CN1163514A

CN1163514A - Improved sampling system for radio frequency receiver

Info

Publication number: CN1163514A
Application number: CN 96112449
Authority: CN
Inventors: 罗伯特·L·库伯
Original assignee: Paradyne Corp
Current assignee: Paradyne Corp
Priority date: 1995-10-17
Filing date: 1996-10-17
Publication date: 1997-10-29

Abstract

A radio frequency (rf) receiver adapted to receive a number of different digitally modulated rf input signals such as quadrature amplitude modulated QAM and vestigial side band VSB rf input signals includes circuitry for down converting the rf input signals to an intermediate frequency IF range having a centre frequency fc2 and a bandwidth of Bhz and converter circuitry for sampling the IF signals and then producing corresponding baseband signals. In a preferred embodiment, the intermediate frequency signals are applied to a sample and hold circuit which is sampled at a frequency fs and whose output is coupled via a low pass filter to an analog-to-digital converter whose output is then applied to a Hilbert filter for demodulating the sampled signals and producing baseband signals. In-phase I and quadrature Q signals are produced whose phase and amplitude are not a function of different components and their tolerance of different conduction paths.

Description

The improved sampling system that is used for radio-frequency transmitter

The present invention relates to a kind of improved radio frequency (rf) receiver system, specifically, relate to a kind of such receiver system, wherein the sampling of received signal is carried out in intermediate frequency (IF) band.

In order to understand the problem that the present invention solves better, please referring to Fig. 1, wherein show the part of TV receiver conventional in the prior art, it utilizes baseband sampling or quadrature amplitude modulation mode to operate for residual sideband (VSB).This receiver uses synchronizing indicator and simulation pilot tone to recover ring, shown in square among Fig. 1 20.For the VSB signal, only need a channel (be the I channel, comprise frequency mixer 21, filter 28 and ADC 29), thereby, only require a modulus (being ADC 29) transducer.But, need the circuit of quantum to be used to carry out synchronous detecting, this can obviously find out from piece shown in Figure 1 20.

In Fig. 1, the rf input signal 9 that receives transmits by second frequency mixer (MX2), the 3rd band pass filter (BPF17) and the IF amplifier 18 of the output of frequency mixer (MX1), second band pass filter (BPF14), the output that mixes BPF14 and second local oscillator (LO2) of the output of first band pass filter (BPF 10), amplifier (AMP11), the output that mixes AMP11 and first local oscillator (LO1), thereby produces IF signal e1 at the output of amplifier 18.In Fig. 1, the bandwidth center frequency that IF output has 6MHz is approximately 44MHz.IF signal e1 is sent to an input of frequency mixer 21, and its another input is supplied to the output of the 3rd local oscillator (LO3).The output that is defined as the frequency mixer 21 of homophase (I) signal is sent to the input of antialiasing low pass filter (AALPF) 28.Then, the output of AALPF28 is sent to N position analog to digital converter (ADC) 29.The output of ADC 29 is sent to the input of base band demodulator sheet 32.In addition, pilot tone low pass filter (pilot tone LPF) 24 has the output that output links to each other with the I of frequency mixer 21 input links to each other with input with amplitude limiter 25, and amplitude limiter 25 has the output that links to each other with the input of frequency mixer 26.

When using quadrature amplitude modulation (QAM) mode and needing decoding, another problem then appears.Because QAM has homophase (I) input and the input of quadrature (Q) base band, so needs second analog channel and second A/D converter are used for decoding input data.This is shown among Fig. 1, and wherein signal e1 is added on an input of frequency mixer 22, and its another input connects the output of LO3, is used for producing quadrature (Q) output signal.Q signal is sent to the input of antialiasing low pass filter (AALPF) 31, and its output is sent to the input of N position analog to digital converter 30.ADC 29 and 30 is used for sampled signal in baseband frequency range.The base band output QB of the base band output IB of ADC 29 and ADC 30 is sent to the input of timing recovery circuit 34 and is positioned at the input of the agc circuit 36 of demodulator 32.

Simulation pilot tone ring be included in mix in the frequency mixer 26 from the Q output of frequency mixer 22 with from the I output of amplitude limiter 25, its output is added on the input of pilot tone low pass filter (LPF) 27.The output of pilot tone LPF 27 is an analog signal, and it is added on the input of second local oscillation circuit (LO2) and it is controlled.There are some problems in the analysis showed that of prior art circuits.

At first, in the problem that exists for the complexity that produces the required synchronizing indicator element of I and Q function.

The second, because the component tolerance of frequency mixer and filter makes two analog channels (frequency mixer 21 and AALPF 28 probably; Frequency mixer 22 and AALPF 31) amplitude of the signal that transmitting is had different responses with phase place.This quality to performance has harmful effect.At title is that " Asymmetric Baseband Equalization " author is (IEEE Transactions on Communications in the article of Hikmet Sari and GeorgesKaram, Vol.36, No.9, September, 1988) way that proposed to address this problem.But, wherein proposing to use asymmetric structure, the tap that it requires reaches the twice of conventional symmetrical equilibrium device and requires two ones adaptive control.

