Frequency-modulated transmitter
Technical field
The present invention relates to frequency-modulated transmitter chip design art field in digital communication.
Background technology
The directly technical scheme of modulation high frequency is adopted in the frequency modulation(FM) of traditional frequency-modulated transmitter; It is very complicated that this makes that its voltage controlled oscillator (VCO) and synthesizer phase-locked loop (PLL) design; And can't be integrated in the chip; This makes chip area increase, and does not meet the technological development direction of current chip design miniaturization.
Summary of the invention
The objective of the invention is to propose a kind of FM reflector, frequency modulation(FM) partly has been placed on the digital baseband, to simplify the design of voltage controlled oscillator (VCO) and synthesizer phase-locked loop (PLL).
A kind of FM reflector comprises audio signal input end and radiofrequency signal output, comprising:
The signal input processor is used to receive the audio signal from the audio signal input end input, and said audio signal is carried out filtering and analog-to-digital conversion;
Digital signal processing unit is used for the signal of said signal input processor output is carried out audio coding and frequency modulation(FM);
The signal output processor is used for the signal of said digital signal processing unit output is carried out filtering and digital-to-analogue conversion;
The FM signal processing is used for the signal of said signal output processor output is carried out up-conversion and power amplification, and launches;
Frequency synthesizing module is used to provide the stabilized carrier signal.
Wherein, said FM signal processing comprises:
One or more frequency mixers are used for the signal of filter output is carried out up-conversion;
The IQ modulator is used to suppress the image signal that frequency mixer is exported;
Power amplifier is used for IQ modulator output signal is carried out power amplification and launches.
Wherein, said frequency synthesizing module comprises:
Crystal oscillator is used to the reference source that provides stable;
Phase-locked loop is used to receive said crystal oscillator output signal, for said analog to digital converter, digital signal processing unit and digital to analog converter provide clock;
Frequency synthesizer is used to receive the feedback signal of said crystal oscillator and voltage controlled oscillator output, and locks voltage controlled oscillator;
Voltage controlled oscillator is used for the output of receive frequency synthesizer, and for said frequency synthesizer feedback signal is provided;
Remove 2 circuit, be used to receive said voltage controlled oscillator output signal, produce the local oscillation signal of quadrature phase for said frequency mixer.
Wherein, said digital signal processing unit comprises:
A digital acoustic coding part and a numerical frequency modulating part, said digital audio coded portion specifically comprises:
One or more desampling fir filters are used to receive corresponding said analog to digital converter output signal, and reduce the quantizing noise after sample frequency and the filtering process analog-to-digital conversion;
One or more preemphasis filters are used to receive corresponding said desampling fir filter output signal, and HFS is strengthened;
One or more audio coders are used for respectively the signal of the preemphasis of preemphasis filter output is carried out audio coding;
One or more frequency mixers are used for audio signal is carried out signal mixing, and finally produce composite signal to said digital frequency modulation part.
Wherein, said digital frequency modulation partly comprises:
Amplitude is used to change amplitude to a phase place step value of said composite signal to the transducer of phase place;
A phase accumulator is used to receive said phase place step value, and receives the control of the clock signal of said oscillator generation; This said phase accumulator comprises an adder, and under the triggering of clock signal, this adder is constant A and the addition of phase place step value, with this output phase data-signal,
A decoder read-only memory that is used for the sine amplitude data lookup table,
The phase deviation device of one 90 degree,
Phase place is used for the receiving phase data-signal to the transducer of amplitude, will convert thereof into range signal; The position of the high-order portion of said phase data signal produces the sinusoidal wave range signal I and the range signal Q of cosine wave as the address of decoder read-only memory with decoding, and wherein the range signal of cosine wave produces through the phase shifter of said 90 degree.
Wherein, The quantity of said audio signal input end is two, is respectively applied for the input of L channel, R channel, and said digital signal processing unit sound intermediate frequency encoder is two; Be used for respectively to the audio coding that carries out L+R and L-R through preemphasis L channel, right-channel signals
Wherein, said frequency mixer comprises first, second frequency mixer, and said first frequency mixer is with the signal mixing of L-R signal and 38KHz, to produce the double-side band carrier suppressed signal of an amplitude modulation(PAM); Said second frequency mixer is used for the sound signal of said L+R signal, main double-side band carrier suppressed signal and 19Khz is made up, and produces said composite signal.
