SE521527C2 - Apparatus and method for filtering a received signal - Google Patents

Abstract

An apparatus (10) including a compressive receiver (22) detecting the received signal and a frequency agile filter (60) responsive to the compressive receiver (22). The frequency agile filter (60) filters the received signal. A method including the steps of detecting the received signal (204), downconverting the received signal to produce a downconverted signal (206), performing a dispersive delay line calculation on the downconverted signal to produce a pulsed signal having a plurality of pulses (208), comparing at least some of the pulses within the pulsed signal to a threshold (210), measuring the time delay of the pulses that exceed the threshold over a predetermined time interval (212), determining a filter frequency based on the time delay of the pulses (214), and filtering the received signal at the filter frequency (216).

Description

30 U.) The LJ to-digital converter corresponds to the frequency-moving filter and the other analog-to1-digital converter corresponds to the attenuation set. The attenuation rate corresponds to the received signal and generates an attenuated signal.

The method includes the steps of: detecting the received signal; downconverting the received signal to generate a downconverted signal; performing a scattered delay calculation on the downconverted signal to generate a pulsed signal having a plurality of pulses; comparing the amplitudes of at least some of the pulses within the pulsating signal with a threshold value; measuring a delay for the pulses which have amplitudes exceeding the threshold value over a predetermined time interval; determining a filter frequency based on the time delay; and filtering the received signal at the filter frequency.

The invention itself, together with its intended advantages, will be better understood with reference to the following detailed description, taken in conjunction with the accompanying drawings.

Brief Description of the Drawings Fig. 1 is a block diagram of a preferred embodiment of a device for filtering a received signal.

Fig. 2 is a block diagram of another preferred embodiment of a device for filtering a received signal.

Fig. 3 is a flow chart of a preferred embodiment of a method for filtering a received signal.

Detailed Description of the Preferred Embodiments Fig. 1 illustrates an apparatus 10 for detecting and filtering a received signal. The device 10 includes an antenna 12, an input bandpass filter 14, a divider 16, a compressing receiver 22, and a frequency filter 60. The input filter 14 is connected to the antenna 12. and the divider 16. The device 10 also comprises a signal track connected to the divider 16 comprising an amplifier 40, a filter 42, a mixer 44 with a local oscillator 46, a second amplifier 48, a second filter 50, 52, a third filter 54 and a delay circuit 57. a third amplifier The compressing receiver 22 is connected to the divider 16 via a mixer 18 with a local oscillator (LO) frequency moving filter 60 via digital components inside 11 and an attenuator link 20 and is connected to the socket by a threshold comparator 32, a counter 34, a digital controller 36, and a digital-to-analog converter 38. The timing of the compressing receiver 22 is controlled by a time base 30. The compressed receiver 22 is includes a mixer 24, a sweeping local oscillator 26, a dispersive delay line 28 and a weighing filter 29.

During operation, an input radio frequency (RF) signal 13 is received by the antenna 12, filtered by the filter 14 and divided by the divider 16. A first part of the divided signal from the divider 16 is mixed by the mixer 18 with LO 11; damped by the damping set 20; and fed to the compressing receiver 22. A second portion of the split signal from the divider 16 is fed to the first amplifier 40, filtered by the filter 42, mixed by the mixer 44 with an output signal from the local oscillator 46, is amplified by amplifiers 48 and 52, and is filtered by filters 50 and 54 to provide a resultant signal. It will be appreciated, however, that several alternative configurations of filters and amplifiers may be used, such as a single filter and a single amplifier, although the series arrangement illustrated in Fig. 1 provides a desired sensitivity and a desired dynamic range for the receiver 10. The resulting signal delay by a delay circuit 57 and fed to the frequency moving filter 60. The frequency moving filter 60 is controlled by the digital-to-analog converter 38 which responds to the compressing receiver 22. An output signal from the frequency moving filter 60 is converted to a digital signal by analog (ADC) signal 64. Further processing is then performed on the output to digital converter 62 and transmitted as the output signal 64 as digital inverse filtering of the output signal 64. using a digital filter corresponding to the digital unit 36. Other further processing of the output signal 64 includes digital down-conversion ng, filtering and demodulation.

After the received signal 13 has been detected by the antenna 12, downconverted in frequency by the mixer 18, and attenuated by the attenuator set 20, the compressing receiver 22 performs a dispersive delay line calculation on the downconverted signal to generate a pulsed signal having a plurality of pulses. Each of the pulses has a height corresponding to a signal strength and a location corresponding to the frequency of the received signal 13. The compressing receiver 22 performs a real-time Fourier transform on the downconverted signal and provides the output pulsed signal.