Note instructing the sampling (being the output of AALPF28 and 31) of carrying out base band level in the prior art as shown in Figure 1.In the baseband level buffer, sample be because:

A. quadrature imperfection on the modulator carrier wave;

B. in I and Q baseband analog interchannel amplitude imbalance; And

C. at I and Q baseband analog interchannel unbalance in phase.

Thereby, the objective of the invention is to address these problems with a kind of better simply system, this system use less elements and avoid along two different channel transfers and produce I, Q signal and in signal the problem of introducing out of phase and different amplitude factors.

Use system of the present invention to comprise to be used for the tuner of the front end of controlling high definition TV (HDTV) receiver and the device of IF level, make receiver can use quadrature amplitude modulation (QAM) scheme of residual sideband (VSB) and digital modulation.

In using system of the present invention, the output of IF level is sampled, and generally is to sample in base band level in the prior art.

Use system of the present invention not need many like that in the prior art synchronizing indicator circuit.Thereby reduced the expense of circuit.In addition, perhaps be prior, VSB and QAM signal pass through along same analog channel.Thereby not the signal that enters is not introduced two different passages of different delays and different gain coefficient.

In the accompanying drawings, identical symbolic representation components identical.Wherein:

Fig. 1 is the calcspar that has high definition TV (HDTV) receiver of baseband sampling according to prior art;

Fig. 2 is the part calcspar according to the HDTV receiver of the IF of having level sampling of the present invention;

Fig. 3 is the oscillogram relevant with the circuit of Fig. 2; And

Fig. 4 is the part calcspar according to the another kind of HDTV receiver of the IF of having level sampling of the present invention.

Fig. 2 represents to use system of the present invention with the form of square.The importation of receiver is similar to the importation of prior art.That is, comprise that scope is added to band pass filter 10 from the RF input 9 of 50 to 800MHz signals, its output " A " is added to the input of amplifying stage 11, and the gain of amplifying stage 11 is by 40 controls of automatic gain control (AGC) circuit.The output of the output of amplifier 11 and the first local oscillator LO1 is added to the first frequency mixer MX1.The output of frequency mixer MX1 " B " is added on the input of 920MHz band pass filter 14.The part that has just illustrated is identical with prior art circuits shown in Figure 1.

In Fig. 2, the output of the output of band pass filter 14 " C " and the second local oscillator LO2 is added on the second frequency mixer MX2, carries out mixing there.The output of frequency mixer MX2 " D " is added on the input of band pass filter 16.In Fig. 2, the centre frequency of LO2 is 882,34MHz, and the centre frequency of band pass filter 16 designs is 37.66MHz.For the centre frequency of the 882.34MHz that selects LO2 with to select centre frequency be that the importance of the band pass filter 16 of 37.66MHz is discussed below.The output E of band pass filter 16 is added on the input of IF amplifier 18, and its gain is by one or several signal controlling from agc circuit 40.The output elm of amplifier 18 is added on the input of change-over circuit 50.Signal E and elm are in the frequency band that centre frequency is approximately 37.66MHz, shown in the waveform of being represented by IF OUT among Fig. 3.

Referring to Fig. 2, elm is added to the sampling of 43.04 million samplings of per second (MSPS) operation and the input of maintenance (S/H) circuit 51 again.Sampling and holding circuit 51 for example can be the circuit as Analog Device AD 9101, or any available other circuit.The output G of S/H 51 has the frequency spectrum of being represented by S/H OUT as Fig. 3.As shown in Figure 3, centre frequency is that the signal band IF OUT of 37.66MHz is the centre frequency of 5.38MHz by down converted, has the mirror image of centre frequency for-5.38MHz.The bandwidth of signal is around centre frequency expansion ± 2.69MHz.Notice that S/H output comprises that also centre frequency is the signal band of 37.66MHz, has the mirror image that centre frequency is 48.42MHz.S/H output also comprise have respectively centre frequency for-37.66MHz and-the signal band of 48.42MHz.Be also noted that and in Fig. 3, may have pilot tone (PT) signal of representing by vertical arrows.

The output of S/H 51 (G) is sent to antialiasing low pass filter (AALPF) 53, thereby produces the output (H) with frequency spectrum of representing with AALPF OUT among Fig. 3.Filter 53 has been eliminated has 5.38MHz centre frequency and having-all signals of the signal outside of the mirror image of the centre frequency of 5.38MHz.The output of filter 53 (H) is added to the input of N position analog-to-digital conversion (ADC) circuit 52, and analog to digital conversion circuit 52 is with conversion or the sampling rate operation of 21.52MSPS.ADC 52 for example can be 10 ADC, for example SPT 7855 or any similar available circuit of being made by SignalProcessing Technologies.The output of A/D converter 52 (P) has the frequency response shown in the waveform of representing with A/D OUT among Fig. 3.Because in A/D OUT the cycle repeat not overlapping, so the sampling processing of A/D converter does not have aliasing.

S/H 51 operates under the frequency of 43.04MHz, even signal bandwidth only is 6MHz.Because S/H 51 is necessary for the signal with the frequency content in the scope that is between the 34-40MHz and is designed.Like this, when having this high centre frequency (being 37.66MHz), just can not use the A/D converter of sampling simply with the bandwidth (12MHz) that doubles 6MHz signal band.

