CN1988397A - Frequency modulation receiver and its demodulation method - Google Patents

Abstract

This invention relates to a FM receiver and its demoduoation method, in which, the FM receiver is composed of a Hartely structure mixture, an image suppression filter, a limiter and a FM demodulating circuit characterizing that said circuit includes two routes of orderly connected delay circuits, mixing circuits and addive circuits, and an integral circuit connected by a differential circuit and an division circuit, in which, the mixing circuits in the two routes are connected crossly, which realizes demodulation to FM base band signals and overcomes the hard requirement to delay circuit in the traditional FM signal demodulation circuit and the error problem of sine signal approximation.

Description

A kind of fremodyne and demodulation method thereof

Technical field

The present invention relates to a kind of fremodyne that is used for, especially refer to accurately to isolate by its demodulator circuit the fremodyne of baseband signal.

Background technology

The superhet radio frequency receiver is still the main flow scheme of radio frequency receiver at present.Although zero intermediate frequency (Zero IF) technology has been carried out extensive studies, the radio frequency receiver of zero-if architecture still just is used in the low-grade radio frequency receiver, as beeper (Paging).In order to improve the integrated level of radio frequency receiver,,, be integrated into chip internal as filter some outer devices of chip.In the superhet radio frequency receiver, the IF-FRE of high if architectures is too high, has limited the outside that intermediate-frequency filter must be placed on chip, realizes with discrete device.And in the Low Medium Frequency structure, the frequency of intermediate frequency is very low, can realize intermediate-frequency filter with integrated circuit, is integrated in the inside of chip.So becoming a kind of preferred plan of radio frequency receiver, the Low Medium Frequency receiver architecture selects.

The problem of Low Medium Frequency radio frequency receiver maximum is how to suppress mirror image (image) signal.In order to suppress image signal, frequency mixer generally adopts hartley (Hartely) structure or the frequency mixer of my (Weaver) structure only.What frequency mixer was exported is the two-way orthogonal signalling, and this signal process image-reject filter is the image signal filtering.Intermediate frequency amplifier is a kind of linear amplifier, output I (t) and Q (t) signal.I (t) and Q (t) comprise intermediate-freuqncy signal, and the task of last demodulator is separated baseband signal exactly from I (t) and Q (t) signal.

Fig. 1 is the structure of the present Low Medium Frequency radio frequency receiver that generally adopts.Comprise frequency mixer 100, image-reject filter 200, amplitude limiter 300 and the demodulator circuit 400 of Hartely structure '.Input signal is radio frequency (RF) signal that antenna receives, and radiofrequency signal is delivered to low noise amplifier (LNA) circuit through impedance matching network.LNA exports a pair of differential signal, is input to the frequency mixer 100 of Hartely structure, and the frequency of signal drops to intermediate frequency (IF).Through behind image-reject filter 200 and the amplitude limiter 300 (intermediate frequency amplifier), I of output (t) and Q (t) enter demodulator circuit 400 '.

After the process mixing of RF signal and low pass filter of input, the signal of output is (image signal is in low side):

At I ' channel:

RF Xin Hao @IF: $\frac{1}{2}\mathrm{Sin}({\mathrm{\ω}}_{\mathrm{RF}}-{\mathrm{\ω}}_{\mathrm{LO}})t=\frac{1}{2}\mathrm{Sin}\left({\mathrm{\ω}}_{\mathrm{IF}}t\right)---\left(1\right)$

Image Xin Hao @IF: $\frac{1}{2}\mathrm{Sin}({\mathrm{\ω}}_{\mathrm{image}}-{\mathrm{\ω}}_{\mathrm{LO}})t=-\frac{1}{2}\mathrm{Sin}\left({\mathrm{\ω}}_{\mathrm{IF}}t\right)---\left(2\right)$

At Q ' channel:

RF Xin Hao @IF: $\frac{1}{2}\mathrm{Cos}({\mathrm{\ω}}_{\mathrm{RF}}-{\mathrm{\ω}}_{\mathrm{LO}})t=\frac{1}{2}\mathrm{Cos}\left({\mathrm{\ω}}_{\mathrm{IF}}t\right)---\left(3\right)$

Image Xin Hao @IF: $\frac{1}{2}\mathrm{Cos}({\mathrm{\ω}}_{\mathrm{image}}-{\mathrm{\ω}}_{\mathrm{LO}})t=\frac{1}{2}\mathrm{Cos}\left({-\mathrm{\ω}}_{\mathrm{IF}}t\right)---\left(4\right)$

Suppose that baseband signal is a kind of warbled signal, be respectively through the signal behind the intermediate frequency amplifier:

I(t)＝Sin(ω _IFt+(t)) (5)

Q(t)＝Cos(ω _IFt+(t)) (6)

The task of demodulator is that  (t) Signal Separation is come out.

The baseband signal of exporting in Fig. 1 is:

The m that obtains (t) is exactly stereosonic baseband signal.