The compressed receiver 22 mixes the downconverted signal with a fast sweeping local oscillator signal from the sweep oscillator 26 to generate a frequency modulated (FM) waveform. The scattered delay line 28 compresses each carrier in the downconverted signal into a narrow time range pulse. The weighing filter 29 adds a weighing filter operation to the pulsed signal to better define and reproduce pulses in the pulsed signal.

A time delay for each output pulse relative to the start of the local oscillator sweep is related to the frequency of a carrier in the downconverted signal.

Since the output pulsed signal from the Weighing Filter 29 is proportional to the input power of the detected radio frequency (RF) input signal 10, the threshold comparator 32 can be used to select an input frequency to filter based on the amplitude of the pulses in the pulsed signal. The threshold comparator 32 compares at least some of the pulse amplitudes within the pulsed signal with a threshold value.

The counter 34, preferably a multiple case counter, determines where the pulses occur in time related to a start time of the sweeping LO 26 using a time base 30.

The digital controller 36 then determines a filter frequency by converting the counter output to a digital word. The digital word is converted to an analog control signal by a digital-to-analog converter 38, and the frequency moving filter 60 filters the received signal at the filter frequency set by the digital control unit 36. Preferably, the digital control unit 36 determines the filter frequency using a table to plot the measured time delay to the respective filter frequency. The counter 34 is started at the beginning of a sweep of LO 26 and the output signal of the counter is read by the digital unit 36 when the threshold value is exceeded. Counter 34 is then reset when the sweep is complete. Preferably, the digital controller 36 comprises a controller, such as a HCl6 type controller from Motorola Inc., comprising a processor and a memory.

Depending on the time involved between receiving a signal at the compressing receiver 22 and transmitting a filtered frequency to the frequency affected filter 60, the second divided signal from the divider 16 is preferably delayed in time by a delay 57 so that it second split signal when the frequency-affected filter is away from the digital-to-analog converter 38. At 60 at substantially the same time as the control signal, in this way, the frequency-influencing filter 60 filters the receiving signal at the frequency calculated by the digital unit 36.

In the specific embodiment illustrated in Fig. 1, the circuit 10 must be constructed with the following components: A 15 L 25 5 (AJ LD 521 527 6 The filter 14 is a Filtronix CB285 filter, the divider 16 is a Mini Circuits ZFSC-2- 2-type splitter, mixer 18 150 mixer, and LO11 is preferably a Panasonic ENF-VA7 series type oscillator set to around 880MMZ is an Andersen Laboratories CR-72-12-15 compressor is a Mini Circuits ZFM - The compression receiver 22 is a receiver, and the threshold value comparator 32 is an AD9696 type comparator from Analog Devices.The time base 30 is a US-685-120 type time base from US Crystal Corp. The counter 34 is an ICM 7216B1P1 type counter from Harris Semiconductor, the digital the unit 36 is a Motorola MC68HC16Z1, and the digital-to-analog converter 38 is a Burr Brown DAC600.The amplifier 40 is a pair of Anzac AMC155 type amplifiers in series, the filter 42 is a Filtronix CB286 filter, the mixer 44 is a Watkins Johnson WJ -4020- and the local oscillator 4 6 is an ENF-VA7-Series type oscillator set to around 930 MHz from Nasonic Mixer. Amplifier 48 is a Cougar AC379 amplifier, filter 50 is a Networks International D318 filter, amplifier 52 is a pair of series connected Cougar AP148 and amplifiers. Filter 54 is a Networks International D319 filter. The analog-to-digital converter 62 is an Analog Devices AD9042 converter. The frequency affected filter 60 is a comb filter such as a filter which may be constructed as described in a Milcom article "Novel Active RF Tracking Notch Filters for Interference Suppression in HF, VHF and UHF Frequency Hopping Receivers", Conference Record 1991 IEEE Military Communications Conference Vol 3, page 956, by Masood Ghadaksak (1991).