Like this, though S/H 51 as mentioned above, does not need the analog-to-digital conversion frequency of 43.04MHz with the sample frequency sampling of 43.04MHz.S/H51 is used for by sampling processing the IF centre frequency being transformed into 5.38MHz from 37.66MHz.As shown in the S/H OUT waveform of Fig. 3, the bandwidth of the S/H output signal (G) of conversion will upwards expand to 8.07MHz and expand to 2.69MHz downwards.Like this, the A/D sample frequency of 21.52MHz (by the signal controlling from circuit 321 that provides on online 80) will satisfy the nyquist criterion.

In the circuit of Fig. 2, use two sample frequencys.S/H51 uses a sample frequency (43.04MHz), and A/D converter 52 uses another sample frequency (21.52MHz).Therefore, antialiasing low pass filter (AALPF) 53 is inserted between the input of the output of S/H51 and ADC52.This guarantees the energy of the sampling processing of A/D converter without undergoing 10.76MHz, thereby satisfies the nyquist criterion of ADC 52.Like this, in Fig. 2, provide the sampling clock of 43.04MHz to S/H51, and the sampling clock of 21.52MHz is provided by line 80 to ADC 52 by line 90.On the contrary, in the base band scheme of Fig. 1, need two (2) ADC transducers (29 and 30), provide 10.76MHz low sampling clock like that to ADC 29 and 30 by line 85.

The comparative descriptions of Fig. 1 and Fig. 2, the same frequency detector 20 of Fig. 1 have been sampled effectively with holding circuit 51 and have replaced, and the system of Fig. 2 only requires a N position A/D converter for VSB or QAM.

The problem relevant with the prior art of Fig. 1 has been eliminated, and do not need asymmetric equalizer.

Therefore, in using system of the present invention, the complexity of circuit has been reduced, has improved performance simultaneously.But, the system that should be noted that Fig. 2 needs and the different demodulator 320 of demodulator 32 of Fig. 1.The front end of the front end of the demodulator by comparison diagram 1 and the demodulator of Fig. 2 is its difference as can be seen.The demodulator 320 of Fig. 2 comprises that Hilbert filter 328, timing recovery circuit 321, agc circuit 322, demodulator 323, LO2 adjust circuit 325, adder 326 and fixing carrier wave demodulation table 324.Need the Hilbert filter, so that accurately be produced as quadrature-related signal I and Q that the QAM mode produces.

Be sent to the input of Hilbert filter 328 from the N position output P of ADC 52.The Hibert filter is known in the art, and comes into question, for example " Digital SignalProcessing ", A.Oppenheim and R.Schafer, Ch.7, Prentice Hall, 1975; And " Theory and Application of Digital Signal Processing ", L.Rabinerand B.Gold, pp.71-72, Prentice Hall, 1975.

Hilbert filter 328 can be by the generation of designing program of standard.The output of ADC 52 (P) be added to and have two outputs (wherein the real component of filter output represent in h1 output for h1, the input of Hilbert filter 328 h2), the quadrature component that on behalf of filter, h2 output export, h2 exports and is used for QAM.For the VSB mode, h2 can be set as zero, so as to removing any imaginary part channel.The frequency that the h1 of Hilbert filter and h2 output can be used to regulate the second local oscillator LO2.As shown in Figure 2, h1 and h2 are added on the input that LO2 adjusts circuit 325, adjust circuit 325 the output z that provides to LO2 by line 70 is provided.The predetermined quantification that makes with for example 60KHz that applies of output z signal goes on foot the frequency shift (FS) of removing in selected channel.

The effect of Hilbert filter is as follows in general: obtain an output (for example h1) by means of carry out filtering by the linear phase symmetrical impulse response, and obtain another output (for example h2) by means of carry out filtering by the impulse response of linear phase antisymmetry.In native system, the Hilbert filter is intended to be used for the QAM modulation, thereby the signal that receives is divided into real part and imaginary part as the digital filter of real number input plural number output.For the VSB mode, the Hilbert filter only passes through the real component of the signal of reception, because modulation is an one dimension.Be programmed for VSB mode receiver, make and ignore h2 imaginary part component.This realizes according to the configuration data that remains on the description VSB system in the master microprocessor 400.Though do not describe in detail, should be appreciated that to respond the QAM control signal 403 that is added on the VSB control signal 401 of master microprocessor 400 or is added on microprocessor 400 the correct operation of the described function of microprocessor 400 controls.

LO2 adjusts circuit 325 also provides signal r1 to add circuit 326.Signal r1 representative has been adjusted within the transmitter frequency of 60HHz of regulation at LO2 after, for removing the required correction of residual frequency shift (FS).The representative of signal on the online r1 is added to the supplementary angle on the fixed carrier angle, so that fully to the output of base band demodulating Hilbert filter.The fixed carrier angle is produced by fixed carrier demodulator watch circuit 324, and circuit 324 produces the output signal r2 that is added on adder (summer) network 326.Adder network 326 is used for making r1 and r2 signal plus, and produces output signal S1 and S2, and they are sine and the cosine that is used for the accumulated angle of demodulation, and described demodulation realizes with sample frequency.

