control signal, this device also has and eliminates the characteristic descending branch of saddle-shape function to the adverse effect of transmitter generation when the modulation signal changes in amplitude is very fast simultaneously.

The utility model is achieved in that the input input at the former machine audio frequency amplifier of series feed pulse-width modulated transmitter has audio signal, at audio signal input end and connect one tunnel passage that produces the carrier wave controlled signal, this passage integral body is this amplitude modulation apparatus with floating carrier, wherein be serially connected with the all-wave peak rectifier, the time constant treatment circuit, at time constant treatment circuit rear portion and connect two branch roads, be serially connected with summing amplifier and amplitude limiter among the branch road A, be serially connected with low pass filter and summing amplifier among the branch road B, the output of two branch roads connects the comparison follower, the output that compares follower, be connected to the first input end of adder after one tunnel serial connection dynamics compensation circuits, be connected to second input of adder behind another road output serial connection amplifier, the output of adder is connected to another amplifier input terminal, and this amplifier is in the rear portion of this passage output control signal.At first, in this device, be to eliminate the influence of negative feedback, designed the back that dynamics compensation circuits is connected to the comparison follower the floating carrier control signal.This dynamics compensation circuits can produce the compensating signal that the feedback signal waveform shape is identical, phase place is opposite with control signal, with Steady-State Control signal stack back output, be sent to the comparator of pulse width modulator as the actual carrier controlled signal, thereby offset the influence of former machine negative feedback the floating carrier control signal.Secondly, serial connection one low pass filter in the branch road B of generation saddle-shape controlled characteristic curve descending branch makes carrier wave by the solid line among Fig. 4 unsteady (saddle-shape) when the modulation signal variation is slow like this; Rise when very fast at modulation signal, the dotted line that the carrier wave initial stage is pressed Fig. 4 floats, and carries out the transition to solid line part (being broken line type) then.The cut-off frequency design of low pass filter (is lower than 20Hz) outside transmitter band, the frequency component that also is about to the interference signal of additional modulation formation is discharged outside transmitter band, can listen the additional interference noise thereby avoided producing.

The utility model can also be realized like this: at the input of the audio frequency amplifier of series feed pulse-width modulated transmitter and connect one tunnel passage that produces the carrier wave controlled signal, this passage is serially connected with the all-wave peak rectifier, the time constant treatment circuit, behind the time constant treatment circuit and connect two branch roads, be serially connected with summing amplifier and amplitude limiter among the branch road A, be serially connected with low pass filter and summing amplifier among the branch road B, the output of two branch roads connects the comparison follower, relatively the output of follower is connected to the amplifier input terminal that is located at this channel rear portion, this amplifier output control signal.For eliminating the influence of negative feedback to the floating carrier control signal, change former machine audio frequency amplifier into the direct-current coupling amplifier, the ac-coupled circuit that also is about in the former machine feedback control loop changes DC coupling circuit into, and one direct reverse voltage is set to offset the direct current composition in the feedback signal at the input of audio frequency amplifier.After changing like this, producing mechanisms such as interior dynamics compensation circuits of carrier wave controlled signal passage and adder can save.The effect of the low pass filter in branch road B is still for eliminating the additional interference of saddle-shape characteristic.

Key of the present utility model is fundamentally to have solved carrier wave and follows modulation signal transient peak level and change this problem, the AC coupled that adopts dynamics compensation circuits or change in the former machine feedback loop is direct-current coupling, eliminated negative feedback that the DAM broadcast industry never recognizes for a long time influence to the floating carrier control signal, carrier wave does not catch up with when having avoided effectively increasing rapidly because of audio frequency signal amplitude, produces toning and makes degradation series of malpractice under the broadcast program tonequality.Installed low pass filter additional simultaneously before the circuit that produces saddle-shape characteristic curve descending branch, avoided the generation of additional interference, further improved broadcast program quality, energy-saving effect is also very remarkable.

Below in conjunction with accompanying drawing the utility model is further described.

Fig. 1 is the analoging sound signal of test DAM transmitter transient response.

Observe existing DAM carrier of transmitter controlled characteristic when above-mentioned analoging sound signal is imported with oscilloscope among Fig. 2.

Fig. 3 is a broken line type control characteristic of steady state curve.

Fig. 4 is a saddle-shape control characteristic of steady state curve.

Fig. 5, Fig. 6 are two kinds of implementation structured flowcharts of the present utility model.

Fig. 7 is circuit theory diagrams of the present utility model.

Fig. 8 is the circuit theory diagrams that audio frequency amplifier changes the direct-current coupling amplifier into.