The preferred method and apparatus for detecting and filtering a received RF signal has many advantages. For example, the preferred embodiment has an improved dynamic range for protecting hardware components, such as analog-to-digital converters 62 from large saturated signals. In addition, the preferred embodiment can be used in multiple access systems such as 10 TD (TDMÅ) f and frequency division multiple access code division multiple ac (FDMA) systems. time division multiple access (CDMA), The preferred embodiment can be used over a wide range of RF frequency bands because the input signal is mixed to a suitable compressed receiver input frequency. However, it should be understood that although the preferred embodiment is particularly suitable for use with cellular frequencies, the present invention is not limited to RF cellular frequency bands.

Furthermore, many conventional methods for limiting the signal level to a receiver detector, such as an ADC, can (S / N) the behavior of the receiver and thereby reduce the sensitivity of the receiver. degradation signal-to-noise In contrast, the preferred embodiment allows processing of RF signals over the entire dynamic range of the cellular band without degrading the S / N behavior.

In addition, the preferred embodiment provides automatic frequency control of the frequency moving filter 60. Since the frequency affected filter 60 is capable of being tuned over the desired reception band, fixed cam filters are not needed and the frequencies to which the filter 60 is tuned can normally be processed as soon as the signal the level is increased above the threshold comparator level.

Another embodiment of the present invention is shown in Fig. 2. The same reference numerals are used for similar components in the two figures. As shown in Fig. 2, the apparatus 100 is similar to the circuit of Fig. 1, but also includes an attenuator set 70 and a second analog-to-digital converter 72 connected to the attenuator set 70. The attenuator set 70 corresponds to the receiving signal 13 and is connected to the delay 57. The value of a threshold value for the attenuator set 70 is selected so that the largest signal obtained by the antenna 12 is processed by an analog-to-digital converter 72 without saturation of the converter 60 protecting the first In this embodiment, the first analog-to-digital-analog-to-digital converter 62 treats from saturation. The converter 62 processes lower level signals and the other analog-to-digital converter 72 processes higher level signals. Thus, the second analog-to-digital converter 72 is capable of processing signals with frequencies which correspond to the frequencies filtered by the frequency moving filter 60.

In a broadband multi-carrier environment where an ADC processes multiple RF input signals, multiple comb filters placed in front of the receiver ADC 62 protect it from saturation of the largest signals. This allows signals with lower levels to be processed by the ADC 62. The value of the threshold value that sets the attenuator set 70 is preferably selected so that the largest signal to the antenna input 12 can be processed by the ADC 72 without measuring it.

In Fig. 2, an RF input signal is applied to two separate tracks: one to the compressing receiver 22 and a second to the low level receiver portion starting with the amplification stage 40. A third stage is provided after the delay 57 and is fed to the threshold attenuation set 70.

The three tracks can be connected to an antenna input, a multiplexer antenna input, or can be replicated in a plurality of receiver parts. The compression receiver 22 performs a real-time Fourier transform representation of its input signals and provides an output pulse for each input signal. The input signal of the compressed receiver 22 is mixed with a fast sweeping LO 26, thereby generating an FM waveform at the mixer output 24. The dispersion delay line (DDL) 28 is used to compress each input signal into a narrow pulse in the time range. The weighing filter 29 forms the output pulse from the DDL 28 to extend the dynamic range of the compressing receiver 22. The weighing filter 29 may be comprised of the DDL structure 28. The current pulse referring to the start of the LO sweep is related to the frequency of the compressing the input signal of the receiver 22. Since the output pulse of the amplitude of the weighing filter 29 is proportional to the power of the detecting input signal, a threshold comparator 32 is used to select the input frequency to be filtered. based on its amplitude.The combination of amplitude and time delay information is then converted to a bias voltage for the frequency moving filter 60.

One method of performing the conversion is to use a multiplier 34 to correlate the input signal to the detected frequency. This is accomplished by starting the counter 34 at the beginning of the sweep, reading a count value when the amplitude threshold value is exceeded, and resetting the counter 34 when the sweep is completed. The counter output is read by the digital controller 36 and used for either an analog voltage or a digital word depending on the filter control requirements of the filter 60.

Using multiple adjustable cam or band stop filters, the ADC 62 is essentially protected from multiple large input RF signals. The delay block 57 allows the compression receiver 22 to detect and control the filter 60 before the ADC 62 becomes saturated. The RF signals below a predefined power level threshold are processed by the ADC 62. Large RF signals above this threshold level are processed by the ADC 72 which is protected by the input threshold setting attenuation set 70. Thus, in the preferred embodiment, using multiple analog digital converters 62 and 72, the dynamic range of the entire receiver 10.