Signal r1 can produce by phase-locked loop (PLL) circuit that is positioned within the LO2 adjustment circuit 325.In general, this circuit can not be handled many like that skews (approximately 1MHz) of predicting in LO2.Therefore, before this ring of operation, the major part of skew is removed by signal second.Signal r2 produces by look-up method, and details are as follows.

From two output S1 of adder 326, S2 is sent to demodulator 323, and the input of other of demodulator 323 is from the h1 of Hilbert filter 328 and h2.For the VSB mode, only use output h1, and h2 is made as zero.Demodulator 323 produces baseband signal I and Q at its output, and they are linked timing recovery circuit 321 and agc circuit 322 by

line

62 and 61 respectively.

I that produces respectively on online 62 and 61 and Q signal are the I that the output in ADC 29 and 30 produces in the prior art systems of Fig. 1, the digital equivalent signal of Q signal.

The I, the Q signal that produce according to the present invention have following advantage:

1. realize for each that I, Q accurately have the phase difference of 90 degree on all frequencies.And be the phase difference of approximate 90 degree in the prior art, and the phase difference difference between a plurality of receivers of same design.This be because, according to the present invention, I, Q signal obtain by digital Hilbert filter, and obtain by analogue means in the prior art.

2. compare with Fig. 1, I, Q signal have accurately controlled amplitude characteristic, and that the component franchise among Fig. 1 can cause that amplitude between a plurality of realizations changes is inconsistent.

Timing recovery circuit 321 is handled I, the Q signal that receives as input, because the signal that sends for QAM is to use the I of transmission, Q signal to produce.After handling, timing recovery circuit 321 clockings, this clock signal is locked to the transmitter clock signal.

Timing recovery circuit 321 produces the sampled signal of 43.04MHz, supplies with S/H51 by line 90, and produces the sampled signal of 21.52MHz, provides to ADC52 by line 80.43.04MHz clock can utilize at the voltage-controlled crystal oscillator of the inner control input signals that produce of piece 321 and produce by 43.04MHz.21.52MHz clock signal can produce by simple circuit divided by 2, to the clock signal of this circuit input 43.04MHz.

AGC 322 produces the output signal " U " that is connected to AGC control circuit 40 by line 75.Signal U is a digital signal, and the simulation control of this and prior art is different.Digital signal U can be utilized by the Bits Serial of this signal of expression is delivered to for example a plurality of D/A converters (MDAC) by agc circuit 40, and MDAC is a kind of standard component for numerically controlled AGC.

In the system of Fig. 2, for baseband system, timing recovery circuit 321 and agc circuit 322 are positioned at after the digital appropriate accent device 323, baseband system comprises fixed carrier demodulator lookup table circuit 324, (for VSB is n (2 π/8), for QAM is n (2 π/4)), and the LO2 that is used to proofread and correct any frequency shift (FS) of LO2 adjusts circuit 325.For the VSB system, LO2 adjustment scheme is digital pilot tone tracking loop.The QAM system also needs to adjust LO2, still can not comprise pilot tone for this purpose.The QAM scheme can be digital fully.Adjust the total angle of any skew sum that circuit produces in adder 326 additions as fixed carrier with by LO2.Adjust the design of circuit for the LO2 of VSB and can take and the similar form of analog loop shown in Figure 1, comprising piece 24,25,26 and 27, also can comprise other variation.The QAM ring can be derived without the help of pilot tone.

At first consider the operation of VSB system, the tracking of the pilot tone shown in Fig. 3 vertical arrows is realized by the LO2 adjustment circuit 325 interior digit phase tracking loops that use is located in the demodulator blocka 320 digitally.LO2 adjusts circuit 325 output coarse regulation control signals (second), supplies with LO2 by line 70.Be that digit phase pilot tone tracking loop attempts to remove the frequency shift (FS) on the pilot tone in a certain frequency range (for example 60KHz).If skew is greater than 60KHz, then tracking loop makes LO2 change with per step 60KHz by control line 70, is within the 60KHz up to skew.Coarse adjustment and fine tuning (fine tuning is undertaken by signal r1 that offers demodulator 323 and r2) can be stored on the channel variation circuit (RAM) in the memory circuit, and it is positioned on the demodulator blocka of the master microprocessor 400 that uses subsequently.It is impossible that these characteristics are utilized the analog phase-locked look of prior art.

The situation that this system is used for two different carriers of digital demodulation is discussed below.A carrier wave is used for the VSB system, and another carrier wave is used for the QAM system.Need selection to allow to use intermediate frequency (IF) frequency of very simple numerical demodulation for two kinds of schemes.Because in this application, QAM and SVB baud rate be by coefficient 2 related (being respectively 5.38MHz and 10.76MHz), for VSB and QAM, and need be with the sampling rate sampling A/D converter 52 of 21.52MHz.In order to satisfy the nyquist criterion, before sampling, insert the antialiasing low pass filter (AALPF) 53 of 10.76MHz.This means that sampling and holding circuit 51 must move frequency spectrum from 37.66MHz, shown in the waveform S/H OUT of Fig. 3.