Embodiment 1: in the structured flowchart of Fig. 5,1 is former machine audio frequency amplifier, and 2 is the all-wave peak rectifier, and 3 is the time constant treatment circuit, 4,7 is summing amplifier, 5 is amplitude limiter, and 6 is low pass filter, and 8 for comparing follower, 9 is dynamics compensation circuits, 10,12 is amplifier, and 11 is adder, and its concrete formation is seen Fig. 7.

In the formation of this amplitude modulation apparatus with floating carrier, each several part is with the manufacturing of universal circuit version basically.Wherein, all-wave peak rectifier 2 is based on two groups and the operational amplifier IC1, the IC2 that connect, be equipped with resistance R 1-R5, diode D1-D4 is formed by connecting, input signal is connected to the in-phase end of IC1 through resistance R 1, is connected to the inverting input of IC2 through resistance R 4, and time constant treatment circuit 3 is made up of time constant circuit and emitter follower two parts, the time constant treatment circuit is made up of resistance R 7, R8 and capacitor C 1, and emitter follower promptly is made of amplifier IC3.Summing amplifier 4 connects into amplifying circuit by operational amplifier IC4, resistance R 11-R16, potentiometer W3, and input signal is connected to the inverting input of IC4 through resistance R 9, and the DC level that is obtained by potentiometer W2 is connected to the in-phase input end of IC4 through resistance R 10.The version of summing amplifier 7 is consistent with the structure of summing amplifier 4.Amplitude limiter 5 is voltage stabilizing didoe D5, connects, between the output and ground wire of summing amplifier 4.Lowpass wave device 6 is connected and composed by operational amplifier IC5, resistance R 17-R19, capacitor C 2-C4, and input signal is connected to the in-phase input end of IC5.Relatively follower 8 is connected and composed by diode D6, D7 and resistance R 20.Dynamics compensation circuits 9 is by operational amplifier IC8, resistance R 32, R33, and capacitor C 5 and potentiometer W8 connect and compose, and input signal is connected to the in-phase input end of IC8.Amplifier 10 is connected by resistance R 29-R31 and amplifier IC7, constitutes homophase and amplifies.Adder 11 is by resistance R 34, R35 and connect and constitute, and the output of dynamics compensation circuits 9 meets R35 through potentiometer W8, and the output of amplifier 10 meets R34 through potentiometer W7.Amplifier 12 is connected by resistance R 36, R37 and amplifier IC9, constitutes homophase and amplifies.

Spontaneous emission machine limit is put the modulation signal U of output _ΩImport this device.U _ΩExport U1 behind all-wave peak rectifier 1 and time constant circuit, U1 is the direct current signal that the dynamic peak level of reflection modulation signal changes.This signal is divided into two branch roads after the emitter follower buffering.Branch road A is made up of gain summing amplifier 4 and amplitude limiter 5 easy to adjust, is used for forming the characteristic ascent stage.Behind amplitude limit, export U3.Regulate intercept and slope that W2 and W3 can change straight line.Branch road B is made up of low pass filter 6 and summing amplifier 7, is used for forming characteristic descending branch.Regulate intercept and slope that W4 and W5 can change straight line.K switch 1 is the broken line type characteristic when a of position, is the saddle-shape characteristic when b.The output U3 of two branch roads and U4 are through relatively exporting U5.U5 is divided into two branch roads, and one the tunnel is amplifier 10, and one the tunnel is dynamics compensation circuits 9.W6, W7, W8 establish for adapting to dissimilar transmitters among the figure.W6 changes DC potential, and W7 changes output amplitude, and W8 changes compensation magnitude.U5 after amplifying with compensating signal in adder 11 additions after amplifier 12 amplifies output.U0 is sent to the comparator of pulse width modulator.

Embodiment 2, and Fig. 6 is the structured flowchart of second kind of implementation of the present utility model, the part that it is identical with label among Fig. 5, and the form of its formation and each concrete member and embodiment's 1 is basic identical.Having only audio frequency amplifier 1 is that former machine audio frequency resistance-capacitance coupled amplifier is changed into the direct-current coupling amplifier, its concrete structure (see figure 8) is by the operational amplifier IC10 amplifier element of deciding, audio signal is connected to the inverting input of IC10 through resistance R 39, the DC level that obtains from potentiometer W9 is connected to the in-phase input end of IC10 through resistance R 40, and resistance R 41 cross-over connections are between the inverting input and output of IC10.Because changing AC coupled is direct-current coupling, and applied an anti-phase DC level to offset the flip-flop in the feedback signal, thereby eliminated the influence of negative feedback to the transient state controlled characteristic, therefore corresponding dynamics compensation circuits 9 and the adder of saving among Fig. 5 11 is simplified to the version of Fig. 6.In physical circuit shown in Figure 7, as long as K switch 2 is pulled position b from position a, make the input end grounding of dynamics compensation circuits, then the resistance R 35 in dynamics compensation circuits and the adder is ineffective, promptly become the physical circuit schematic diagram of second kind of structure of block diagram, its operation principle is basic identical with embodiment 1 also.

