Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/201—Filters for transverse electromagnetic waves
  • H01P1/203—Strip line filters
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H11/00—Networks using active elements
  • H03H11/02—Multiple-port networks
  • H03H11/04—Frequency selective two-port networks
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/201—Filters for transverse electromagnetic waves
  • H01P1/203—Strip line filters
  • H01P1/2039—Galvanic coupling between Input/Output

Definitions

• the present invention relates to an improvement to the band rejection filter or active stop-band filter.
• the invention is applicable to transmission and / or reception systems meeting the DVB-H (for Digital Video Broadcasting - Handheld) or DVB-T (for Digital Video Broadcasting - Terrestrial) standards.
• the invention is more particularly applicable in fixed or mobile digital television receivers, in particular responding to the DVB standard for filtering interfering signals, such as, for example, WIMAX signals (for Worldwide Interoperability for Microwave Access), present in the frequency band called digital dividend band.
• WIMAX signals for Worldwide Interoperability for Microwave Access
• the digital dividend represents the frequency resources that will be released when switching from analogue to digital television broadcasting.
• the digital dividend band is different in different parts of the world and, for example, between 698 MHz and 862 MHz for the Americas and 790 MHz and 862 MHz for the Europe / Asia region, as shown in Figure 1.
• WIMAX signals may saturate the DVB receiver.
• WIMAX signals must be filtered in different bands depending on the region. However, it is known that the signal must be attenuated in a 10 MHz wide band and the WIMAX signal must be rejected by 42dB. There are therefore cases where the WIMAX transmitter will not be present and where a filter will not be useful.
• the filtering of these disturbing signals can be carried out using a suitable band rejection or band-stop filter.
• a suitable band rejection or band-stop filter it is known to use a half-wave line resonator filter as shown in FIG. 2, which is sized to resonate at a high frequency, well above the useful frequency.
• the filter of Figure 2 comprises a transmission line LT ( ⁇ , ⁇ , k) to which is coupled a resonator ⁇ / 2 RE.
• LT transmission line
• ⁇ ⁇ , ⁇ , k
• the energy from the transmission line is "absorbed" by the resonator thereby creating a theoretically infinite attenuation in a relatively narrow band around the resonant frequency.
• this filter has the disadvantages of having losses that significantly degrade the rejection. It is more cumbersome and difficult to tune in central frequency.
• the negative-resistance circuit consists of a transistor Q1 whose base is connected to the resonator RE and whose collector is connected to a series LCR circuit. As shown in the right part of FIG. 4, this circuit is equivalent to a resistance Rneg in parallel with a capacitance Ceq.
• This circuit allows an easy agreement of the value of the load capacity thanks to a simple bias voltage, while ensuring the compensation of losses of the filter which ensures a high quality factor.
• FIG. 5 which gives, as a function of frequency, the transmission (curve a) and the rejection (curve b) of the filter. These curves show a very strong rejection (> 42 dB) at the center frequency of the filter around 700 MHz. The latter can be tuned by a simple adjustment of the bias voltage.
• the present invention provides a filter of the type described above that can be deactivated.
• the filter thus obtained can be inserted in series in the reception chain.
• the resonator When the resonator is charged by an active capacitance, it can be tuned to the particular frequency to reject whatever region is considered and can be disabled if necessary. It becomes transparent from a system point of view and does not consume energy.
• the present invention therefore relates to an active band-stop filter comprising a filter input and a filter output connected by a transmission line, a resonator coupled to the transmission line and connectable to a load impedance, characterized in that it comprises means for activating the filtering function in a selected operating band.
• the activation means of the filtering function is performed by a switch positioned between one end of the resonator and the load impedance.
• the load impedance may be constituted by a capacitance, a varactor diode for tuning the operating frequency or a negative resistance circuit simulating an active capacitance further ensuring a compensation of the losses of the filter.
• the means for activating the filtering function is provided by a PIN diode positioned between one end of the resonator and the passive capacitance.
• the activation means of the filtering function is performed by the supply voltage of the transistor making it possible to realize the active capacitance.
• FIG. 2 already described schematically represents an embodiment of a band-stop filter to which the invention can be applied.
• FIG. 5 represents the transmission and rejection curves obtained by simulating the band stop filter of FIG. 2 loaded by an active capacitor.
• FIG. 6 represents a band-stop filter according to the present invention according to a first embodiment.
• FIG. 7 represents the response of the filter of FIG. 6 when the switch is in open circuit
• FIG. 8 represents the transmission and reflection response of the filter when the switch is in a closed circuit
• FIG. 9 represents another embodiment of a band-stop filter according to the present invention.