For IF band pass filter 16, centre frequency is selected as 37.66MHz, thereby can realize digital demodulation by very simple angle by fixing carrier frequency.Thisly utilize the demodulation of carrier wave to have e ^(-jwcnTs)Form, wherein WC equals 2 π fc, fc is a carrier frequency, n is an integer, Ts equals 1/fs, fs is a sample frequency, at this frequency down-sampling ADC 52.

Notice that being used for to the demodulation angle that the sampled data of baseband signal is changed at last is e ^(-jwcnTs)Function, it equals CoswcnTs-jsinWcnTs, Wc=2 π fc wherein, Ts=1/fs.By selecting fc to equal kfc, wherein K is a rational, and the expression formula tube of demodulation angle turns to e ^{(j2 π n/k)}

For VSB, fc is 2.69MHz, and for QAM, fc is 5.38MHz.For two kinds of systems, fs is 21.52MHz.Therefore, equaling 4 for the value of QAM K, then equal 8 for VSB, is the function of n (2 π/4) thereby make the demodulation angle of QAM, is the function of n (2 π/8) for the demodulation angle of VSB.As an illustrative example, for QAM and VSB, the value of demodulation angle can be calculated as follows for different n values:

For (n) sin (2 π/4) (n) 10 12-1 03 0-14 10 of QAM:n cos (2 π/4)

For (n) Sin (2 π/8) (n) 1 of VSB:n cos (2 π/8)

2 9,0=0 13 4 18,0=1 05

6 27,0=0 17

8 36,0=1 0

Select the frequency relation of fc to fs by selecting suitably, can produce demodulation angle, this can easily realize by looking into very little table.As implied above, under the situation of QAM, can have only 5 different value by the value of 8 Sine and cosine is merged in the 5th row increase by " 1 " of Sine table, and notice, just can from the Sine table, produce cosine by the processing of the Sine pointer in the his-and-hers watches.Like this, for Sine or cosine, QAM need have only the table of 5 values, its value be 0 or ± 1.Similarly, under the VSB situation, for Sine or cosine, need the table of 10 values, its value is 0, ± 1 or

These tables can be stored among the ROM 300, and it is positioned at fixed carrier demodulator table 324, and the mode of selecting according to master microprocessor 400 (VSB or QAM) conducts interviews.If note selecting different IF frequency (not being 37.66MHz), then the size of required table can have significant change.

Selecting S/H sample frequency (fsA) is 43.04MHz, makes that A/D (fsB) sampling clock can be by deriving (21.52Hmz) divided by 2 simply from the S/H clock.Using 21.52MHz is favourable as sampling clock, because be respectively 10.76MHz and 5.38MHz for the character rate of the required system of VSB and QAM.Not only by can easily producing symbol clock speed with 4 or 8 in this way divided by 43.04MHz, and to sample with 2 also be simple.In other words, for VSB or QAM, being handled by the required any character rate of other receiver function (function) must be respectively with 2 or 4 pairs of sampled data stream sampling.Utilize selected sampling rate and character rate, mean for VSB, to abandon in two samplings simply when under the input of required character rate, handling,, then abandon 3 in per 4 samplings simply QAM.If select reasonable (i.e. (n/m) (21.52)) different sampling rate than (rational ratio) of an is-symbol speed, then the input of handling at character rate needs more complicated interpolation/sample process.According to sample/symbol ratio of the present invention, can avoid complicated interpolation/sample process.

Should be appreciated that the present invention can be used for any IF frequency by changing the S/H sampling rate.For example, suppose and need the 44MHz of use standard IF filter to replace 37.66MHz filter 16.At this moment S/H must be with the sample frequency operation (promptly adding 5.38MHz on the centre frequency of IF filter 16) of 49.38MHz.Its result should provide and the similar frequency spectrum at the S/H output shown in Figure 3.AALPF output this moment can be at 21.52MHz speed down-sampling.But, the shortcoming of this moment is that 21.52 and 49.38 can not be simple such as associating for 43.04 and 21.52 2: 1 of setting by one.Use such ratio will increase the complexity of clock generating circuit.In addition, such ratio also increases the unsteadiness of sampling clock.

Thereby in using system of the present invention, best (though and nonessential) is set at 37.66MHz to the centre frequency of IF filter 16.This filter is not a standard.But existing technology allows to design this filter with the method for surface acoustic wave (SAW) filter.

In addition, if the NTSC TV and the digital HDTV of for example simulating in same television set exist simultaneously, can be with the 43.04MHz S/H that samples, this is because the interference that the 44MHz IF frequency of current use can be expected in the NTSC TV signal of simulation.Do not make it be suitable for digital IF frequency 37.66MHz if do not wish the NTSC IF frequency that changes simulation, then can adopt the voltage-controlled quartz oscillator of 75.334MHz, after being removed, then produce the S/H sampling rate of 37.66MHz by 2.This frequency (75.334MHz) no longer conforms to the NTSC IF frequency range of simulation.In addition,,, then must change into 32.39MHz, so that obtain the AALPF frequency spectrum among Fig. 3 if do not use the IF frequency of 37.66MHz for digital HDTV.At this moment, the sampling clock of generation 21.52MHz needs one 2/7 times multiplier to multiply by main frequency of quartz oscillator (being 75.334MHz).This is compared to the sampling of 43.04MHz and keeps speed more complicated divided by Z simply, and can cause the unsteadiness that sampling clock is bigger.

