CN1066870C - Direct conversion receiver - Google Patents

Abstract

The present invention relates to a receiver. The present invention comprises an input device which comprises an antenna and a blockage filter, wherein the output of the blockage filter is connected with an amplifier; input signals are separated, the frequency of the input signals is respectively mixed with the frequency of same-phase signals and quadrature phase signals are mixed, wherein the same-phase signals and the quadrature phase signals are generated by an oscillator in mixer circuits, and the output of each mixer circuit is added to the input ends of a low-pass filter and an amplitude-limiting circuit; the output of each low-pass filter is added to the input ends of adder circuits, wherein the first adder is used for adding the same-phase signals and the quadrature phase signals, and the second adder is used for performing subtraction to the same-phase signals and the quadrature phase signals so as to generate respective output signals which are respectively provided with a shaft arranged between the same-phase signal shaft and the quadrature phase signal shaft. The output signals, the same-phase signals and the quadrature phase signals respectively pass through the amplitude-limiting circuit and then enter a decoder circuit so as to restore signals; the output of the amplitude-limiting circuit provides signals which are quantified into eight possible phase states which are at intervals of an angle of 45 DEG. When the input signals are in GFSK modulation, a vector crosses at least one shaft; therefore, the rotary direction can be determined before data is restored. In another embodiment, a rate combiner can be used to substitute for the adder circuit, which is especially useful in pai/4-DQPSK modulation; in the pai/4-DQPSK modulation, the phase offset of each symbol is (+/-) 45 DEG or (+/-) 135 DEG and depends on bit pair combination; in the embodiment, at least eight shafts can be generated to provide 16 sections and a phase resolution of 22.5 DEG.

Description

Direct Conversion Receiver

The present invention relates to Direct Conversion (direct conversion) receiver that a kind of radio system is used.

As everyone knows, use Direct Conversion Receiver can avoid those bulky and expensive intermediate frequency (IF) band pass filters.And the use of radio frequency (RF) filter is simplified significantly, and whole receiver can be integrated on the chip piece.

In fact, one of major obstacle that successfully realizes Direct Conversion is that automatic gain control (AGC) is used in requirement, especially in digital communication environment.In Direct Conversion Receiver, AGC must realize by base band, because Modern Digital System uses burst usually, uses AGC just to seem too slow with burst like this.

With reference to figure 1 and Fig. 2, Figure 1 shows that a kind of device that often uses in the low data rate paging receiver, also comprise the antenna 2 of an input that is connected block filter (blocking filter) 4, the output of this filter is as an input of amplifier 6.The output of amplifier is added to an input of frequency mixer 8 and 10, the output of second input reception oscillator 12 of these two frequency mixers respectively.0 ° of phase angle signal that frequency mixer 8 receives from oscillator 12, and the signal that frequency mixer 10 receives from 90 ° of phase angles of oscillator 12.Frequency mixer 8 and 10 output are added in respectively on the input of low pass filter 14 and 16, and the output of low pass filter then is added to amplitude limiter 18 and 20 respectively.The output of amplitude limiter 18 is same-phase signal I, and the output of amplitude limiter 20 is 90 ° of quadrature phase signal Q.Such circuit is not need AGC's.

If the input of receiver is frequency shift keying (FSK) signal, just as coming out with vector representation among Fig. 2.Shown in left figure among Fig. 2, this input can have any phase angle, and output signal I and Q quantize to any four possible phase places later through hard-limiting (hard limiting), shown in right figure among Fig. 2.

For demodulation frequency shift keying (FSK) modulation, be necessary to set up the direction that vector rotates.In paging system, modulation index is higher, and rotation direction is forwards, because all will rotate several weeks to each data bit vector.Output signal I that is limited and Q have become the square-wave signal that differs 90 ° each other, promptly may also may lag behind in advance, and this will see the direction of rotation.By relatively limitation signal I and Q in a phase sensitive detector (such as a D type bistable multivibrator), the polarity that differs and thereby, modulation can be resumed.

But,,, may only rotate 50 ° for each data bit vector such as Gaussian Frequency Shift Keying (GFSK) more composing under the effective low modulation index situation.This just means that vector can remain in the quadrant fully, so the output of amplitude limiter does not change.Data are expendable in this case.

One object of the present invention just provides a kind of Direct Conversion Receiver of using with phase modulated signal, and need not to use AGC.

According to the present invention, this receiver comprises the device that is used for receiving by the input signal of radio frequency media transmission, be used for producing the device of same-phase and quadrature phase signal and being used to produce with the same-phase of burst hard-limiting signal form and the device of quadrature phase signal from the signal that receives, it is characterized in that this receiver comprises the circuit arrangement that is used for producing the additional shaft between same-phase and quadrature phase signal axle, can produce burst hard-limiting signal by this additional shaft, also comprise decoding device in addition, be used for receiving described burst hard-limiting signal and the data that produce corresponding to the radiofrequency signal that receives.