• FIG. 10 represents yet another embodiment of a band-stop filter according to the present invention.
• Figure 1 1 shows another alternative embodiment of a band stop filter according to the present invention.
• the band stop filter or band rejection filter is constituted by a transmission line LT having an input A and an output B.
• a resonator RE is coupled with the transmission line LT. It is a section of line of length less than ⁇ / 2, ⁇ representing the guided wavelength at the rejection frequency of the filter.
• One end of the resonator is connected to ground. The other end is connected to a means for activating the filter function formed in the illustrated embodiment by a switch CM that can switch between a DC terminal connected to a load impedance and an unconnected CO terminal.
• the load impedance is constituted by a negative resistance circuit simulating an active capacitor such as the circuit of FIG. 4.
• the negative resistance circuit is an active component well known to those skilled in the art and whose diagram is illustrated in FIG. 4. It comprises a bipolar transistor Q1 whose base is connected to the resonator RE, whose emitter is connected to ground and whose collector is connected to a charging circuit formed of an inductance L, a capacitor C and a resistor R connected in series with the ground.
• the transistor Q1 is polarized by means known per se (not shown).
• the resonator is in open circuit.
• the band stop filter whose intrinsic length is only 12 mm in the embodiment chosen, thus resonates at a frequency of 3.5 GHz.
• the filter response is completely transparent. The filter behaves like a transmission line that has virtually no loss due to its short physical length as shown in Figure 7. This position is used in the absence of disruptive.
• the switch If the switch is connected to the circuit of the active capacitor, position CC, it returns the resonance of the band stop filter to the UHF band at the frequency to be rejected. It can then be imagined that the DVB-H demodulator to which the filter is connected can manage the sending of the control voltages required for the active band stop filter as a function of the frequency of the detected disturbing channel. In this position, the filter functions as the circuit of FIGS. 3 and 4 and transmission (a) and rejection curves (b) are obtained which are similar to the curves of FIG.
• the means for activating the filter function is achieved by directly connecting the base of the transistor Q1 to one end of the resonator RE and using the supply voltage of the active capacity.
• the supply voltage is equal to the bias voltage Vb of the active capacitance (around 2V for the example provided)
• the tunable rejection filter function (the rejection frequency is determined by the exact value of Vb) is activated.
• the band stop filter is connected to a passive capacitor C and the activation means of the filtering function is constituted by a "switch" switch which can switch between an unconnected CO terminal and a DC terminal connected to the passive capacitance.
• the operation of this circuit is identical to the operation of the switch of FIG.
• the band stop filter is, in this case, connected to a passive capacitance by a PIN diode positioned between one end of the resonator and the passive capacitance.
• a PIN diode When the PIN diode is in the "ON" state, it is equivalent to a short circuit and the resonator is then connected to the load capacity and the filter function is activated.
• the PIN diode When the PIN diode is in the "OFF" state, it is equivalent to an open circuit and the filter function is not activated.
• the band stop filter produced is composed of a transmission line to which is coupled a miniaturized line loaded by an active capacitance, these lines being able to be produced using micro-ribbon technology.
• the active capacitor uses CMS LC components mounted on an FR4 substrate. A prototype of a filter as described above was simulated.
• FIG. 8 shows the transmission and reflection response of the active band stop filter.
• a rejection of at least 40 dB at 700 MHz can be noted.
• Loss of out-of-band insertions are low and do not exceed -0.4 dB.
• the measured noise factor is low and is less than 0.5 dB in the bandwidth of the filter.
• the reflection coefficient at the central frequency of the filter is of the order of -0.1 dB thus guaranteeing the electrical stability of the circuit.
• the filter allows automatic switching of response by a simple activation / deactivation of its bias voltage. It does not therefore require the use of switched input and output filters that can sometimes be cumbersome and cause significant loss of insertions.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Filters And Equalizers (AREA)
• Networks Using Active Elements (AREA)
• Control Of Motors That Do Not Use Commutators (AREA)

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Publications (1)

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• 2011
  • 2011-03-11 WO PCT/EP2011/053684 patent/WO2012079777A1/fr active Application Filing
  • 2011-03-11 EP EP11707860.0A patent/EP2652835A1/de not_active Withdrawn
  • 2011-03-11 KR KR1020137015661A patent/KR20130142160A/ko not_active Application Discontinuation
  • 2011-03-11 US US13/994,241 patent/US9300273B2/en not_active Expired - Fee Related
  • 2011-03-11 CN CN2011800606228A patent/CN103314481A/zh active Pending
  • 2011-03-11 JP JP2013543577A patent/JP5786031B2/ja not_active Expired - Fee Related

Non-Patent Citations (1)

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