A preferred embodiment of a method for filtering a receiving motion frequency signal is illustrated in Fig. 3. As shown in Fig. 3, the method 200 begins at 202 and includes the steps of detecting the received signal, step 204; downconverts the received signal to generate a downconverted signal, step 206; performing a dispersion delay line calculation on the downconverted signal to generate a pulsed signal having a plurality of pulses, step 208; comparing the amplitudes of at least some of the pulses within the pulsed signal with a threshold value, step 210; measuring a delay of the pulses which have amplitudes exceeding threshold steps 212; determining a filter frequency based on the time delay over a predetermined time interval, step 214; and filtering the received signal at the filter frequency, step 216. The step of determining file step 216, bell to plot the number of pulses counted with the filter frequency, may use a look-up rate. In addition, the method may further comprise the additional steps of applying a weighting filter to the pulsed signal or delaying the received RF signal for filtering the received signal at the filter frequency.

It is to be understood that for the purpose of this application, a second component is equivalent to or in communication with a first component whether or not the first and second components are directly interconnected or indirectly interconnected such as via intermediate components, including switches which operationally can interconnect the components for only part of the time, as long as the signal track can be directly or indirectly and establish a relationship between the components.

For example, the frequency moving filter 60 is corresponding to the compressing receiver 22, as defined herein, such as the comparator 32, and D / A 38, between the compressing receiver 22 and the filter 60. although intermediate components, the counter 34, the controller 36, are provided. Advantages and modifications of the above-described device and method will become apparent to those skilled in the art. For example, although the digital controller 36 generates a digital word in the preferred embodiment, the digital controller 36 may alternatively generate an analog voltage to control the filter 60 depending on specific filter requirements. In addition, although the operation of the preferred embodiment was described using two analog-to-digital converters, the present invention is not limited to the number of analog-to-digital converters used.

The invention, in its broader sense, is therefore not limited to the specific details, representing the device, and the illustrative examples shown and described above. Various modifications and variations may be made to the above specification without departing from the spirit or spirit of the present invention, and it is intended that the present invention cover all such modifications and variations provided within the scope of the following claims and their equivalents. lenter.

Claims (10)

lO 15 20 25 30 521 527 P A T E N T K R A V An apparatus for filtering a received RF signal comprising: a compressing receiver for receiving the received RF signal and generating a pulsed signal; means for comparing pulses within the pulsed signal with a threshold value and determining a filter frequency based on a time delay of the pulses exceeding the threshold value, and generating an analog control signal indicating the filter frequency; a frequency agile filter for receiving the control signal and filtering a delayed received signal at the filter frequency. An apparatus according to claim 1, wherein the compressing receiver comprises a mixer, a dispersion delay line module, and a weighing filter; and the mixer is corresponding to the received signal, the dispersion delay line module is corresponding to the mixer and the weighing filter is corresponding to the dispersive delay line module. The device according to claim 2, wherein the compressing receiver further comprises a sweeping local oscillator unit connected to the mixer. An apparatus according to claim 1, further comprising an analog-to-digital converter corresponding to the frequency moving filter. 70569 amended requirements.doc; 2003-04-25 lO l5 20 25 30 521 527, H ,, =, ¿: ¿¿,, M ß 2 m: 1 '_, = The device of claim 4, further comprising a bandpass filter in conjunction with the frequency moving filter and the compressing receiver. The apparatus of claim 1, further comprising: a frequency agile filter corresponding to the received RF signal and generating a filtered signal; a first analog-to-digital converter corresponding to the frequency moving filter; an attenuator set corresponding to the received RF signal and generating an attenuation signal; and a second analog-to-digital converter corresponding to the vapor charge. Device according to claim 6, further comprising a control unit in cooperation with the frequency-moving filter. Device according to claim 7, further comprising a compressing receiver in cooperation with the control unit. A method of detecting and filtering a received signal comprising the steps of: detecting the received signal; downconverting the received signal to generate a downconverted signal; performing a dispersive delay line calculation on the downconverted signal to generate a pulsed signal having a plurality of pulses; comparing the amplitudes of at least some of the pulses within the pulsed signal with a threshold value; 70569 amended requirements.doc; 2003-04-25 measuring a time delay for the pulses having an amplitude which exceeds a threshold value over a predetermined time interval; determining a filter frequency based on the time delay; and filtering the received signal at the filter frequency. 10. l0. A method according to claim 9, further comprising the step of applying a weighing filter to the pulsed signal. 70569 changed requirements.dOC7 2003-04-25