In the system of Fig. 2, AGC control 40 is obtained by the IF circuit of simulation and the combination of digital AGC piece 322, and piece 322 is positioned at the back of A/D converter 52.The IF circuit replenishes as AGC's, because if there is not IF AGC control, then A/D converter 52 can occur saturated and cause problem.Make in this way and use the digital AGC method to compare fully, need an AGC again and the delay that causes than short.

As shown in Figure 4, use system of the present invention can use another kind of scheme for circuit 50.Here it is uses the A/D converter of 43.04MHz, and it has itself inside sampling and holding circuit and digital translation with the 43.04MHz operation.For example, the converter circuit in Fig. 4 501 will replace the converter circuit 50 among Fig. 2.In Fig. 4, connect the output of amplifier 18 at the input (H) of the ADC 521 of N position, be used for receiving IF signal elm, and the output of its N position (P) delivered to the input of Hibert filter 328.Notice that this structure does not need AALPF or the outside S/H among Fig. 2, does not need the AALPF 28,31 among Fig. 1 yet.This is because Fig. 4 has only a sampling processing, and has two among Fig. 2.But, the ADC 521 of Fig. 4 must be with the twice operation of the frequency of the ADC among Fig. 2 52.Timing recovery circuit 321 provides the synchronous sampling signal of 43.04MHz to ADC 521.

By the IF signal elm of ADC 521 sampling is the IFOUT signal of 6MHz bandwidth shown in Figure 3, and its centre frequency is 37.66MHz, and upwards expansion+3MHz reaches 40.66MHz, subtracts 3MHz downwards and becomes 34.66MHz.

Frequency sampling IF signal by with 43.04MHz just produces a signal band, and its centre frequency is-5.38MHz ,-8.07MHz and-expand between the 2.69MHz.The applicant thinks that the IF frequency component of " bearing " produces a mirror image, and it is between 2.69MHz and the 8.07MHz, and centre frequency is 5.38MHz.In addition, utilize 43.04MHz to sample and form other repetition, shown in waveform S/H OUT among Fig. 3.Referring to Fig. 2, because first sample frequency is 43.04MHz, second is sampled as 21.52MHz again, so must remove the analog energy in addition at 10.76MHz by means of AALPF 53.In contrast, in the system of Fig. 4, only under 43.04MHz, sample, since not obvious at the aliasing of S/H OUT, so do not need AALPF.Like this, for the structure of Fig. 4, because have only a sampling processing, so the frequency spectrum of being represented by S/H OUT is actually the frequency spectrum of the output of A/D converter.In addition, (1/2 (43.04=21.52MHz) be not so there is significant aliasing because there be not about 1/2 sample frequency overlapping.

The applicant also finds, in order to satisfy the nyquist criterion and to produce the required bandwidth signal of waveform S/H OUT shown type among Fig. 3, ADC 521 needn't be to double the highest frequency sampling of 40.66MHz.

Be important to note that in using system of the present invention and circuit, what be sampled is the IF signal, and like this, only needing the one the second local oscillators and two frequency mixers to come IF input signal down converted is midband, then to this IF band sampling, so that relevant I, the Q signal of demodulation.Important also is, notices that I, Q signal produce by same circuit, thereby the phase place of I, Q signal is not subjected to along the influence of the different component values of different paths with amplitude.

Claims

1. a radio frequency (rf) receiver comprises:

Be applicable to the input terminal of one or several signal in the rf input signal that is used for receiving many different digital modulation;

Conversion equipment with input and output;

The input of described conversion equipment is connected to the device of described input terminal, is used for down converted rf input signal and produces intermediate frequency (IF) signal at the output of described conversion equipment; And

Sampling apparatus has input with the output of described conversion equipment and is used for the digital sample intermediate-freuqncy signal, and has and be used for responding the output that the rf input signal produces baseband signal.

2. radio frequency as claimed in claim 1 (rf) receiver, wherein said input terminal is applicable to one or several signal in the input signal that receives many different digital modulation, comprising quadrature amplitude modulation (QAM) and residual sideband (VSB) rf input signal; And

Wherein said sampling apparatus comprises that being used for responding QAM rf input signal produces homophase (I) baseband signal and quadrature (Q) baseband signal at its output, and response VSB rf input signal produces the device of homophase (I) baseband signal.