But establishment (7) will be satisfied following condition:

Condition one: τ is enough little in delay, satisfies: $\mathrm{\ι}\≤\frac{0.01}{\mathrm{\π}*f_{\max }}$ ,, generally get f for FM (frequency modulation(FM)) audio frequency _Max=20KHz;

Condition two: delay will produce 90 ° phase shift, that is: ω _cτ=90 °;

Condition three: $\mathrm{BB}\left(t\right)=\frac{1}{2}*\mathrm{Sin}[K*\mathrm{\τ}*m\left(t\right)]\≈\frac{1}{2}\mathrm{K\τm}\left(t\right)$

It is very difficult requiring group delay (group delay) to equal 90 ° in the application of reality.In order to realize 90 ° additional a series of regulating circuits of phase shift, or realize with discrete device.If " condition two " is false, then " condition three " can produce very big error.

Summary of the invention

The purpose of this invention is to provide a kind of more exact solution and access fremodyne and the demodulation method thereof that is included in baseband signal in the radiofrequency signal phase place, and overcome of the harsh requirement of common demodulator postponing.

The demodulation method of a kind of fremodyne provided by the present invention comprises: postpone step: the signal of the big device in intermediate frequency side of two-way quadrature input is straight-through through one the tunnel respectively, and No. one delay circuit postpones, and obtains four road signals; The mixing step: the inhibit signal that delay circuit obtains and self straight-through non-inhibit signal mixing, and the signal mixing straight-through with the non-delay of the other side's quadrature, export two paths of signals respectively; The addition step: corresponding with it the respectively non-inhibit signal addition of self leading directly to of inhibit signal that postpones mixing output obtains the intermediate frequency cosine signal; The inhibit signal that postpones mixing output is subtracted each other the sinusoidal signal that obtains intermediate frequency with the other side's non-inhibit signal respectively, the output two paths of signals; Differentiation step: the intermediate frequency sinusoidal signal of add circuit output is input to differential circuit; Division steps: the signal of differential circuit output is input to division circuit as dividend, and the intermediate frequency cosine signal of add circuit output is as divisor; Integration step: the signal of division circuit output is through signal that is directly proportional with baseband signal of integrating circuit output.

In the demodulation method of above-mentioned fremodyne, input signal is the intermediate-freuqncy signal of two-way quadrature, obtains four road mixed frequency signals through signal and the other side after delay back and self mixing and the delay without the signal mixing that postpones separately.

In the demodulation method of above-mentioned fremodyne, four road mixed frequency signals, the cosine signal that postpones the two paths of signals addition acquisition intermediate frequency of back and self signal mixing postpones the back and subtracts each other without the two paths of signals of the signal mixing acquisition of delay with the other side, obtains the sinusoidal signal of intermediate frequency.

In the demodulation method of above-mentioned fremodyne, the two-way intermediate-freuqncy signal, wherein the differential of sinusoidal intermediate-freuqncy signal is compared with the cosine intermediate-freuqncy signal, obtains the second differential signal of phase signal.

In the demodulation method of above-mentioned fremodyne, phase place second differential signal obtains the signal that is directly proportional with phase place one subdifferential through an integrating circuit, and this signal is the signal that is directly proportional with the baseband signal of modulating frequency.

The present invention also provides a kind of fremodyne, form by Hartely structure frequency mixer, image-reject filter, amplitude limiter and frequency modulation demodulation circuit, it is characterized in that, described frequency modulation demodulation circuit comprises delay circuit, mixting circuit and the add circuit that two-way connects successively, and be connected integrating circuit by differential circuit with division circuit respectively, wherein, the mutual interconnection of the mixting circuit in the two-way.

Adopted above-mentioned technical solution, circuit of the present invention has been realized the demodulation to frequency modulation signal baseband signal, overcome in traditional frequency modulation signal demodulating circuit structure harsh requirement to delay circuit, also overcome simultaneously the error problem of sinusoidal signal approximation, the baseband signal that demodulates is more accurate.

Description of drawings

Fig. 1 is the circuit block diagram of common Low Medium Frequency radio frequency receiver;

Fig. 2 is the circuit block diagram of fremodyne of the present invention;

Fig. 3 is the schematic diagram of Hartely frequency mixer among Fig. 2.

Embodiment

As shown in Figure 2, the present invention, promptly a kind of fremodyne is made up of frequency mixer 100, image-reject filter 200, amplitude limiter 300 and the demodulator circuit 400 of Hartely structure.

As shown in Figure 3, suppose that it is ω that LNA amplifies the signal angular frequency of exporting _RF, the angular frequency of image signal is ω _Image

In order to remove image signal, the signal that promptly aforementioned (2) and (4) formula are represented, the most frequently used method is to adopt multiphase filter (Polyphase filter) cancellation (2) and (4) formula image signal.Also can adopt complex filter, suppress image signal by frequency translation.200 circuit among the figure just.The 300th, two-way intermediate frequency amplifier, or amplitude limiter.Intermediate frequency amplifier 300 output two paths of signals I (t) and Q (t).