Last two kinds of implementations, have all obtained and corresponding to, the satisfactory controlled characteristic curve of steady-state characteristic when carrying out transient test owing to all solved degenerative influence.This explanation has only and has solved degenerative influence, and the dynamic peak level that carrier wave just can be followed modulation signal changes.All be connected to low pass filter among the branch road B in two implementations in addition, eliminated the additional interference of saddle-shape characteristic.

Claims

1, a kind of year filter amplitude modulation apparatus that floats that inserts in the series feed pulse-width modulated transmitter, audio signal is imported former machine audio frequency amplifier 1 by input, at audio signal input end and connect one tunnel passage that produces the carrier wave controlled signal, this passage is serially connected with all-wave peak rectifier 2, time constant treatment circuit 3, export control signals in channel rear portion by amplifier 12, it is characterized in that in time constant treatment circuit 3 back and connect two branch roads, be serially connected with summing amplifier 4 and amplitude limiter 5 among the branch road A, be serially connected with low pass filter 6 and summing amplifier 7 among the branch road B, the output of two branch roads connects comparison follower 8, relatively the output one tunnel of follower 8 connects the first input end that is connected to adder 11 after the dynamics compensation circuits 9, the output of another road connects second input that is connected to adder 11 behind the amplifier 10, and the output of adder 11 is connected to the input of amplifier 12.

2, amplitude modulation apparatus with floating carrier according to claim 1, it is characterized in that summing amplifier 4 connects into amplifying circuit by operational amplifier IC4, resistance R 11-R16, potentiometer W3, input signal is connected to the inverting input of IC4 through resistance R 9, and the DC level that is obtained by potentiometer W2 is connected to the in-phase input end of IC4 through resistance R 10.

3, amplitude modulation apparatus with floating carrier according to claim 1 is characterized in that amplitude limiter 5 is voltage stabilizing didoe D5, is connected between the output and ground wire of summing amplifier 4.

4, amplitude modulation apparatus with floating carrier according to claim 1 is characterized in that lowpass wave device 6 is connected and composed by operational amplifier IC5, resistance R 17-R19, capacitor C 2-C4, and input signal is connected to the in-phase input end of IC5.

5, amplitude modulation apparatus with floating carrier according to claim 1 is characterized in that comparison follower 8 is connected and composed by diode D6, D7 and resistance R 20.

6, amplitude modulation apparatus with floating carrier according to claim 1 is characterized in that dynamics compensation circuits 9 by operational amplifier IC8, resistance R 32, R33, and capacitor C 5 and potentiometer W8 connect and compose, and input signal is connected to the in-phase input end of IC8.

7, amplitude modulation apparatus with floating carrier according to claim 1 is characterized in that adder 11 by resistance R 34, R35 and connect and constitute, and the output of dynamics compensation circuits 9 meets R35 through potentiometer W8, and the output of amplifier 10 meets R34 through potentiometer W17.

8, a kind of amplitude modulation apparatus with floating carrier that inserts in the series feed pulse-width modulated transmitter, audio signal is by input input audio frequency amplifier 1, at audio signal input end and connect one tunnel passage that produces the carrier wave controlled signal, this passage is serially connected with all-wave peak rectifier 2, time constant treatment circuit 3,, it is characterized in that by amplifier 12 output control signals in channel rear portion:

A, audio frequency amplifier 1 are the direct-current coupling amplifier,

B, in time constant treatment circuit 3 back and connect two branch roads, branch road A is serially connected with summing amplifier 4 and amplitude limiter 5, be serially connected with the output of low pass filter 6 and summing amplifier 7, two branch roads among the branch road B and connect comparison follower 8, relatively the output of follower 8 is connected to the input of amplifier 12.

9, amplitude modulation apparatus with floating carrier according to claim 8, it is characterized in that direct-current coupling audio frequency amplifier 1 is by the operational amplifier IC10 amplifier element of deciding, audio signal is connected to the inverting input of IC10 through resistance R 39, the DC level that obtains from potentiometer W9 is connected to the in-phase input end of IC10 through resistance R 40, and resistance R 41 is connected across between the inverting input and output of IC10.