3. radio frequency as claimed in claim 1 (rf) receiver, wherein said receiving system comprises:

First frequency mixer and second frequency mixer, each frequency mixer have an input and an output;

First local oscillator (LO1) and second local oscillator (LO2), each local oscillator has an output, is used for producing frequency signal;

Be used for the output of LO1 and rf input signal are connected to the device of the input of first frequency mixer;

Being used for the output of first frequency mixer is connected to and having first centre frequency (fc1) and bandwidth is the input of first band pass filter (BPF1) of Bhz, is the device of first output signal (fo1) of Bhz for the fc1 bandwidth thereby produce centre frequency at the output of BPF1;

Be used for the output of the output of BPF1 and second local oscillator is connected to the input of second frequency mixer so that the device of down conversion rf signal; And

Be used for the output of second frequency mixer is connected to the device of the input of second band pass filter (BPF2); Described BPF2 has only second centre frequency (fc2) and bandwidth B hz, and BPF2 has the output of the output that is used for limiting first conversion equipment, produces intermediate-freuqncy signal at this output, and its centre frequency equals fc2, and its bandwidth equals Bhz.

4. radio frequency as claimed in claim 1 (rf) receiver, sampling apparatus wherein comprises:

Sampling and holding circuit (S/H) with input, output and input end of clock;

Low pass filter with input and output; And

Analog to digital converter (ADC) with input, output and input end of clock;

The input of S/H is connected to the output of conversion equipment, and the output of S/H is linked the device of the input of low pass filter;

The output of low pass filter is connected to the device of the input of ADC; And

Being used for input end of clock to S/H provides and has frequency for the sampled signal of f3 and be used for input end of clock to ADC frequency is provided is the device of f4, and wherein f3 is the multiple of the rational of f4.

5. radio frequency as claimed in claim 4 (rf) receiver, wherein frequency f 3 is 2 times (being f3=2f4) of frequency f 4.

6. radio frequency as claimed in claim 1 (rf) receiver, wherein said sampling apparatus comprises a unique independent analog to digital converter (ADC), it has output and the input that is connected to described first conversion equipment, is used for the described IF signal of digital sample and produce baseband signal.

7. radio frequency as claimed in claim 1 (rf) receiver, sampling apparatus wherein comprises analog to digital converter (ADC), it has signal input port, signal output port and the input end of clock that is used for applying sampled signal; And

The signal input port of ADC wherein is connected to the output of conversion equipment, and the signal output port of ADC is connected to signal demodulator circuit.

8. radio frequency as claimed in claim 2 (rf) receiver, wherein said conversion equipment comprises:

First frequency mixer and second frequency mixer, each frequency mixer has input and output,

First local oscillator (LO1) and second local oscillator (LO2), each local oscillator has the output that is used for producing a frequency signal;

The output of LO1 and rf input signal are connected to the device of the input of first frequency mixer;

The output of first frequency mixer is connected to has first centre frequency that (input of first band pass filter (BPF1) of fc (1) and bandwidth B hz is used for producing at the output of BPF1 the device of first output signal (fo1) with the first centre frequency fc1 and bandwidth B hz;

The output of the output of BPF1 and LO2 is connected to the input of second frequency mixer, is used for the device of down conversion rf signal; And

The output of second frequency mixer is connected to the device of the input of second band pass filter (BPF2); Described BPF2 has second centre frequency (fc2) and bandwidth B hz, and has the output of the output that limits first conversion equipment, is used for producing intermediate-freuqncy signal thereon, and its centre frequency is fc2, and its bandwidth is Bhz.

9. radio frequency as claimed in claim 8 (rf) receiver, sampling apparatus wherein comprises:

Sampling and holding circuit (S/H) with input, output and input end of clock;

Low pass filter with input and output; And

Analog to digital converter (ADC) with input, output and input end of clock;

The input of S/H is connected to the output of first conversion equipment and the output of S/H is connected to the device of the input of low pass filter;

Clock input to S/H provides sampled signal with frequency f 3 and the device that the sampled signal with frequency f 4 is provided to the clock input of ADC; And wherein f3 is the reasonable multiple of f4.

10. radio frequency as claimed in claim 9 (rf) receiver, receiver wherein, wherein frequency f 3 is twices (being f3=2f4) of frequency f 4.

11. radio-frequency transmitter as claimed in claim 9, wherein the centre frequency of first band pass filter signal frequency that deducts the output of second local oscillator that links to each other with second frequency mixer equals the centre frequency of second band pass filter.

12. radio-frequency transmitter as claimed in claim 1, the sampled signal frequency that wherein is added on the S/H circuit be equal to or greater than centre frequency f2 add frequently fA's and, wherein fA equal the QAM signal bandwidth half or equal half of VSB signal bandwidth.

13. radio-frequency transmitter as claimed in claim 12, wherein the input of a Hilbert filter is linked in the output of ADC, is used for producing at the output of Hilbert filter the real part and the imaginary part of sampled signal.

14. radio-frequency transmitter as claimed in claim 13, wherein the output of Hilbert filter is added on the demodulator, be used for responding the QAM input signal and produce I, Q baseband signal, and response VSB rf input signal produces the I baseband signal.

Be used for the digital demodulation carrier signal and finish the device that received signal is converted to base band at the output of demodulator 15. radio-frequency transmitter as claimed in claim 14, demodulator wherein comprise.

16. radio-frequency transmitter as claimed in claim 15, wherein the centre frequency of BPF2 is selected like this, make the sample frequency be added on the S/H circuit be equal to or greater than fc2 add frequency f A's and; Wherein fA is half of QAM signal bandwidth or half of VSB signal bandwidth.