I (t) signal one tunnel is through delay circuit 408, and delay time T is very little.Another road I (t) does not postpone, through mixing in the frequency mixer 401, and output signal A:

Q (t) and I (t-τ) mixing in frequency mixer 402, output signal B:

Mixing in signal Q (t-τ) the process frequency mixer 403 of I (t) signal and Q (t) process delay circuit 409, output signal C:

Q (t) signal and the signal mixing in frequency mixer 404 that itself postpones through delay circuit 409, output signal D:

A, B, these signals of C, D all will be through the low pass filter in the frequency mixer 401,402,403,404 separately the frequency-doubled signal filterings in the signal, just in various first of formula (7), (8), (9), (10).

Signal C cut signal B obtains signal E:

E＝C-B＝Sin[ω _IFτ+(t)-(t-τ)]≈Sin[ω _IFτ+τ′(t)] (12)

Signal A and signal D summation obtain signal F:

F＝A+D＝Cos[ω _IFτ+(t)-(t-τ)]≈Cos[ω _IFτ+τ′(t)] (13)

(12) signal is compared with (13) through differential, is obtained:

To (14) signal H (t) integration, obtain the signal that is directly proportional with baseband signal:

BB(t)＝K _v*τ*′(t)＝K _vτ*m(t) (15)

M (t) signal be exactly by with, difference signal and the synthetic baseband signal of pilot signal, finished demodulation function.

The present invention has realized the demodulation to frequency modulation signal baseband signal, has overcome in traditional frequency modulation signal demodulating circuit structure the harsh requirement to delay circuit, has also overcome the error problem of sinusoidal signal approximation simultaneously, and the baseband signal that demodulates is more accurate.

In sum, demodulator circuit of the present invention can demodulate the demodulator circuit of baseband signal among I (t)/Q (t), but has overcome in the prior art the harsh requirement of " condition two ", does not also have the restriction of " condition three " simultaneously.

Although the present invention explains with concrete syntax architectural feature and/or method function, should be understood that the present invention that appended claims limits must be limited to illustrated concrete feature or function.On the contrary, these concrete features and function are just disclosed as the exemplary embodiment of the present invention for required protection.

Claims (6)

1. the demodulation method of a fremodyne comprises:

Postpone step: the signal of the big device in intermediate frequency side of two-way quadrature input is straight-through through one the tunnel respectively, and No. one delay circuit postpones, and obtains four road signals;

The mixing step: the inhibit signal that delay circuit obtains and self straight-through non-inhibit signal mixing, and the signal mixing straight-through with the non-delay of the other side's quadrature, export two paths of signals respectively;

The addition step: corresponding with it the respectively non-inhibit signal addition of self leading directly to of inhibit signal that postpones mixing output obtains the intermediate frequency cosine signal; The inhibit signal that postpones mixing output is subtracted each other the sinusoidal signal that obtains intermediate frequency with the other side's non-inhibit signal respectively, the output two paths of signals;

Differentiation step: the intermediate frequency sinusoidal signal of add circuit output is input to differential circuit;

Division steps: the signal of differential circuit output is input to division circuit as dividend, and the intermediate frequency cosine signal of add circuit output is as divisor;

Integration step: the signal of division circuit output is through signal that is directly proportional with baseband signal of integrating circuit output.

2. according to the demodulation method of the described fremodyne of claim 1, it is characterized in that: input signal is the intermediate-freuqncy signal of two-way quadrature, obtains four road mixed frequency signals through signal and the other side after delay back and self mixing and the delay without the signal mixing that postpones separately.

3. according to the demodulation method of the described fremodyne of claim 2, it is characterized in that: described four road mixed frequency signals, the two paths of signals addition that postpones back and self signal mixing obtains the cosine signal of intermediate frequency, postpone the back and subtract each other without the two paths of signals that the signal mixing that postpones obtains, obtain the sinusoidal signal of intermediate frequency with the other side.

4. according to the demodulation method of the described fremodyne of claim 3, it is characterized in that: described two-way intermediate-freuqncy signal, wherein the differential of sinusoidal intermediate-freuqncy signal is compared with the cosine intermediate-freuqncy signal, obtains the second differential signal of phase signal.

5. according to the demodulation method of the described fremodyne of claim 4, it is characterized in that: described phase place second differential signal, obtain the signal that is directly proportional with phase place one subdifferential through an integrating circuit, this signal is the signal that is directly proportional with the baseband signal of modulating frequency.

6. fremodyne, form by Hartely structure frequency mixer, image-reject filter, amplitude limiter and frequency modulation demodulation circuit, it is characterized in that, described frequency modulation demodulation circuit comprises delay circuit, mixting circuit and the add circuit that two-way connects successively, and be connected integrating circuit by differential circuit with division circuit respectively, wherein, the mutual interconnection of the mixting circuit in the two-way.

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