This circuit arrangement can comprise first and second adder circuits, wherein first adder is used for a same-phase signal and quadrature phase signal addition, and second adder is used for a same-phase signal and quadrature phase signal and subtracts each other, thereby produces the signal with axle between same-phase signal axle and quadrature phase signal axle.

This circuit arrangement can comprise a ratio combiner, is used for producing 8 axles between same-phase signal axle and quadrature phase signal axle.

With reference now to description of drawings various embodiment of the present invention.

Figure 3 shows that the Direct Conversion Receiver of four amplitude limiters of a kind of use.

Figure 4 shows that the vector signal explanation of four receivers.

Figure 5 shows that the block diagram of FSK decoder.

Figure 6 shows that the block diagram of the Direct Conversion Receiver of a kind of n of use amplitude limiter.

Figure 7 shows that the block diagram of PI/4-DQPSK (difference quadrature phase shift keying) decoder.

With reference to figure 3, this figure is depicted as the block diagram of the Direct Conversion Receiver of four amplitude limiters of a kind of use.Receiver has as shown in the figure overcome shortcoming of the prior art by the additional shaft of introducing effectively between the axle of same-phase signal I and quadrature phase Q.Its simplest embodiment be exactly by take out earlier between same-phase signal I and the quadrature phase signal Q and with poor, then these two new signals of called after A and B are carried out hard-limiting, thereby have added 45 ° and 135 ° of two additional shafts, as shown in the figure.This receiver comprises an antenna 22 that is connected to block filter 24, and the output of block filter is added to amplifier 26.The output of amplifier then adds to the first input end of mixer 28 and 30 respectively.The same-phase signal I that mixer 28 receives from oscillator 32, the quadrature phase signal Q that circuit 30 receives from oscillator 32.Mixer 28 and 30 output then are added to the input of low pass filter 34 and 36 respectively.The output of filter 34 provides same-phase signal, is added to the input of amplitude limiter 42, the input of adder circuit 38 and the input of adder circuit 40.Similarly, the output of filter 36 provides quadrature phase signal, is added to the input of amplitude limiter 48, another input of adder circuit 40 and another input of adder circuit 38.Adder 38 produces output signal A, represent two input signals and, and adder 40 generation output signal B represent the poor of two input signals.The output of adder 38 is added to amplitude limiter 44, and the output of adder 40 is added to the input of amplitude limiter 46.Adder 42-48 produces an output signal respectively and is added to decoder 50, and decoder 50 produces an outputting data signals on output signal line 52.

About the polar plot of Fig. 3 as shown in Figure 4.Four axles have produced 8 intervals, provided effectively by the signal of hard-limiting and to be quantified as 8 signals of phase state of 45 ° of may being separated by, when input signal was the GFSK modulation signal, vector passed an axle to I haven't seen you for ages, therefore just can set up the direction and the restore data of rotation.

With reference to figure 4, left figure demonstrates input signal can have any phase angle, and right figure demonstrates through later output of hard-limiting and is quantified as 8 possible phase states.

The decoding of data can be to realize that decode procedure as shown in Figure 5 in the digital form binary signal that amplitude limiter 42-48 is exported from Fig. 4.Demonstrate a kind of FSK decoder among Fig. 5, it comprises combinational logic circuit 54, and this circuit receives input signal I, A, B and the Q from amplitude limiter 42-48 among Fig. 4.The output of combinational logic circuit is connected to the input of delay circuit 56 and the input of adder circuit 58.The output of delay circuit 56 is connected on another input of adder circuit 58.The output of adder circuit 58 then is connected on the input of average circuit 60, and the output of average circuit 60 is added to hard limiter 62, and hard limiter 62 is to output line 64 dateouts.

Can use simple combinational logic circuit to produce from 0 to 7 binary region and export, between the phase region at these output representation signal moment places.By the interval value before from the current interval value, deducting (mould 8 computings), can obtain a series of pulses that can just can bear, its positive and negative direction that depends on rotation.Also form a sample frequency phase discriminator in addition effectively.For fear of aliasing, delay cell should be less than half of bit period.Pulse train by average, is limited in circuit 62 in circuit 60 then, thereby takes out data.

In every bit phase skew modulation scheme still less (such as PI/4-DQPSK or GFSK with extremely low BT factor, wherein B is the bandwidth of modulated filter, T is a bit period), can expand this technology by introducing more axle, thereby improve phase resolution.This notion as shown in Figure 6.

With reference to figure 6, another embodiment of the invention is described now, and shows the Direct Conversion Receiver of using n amplitude limiter.

This receiver comprises antenna 66, and it is to RF filter 68 FD feeds, and the output of filter 68 is connected to the input of amplifier 70.The output of amplifier is added to the input of mixer 72 and the input of mixer 74.Mixer 72 and second input of 74 receive the output signal from oscillator 76, and wherein same-phase signal is added to frequency mixer 72, and quadrature phase signal is added to frequency mixer 74.The output of mixer 72 is added to low pass filter 78, and similarly, the output of mixer 74 is added to low pass filter 80.Filter 78 and 80 output add to ratio combiner 82 respectively, and are added to the input of amplitude limiter 84 and 92 respectively.Ratio combiner 82 produces a plurality of output signals, and its each signal adds to the input of amplitude limiter 86-90 respectively.And the output of each amplitude limiter all adds to an input of decoder circuit 94, and this decoder is used for producing an output signal on output line 96.