17. radio-frequency transmitter as claimed in claim 13 wherein also comprises the device of the frequency that is used for adjusting second local oscillator; The described device that is used to adjust comprises local oscillator adjustment circuit, and it has the output of the output that is connected in the Hihbert filter and is connected in an output of second local oscillator, is used to adjust its frequency.

18. radio-frequency transmitter as claimed in claim 9, wherein said sampling apparatus comprises a unique independent analog to digital converter (ADC), be connected to the output of BPF2, be used for near the described IF signal of the frequency sampling of fs, wherein the fs centre frequency (fc2) that equals second band pass filter add frequency f A's and, wherein fA is half of QAM signal bandwidth or half of VSB signal bandwidth.

19. radio-frequency transmitter as claimed in claim 9, sampling apparatus wherein comprise have input port, the analog to digital converter (ADC) of output port and input end of clock, on its input end of clock, apply sampled signal;

Wherein the signal input port of ADC is connected to the output of BPF2, and the signal output port of ADC is connected to demodulator circuit; And

Sampling apparatus wherein comprises that the input end of clock to ADC provides the device of sampled signal, the centre frequency (fc2) that the frequency of described sampled signal is equal to or greater than second band pass filter add a half-band width of QAM signal or add the VSB signal a half-band width and.

20. radio-frequency transmitter as claimed in claim 9, wherein said sampling apparatus comprises analog to digital converter (ADC), it has the signal input part of the output that is connected to BPF2, signal output part and input end of clock, sampled signal wherein is added to input end of clock, so that add the frequency (fs) of the frequency sum of the B/2Hz described signal of sampling at this input with the centre frequency (fc2) greater than BPF2.

21. radio-frequency transmitter as claimed in claim 20, wherein the output of ADC is connected to the Hilbert filter, in order to producing first signal of representation signal real part at first output, and produces the secondary signal of the imaginary part of representation signal at its second output.

22. a radio frequency (rf) receiver comprises:

Be suitable for receiving the input terminal of one or several signal in the rf input signal of many different digital modulation, described input signal comprises quadrature amplitude modulation (QAM) and residual sideband (VSB) rf input signal;

Have first converter apparatus of input and output side, the input of described first converter apparatus is connected on the described input terminal, and described first converter apparatus is used for down converted rf signal and produce intermediate-freuqncy signal at its output; And

Have the device of second conversion of input and output side, its input is connected to the output of first converter apparatus; Described second converter apparatus is used for digital sample intermediate-freuqncy signal and respond described intermediate-freuqncy signal and produce homophase (I) baseband signal at its output, and response QAM rf signal produces quadrature (Q) baseband signal, and response VSB rf signal produces homophase (I) baseband signal.

23. a radio frequency (rf) receiver comprises:

Be suitable for receiving the input terminal of one or several signal in many rf input signals of differently modulating, described input signal comprises quadrature amplitude modulation (QAM) and residual sideband (VSB) rf input signal;

First conversion equipment with input that is connected in described input terminal is used for the described rf input signal of down converted, and has an output, is used for producing intermediate-freuqncy signal thereon; And

Second conversion equipment with input of the output that is connected in first conversion equipment, described second conversion equipment comprises sampling apparatus and demodulating equipment, is used for digital sample intermediate-freuqncy signal and be used for producing baseband signal corresponding to the specific rf input signal that receives.

24. radio frequency (rf) receiver that is applicable to one or several signal in the rf input signal that receives many differently modulation, described input signal comprises (QAM) and residual sideband (VSB) input signal of quadrature amplitude modulation, and described receiver comprises:

First frequency mixer, has an input unit, provide the output of the rf input signal and first local oscillator to it, wherein first frequency mixer has an output, it is applied the input of first band pass filter (BPF1), described BPF1 has first centre frequency (Fc1) and bandwidth B hz, is used for producing first output signal (Fo1) at the output of BPF1, and it has the first centre frequency fc1 and bandwidth B hz;

Be used for second frequency mixer of down converted rf signal, it has input unit, the output of the output of BPF1 and second local oscillator is connected in described input unit, second frequency mixer has the output of the input that is connected to second band pass filter (BPF2), and described BPF2 has second centre frequency (fc2) and bandwidth B hz; BPF2 has the output that is used for producing intermediate-freuqncy signal, and the centre frequency of intermediate-freuqncy signal equals fc2, and bandwidth equals Bhz;

The converter apparatus that comprises sampling apparatus and demodulating equipment is used for sample frequency (fs) sampling intermediate-freuqncy signal, and has the baseband signal of centre frequency fc3 corresponding to the specific rf input signal generation that receives; And

Wherein fc3 and fc2 have a reasonable multiple each other.

25. radio-frequency transmitter as claimed in claim 24, wherein said demodulating equipment comprises the table that a quilt is looked into, and is used for producing homophase (I) and quadrature (Q) baseband signal and responds the value that VSB rf input signal is used for producing the demodulation angle of in-phase base band signal comprising response QAM rf input signal.