The FM reflector that the present invention proposes; Through partly being placed on frequency modulation(FM) on the digital baseband; Rather than, not only simplified the designing requirement of voltage controlled oscillator (VCO) and synthesizer phase-locked loop (PLL) like this, and make it to be integrated into the chip the inside as direct modulation high frequency in the past.In addition, owing to adopted digital three-dimensional sound encoder and digital frequency modulation, make the anti-interference and tonequality of chip have increased significantly.
Further specify the present invention below in conjunction with accompanying drawing and embodiment.
Description of drawings
Fig. 1 is a FM reflector embodiment The general frame of the present invention;
Fig. 2 is Digital Signal Processing block diagram among the FM reflector embodiment of the present invention;
Fig. 3 is FM reflector embodiment medium frequency modulation block diagram of the present invention.
Embodiment
The FM reflector 100 that provides in the present embodiment, it is a novel IC chip, it is integrated analog-to-digital conversion, Digital Signal Processing and inphase quadrature (IQ) reflector etc.Analog-to-digital conversion is responsible for the audio analog signals of accepting to import and is converted digital signal to, in Digital Signal Processing, carries out signal encoding and frequency modulation(FM) then, with reflector the signal that modulates is upconverted to the broadcast receiver wave band of 100MHz then and launches.It can use the frequency synthesizer of structure on the full sheet to produce the carrier signal about 100MHz.This bright this embodiment that do not limit, the audio signal of for example importing can be signals such as stereo, monophony and multichannel.
Specifically as shown in Figure 1:
A kind of FM reflector 100 comprises audio signal input end (L channel 10, R channel 20) and radiofrequency signal output 50.Audio signal is from audio signal input end entering signal input processor 200; By filtering and analog-to-digital conversion; Get into digital signal processing unit (DSP) 300 then, by audio coding and frequency modulation(FM), entering signal output processor 400 and quilt are by filtering and digital-to-analogue conversion again; Carry out up-conversion and power amplification by 500 pairs of analog signals of FM signal processing at last and launch, wherein frequency synthesizing module 600 is responsible for providing the stabilized carrier signal.Above-mentioned module specifically comprises with the lower part:
Low pass filter (LPF) 210,220 is used for input audio signal is carried out filtering;
Analog to digital converter (ADC) 230,240 is used for the signal of low pass filter 210,220 outputs is carried out analog-to-digital conversion;
Digital signal processing unit 300 is used for the digital signal of analog to digital converter (ADC) 230,240 outputs is carried out audio coding and frequency modulation(FM);
Digital to analog converter 410,420 is used for the signal of digital signal processing unit 300 outputs is carried out digital-to-analogue conversion;
Filter 430,440, the analog signal that is used for 410,420 outputs of logarithmic mode transducer is carried out filtering;
Frequency mixer 510,520, the signal that is used for filter 430,440 outputs carries out up-conversion;
IQ two-way modulator 530 is used to suppress the image signal that frequency mixer 510,520 is exported;
Power amplifier 540 is used for IQ two-way modulator 530 output signals are carried out power amplification and launch.
Further, said frequency synthesizing module 600 comprises:
Crystal oscillator (SOC) 610 is used to the reference source that provides stable,
Phase-locked loop 620, receiving crystal oscillator 610 output signals are for analog to digital converter 230,240, digital signal processing unit 300 and digital to analog converter 410,420 provide clock;
Frequency synthesizer 630, receiving crystal oscillator 610 output signal and voltage controlled oscillator 640 feedback signals are used to lock voltage controlled oscillator 640;
Voltage controlled oscillator 640; Be used for 630 outputs of receive frequency synthesizer, and feedback signal be provided for frequency synthesizer 630;
Remove 2 circuit 650, receive voltage controlled oscillator 640 output signals, produce the local oscillation signal of quadrature phase for frequency mixer 510,520.