In PI/4-DQPSK modulation, the phase deviation of each symbol is ± 45 ° or ± 135 °, this depends on the right combination of bit (00,01,10 or 11).In receiver apparatus as shown in Figure 6, requirement has 8 axles (with 8 amplitude limiters) thereby provides the interval of 0-15 and 22.5 ° phase resolution at least.Decode procedure also can be slightly different with the situation of FSK, because need three to judge that thresholding detects the polarity and the size of phase shift.Decoder as shown in Figure 7.

With reference to figure 7, decoder circuit comprises a logical circuit 98, and this logical circuit is from amplitude limiter circuit 84-98 receiving inputted signal (Fig. 6).The output of logical circuit is added to the input of adder circuit 102 and the input of delay circuit 100.The output of delay circuit 100 is added to another input of adder circuit 102.The output of adder circuit 102 is connected to the input of average circuit 104, the output of average circuit then is added to three threshold device 106,108 and 110, and these threshold device are used to output and threshold level that is added on their second inputs of comparison average circuit 104.The output of threshold device 106-110 all is added to the input of logical circuit 112, and this logical circuit produces outputs data bits on output line 114 and 116.

It will be appreciated that it is possible changing in the scope of following claim and revise for those skilled in the art, this receiver mainly is at phase place or frequency modulation schemes.Yet, can see that in the system that must keep envelope variation (such as for equilibrium) envelope of signal can obtain from received signal intensity indication (RSSI) output of amplitude limiter.Because this will be a log-compressed envelope, change so need an antilogarithm function to recover linear amplitude.

Claims (11)

1. receiver, this receiver comprises the device that is used for receiving by the input signal of radio frequency media transmission, be used for producing the device of same-phase and quadrature phase signal and being used to produce with the same-phase of burst hard-limiting signal form and the device of quadrature phase signal from the signal that receives, it is characterized in that, this receiver comprises the circuit arrangement that is used for producing the additional shaft between same-phase and quadrature phase signal axle, can produce burst hard-limiting signal by this additional shaft, also comprise decoding device in addition, be used for receiving described burst hard-limiting signal and the data that produce corresponding to the radiofrequency signal that receives.

2. according to the receiver of claim 1, wherein the circuit arrangement of additional shaft comprises first and second adder circuits, first adder is used for a same-phase signal and quadrature phase signal with any ratio addition, second adder is used for a same-phase signal and quadrature phase signal and subtracts each other with any ratio, produces the signal with axle between same-phase signal axle and quadrature phase signal axle by this.

3. according to the receiver of claim 2, wherein be added to the input of an amplitude limiter respectively from the output signal of first and second adders, this amplitude limiter produces described burst hard-limiting signal, and described same-phase and quadrature phase signal also are added to an amplitude limiter respectively, and the output signal of this amplitude limiter is added to the input of described decoding circuit respectively.

4. according to the receiver of above any claim, it is characterized in that decoding circuit comprises a combinational logic circuit, be used for receiving output signal from amplitude limiter, and when using four axles, also be used for producing from 0 to 7 interval output, between the phase region at their representation signal moment places, thereby and comprise that the vector that is used for deducting before produces a device that depends on the pulse train of vector rotation direction from current vector.

5. according to the receiver of claim 4, wherein pulse train is added to average circuit and amplitude limiter circuit, and amplitude limiter circuit is used for extracting data from described pulse train.

6. according to the receiver of above any claim, wherein decoding device is the FSK decoder.

7. according to the receiver of claim 1, wherein the circuit arrangement of additional shaft comprises a ratio combiner, and it is used for producing 8 axles between same-phase and quadrature phase signal axle.

8. according to the receiver of claim 7, the output signal of its ratio combiner, same-phase signal and quadrature phase signal are added to amplitude limiter circuit respectively, and the output signal of amplitude limiter circuit then is added to the input of decoder circuit respectively.

9. receiver according to Claim 8, wherein decoder circuit comprises the input logic device, it is used for from the amplitude limiter receiving inputted signal, and when using 8 axles, also be used for producing from 0 to 15 interval output signal, thereby and comprise that the vector that is used for deducting before produces the device of an output signal sequence from current vector.

10. according to the receiver of claim 9, wherein output signal sequence is added to an average circuit, the output of average circuit is added to the input of three decision circuitry respectively, decision circuitry is used for detecting the size and the polarity of phase shift, the output of each decision circuitry all is connected on the output logic circuit, and this logical circuit is used for producing data output signal on output data line.

11. according to the receiver of each claim in the claim 1 or 8,9, wherein decoding device is the PI/4-DQPSK decoder.

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