Further, as shown in Figure 2, said digital signal processing unit 300 comprises a digital acoustic coding part 370 and a numerical frequency modulating part 350.Digital audio encoding part 370 as input, is carried out corresponding operation to input signal 30 and 40 with a numeral left side (L), right (R) stereo channel 30 and 40 simultaneously.In the middle of this example, digital audio coded portion 370 specifically comprises:
Desampling fir filter 310 and 312 is used to receive analog to digital converter 230,240 output signals, and reduces the quantizing noise after sample frequency and the filtering process analog-to-digital conversion;
Preemphasis filter 320 and 322 is used to receive desampling fir filter 310 and 312 output signals, and HFS is strengthened, and makes the signal can be modulated more accurately.
Audio coder 330,340 is used for respectively the signal 371,372 through preemphasis is carried out the audio coding of L+R and L-R,
Frequency mixer 340 is with signal 360 mixing of L-R signal and 38KHZ, to produce the double-side band carrier suppressed signal 344 of an amplitude modulation(PAM).Wherein, the signal of 38KHZ can produce through frequency division from crystal oscillator 610;
Frequency mixer 342 makes up audio frequency (Tone) signal 362 (also can obtain through 610 frequency divisions of the oscillator on the chip) of L+R signal, double-side band carrier suppressed signal 344 and 19Khz, produces composite signal 380.
Further; In the present embodiment; The structure of the frequency modulation(FM) part 350 in the digital signal processing unit 300 is as shown in Figure 3, and digital frequency modulation part 350 uses composite signal 380 as input, and produces warbled digital output signal I and Q through direct digital frequency synthesis technology.Digital frequency modulation part 350 comprises:
Amplitude is to the transducer 351 of phase place, the amplitude to of conversion composite signal 380 phase place stepping (STEP) value;
The accumulator 352 of a phase place receives the control of said phase place step value and clock signal 60 (this clock signal also self-oscillation device 610 produces); This phase accumulator 352 comprises an adder 353, and under the triggering of clock signal 60, this adder 353 is with constant ' A ' and the addition of phase place STEP value.That is to say; As time goes on; Adder 353 adds up step value or is integrated into feedback signal ' among the A '; With this output phase data-signal 355, when the upper limit that the value 355 of the accumulation of phase data is overflowed the counting that has exceeded adder 353 in other words, adder 353 is lost the cumulative process that carry digit (BIT) repeats phase data then.Therefore, the cycle output that is similar to the sawtooth waveforms shape that phase data signal 355 is and sinusoidal (SINE) ripple is corresponding.The amplitude of composite signal 380 has determined the step value of phase accumulator 352; So just can change the cycle and the frequency of accumulator 352 output signals; The increase that is to say the phase place step value can make the output signal frequency of accumulator 352 increase with this so that the frequency that accumulator 352 overflows increases.And the minimizing of phase place step value can cause low output signal frequency, therefore will produce a frequency modulated signal.If corresponding to 2, the scope of phase place step value Δ φ is 0~2 π with the capacity of the maximum of accumulator 352, the working clock frequency of accumulator is f simultaneously
_ accu, the output signal frequency f of accumulator then
_ outBe:
The frequency of supposing accumulator output signal I or Q belongs to scope (f
1, f
2), the phase place step value just should belong to scope (2 π f
1/ f
_ accu, 2 π f
2/ f
_ accu).
Phase place is to the transducer of amplitude 354, phase deviation devices 356 that are used for 358 and one 90 degree of decoder read-only memory (ROM) of sine amplitude data lookup table, and wherein phase place converts the phase data signal of exporting 355 to range signal as input to the transducer 354 of amplitude.In realization; The position of the high-order portion of phase data signal 355 (BITS) produces the sinusoidal wave range signal I and the range signal Q of cosine wave as the address of decoder ROM358 with decoding, and wherein the range signal of cosine wave can produce through the phase shifter 356 of said 90 degree.
The warbled digital inphase signal I and the digital integration phase signal Q that come out from digital signal processing unit 300 are outputed to the signal output processor 400, and digital there I and Q signal are converted into analog signal and deliver to FM signal processing 500 then and launch.