Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H11/00—Networks using active elements
  • H03H11/02—Multiple-port networks
  • H03H11/16—Networks for phase shifting
  • H03H11/22—Networks for phase shifting providing two or more phase shifted output signals, e.g. n-phase output
• • 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
  • H03H11/08—Frequency selective two-port networks using gyrators
• • 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
  • H03H11/12—Frequency selective two-port networks using amplifiers with feedback
  • H03H11/126—Frequency selective two-port networks using amplifiers with feedback using a single operational amplifier
• • 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
  • H03H2011/0494—Complex filters

Definitions

• the present invention relates in general to a polyphase bandpass filter.
• Such filters are known per se, for instance from the United States patent 4.914.408, and they can for instance be applied in receiver circuits for, e.g. radio applications, television applications, or telephone applications. Although such filters also know different applications, a possible application of such a filter will be explained here m more detail m the context of a receiver circuit.
• figure 1 schematically shows a known receiver circuit
• figure 2A schematically illustrates the transmission characteristic of a low pass filter
• figure 2B schematically illustrates the transmission characteristic of a bandpass filter, derived from the transmission characteristic of figure 2A
• figure 2C schematically shows a parallel connection of a capacitor and a complex component
• figure 2D schematically illustrates a known way of coupling two filter channels
• figure 3A illustrates the coupling principle according to the present invention
• figure 3B illustrates a replacement representation of the coupling schedule of figure 3A
• figure 4 illustrates a coupling principle according to the present invention
• Figure 1 schematically shows a known receiver circuit 1, in which a receiver signal S coming from an antenna 2 is mixed in a first mixing stage 3 with a signal ⁇ provided by a local oscillator 5, and wherein said signal S is mixed in a second mixing stage 4 with a second signal provided by the local oscillator 5 which is 90° shifted with respect to the first signal ⁇ .
• the output signal of the first mixing stage 3, which is also indicated by the phrase inphase signal, is fed to a first input 11 of a filter 10
• the output signal of the second mixing stage 4 which is also indicated by the phase quadrature signal, is fed to a second input 12 of the filter 10.
• the filter 10 has two filter channels 13 and 14, respectively, which process the inphase signal of the first input 11 and the quadrature signal of the second input 12, respectively, in substantially identical way, and which have outputs 15 and 16, respectively, for providing an inphase output signal and a quadrature output signal, respectively, wherein the quadrature output signal of the second output is shifted 90° with respect to the inphase output signal of the first output.
• the filter channels 13 and 14 have mutual identical filter characteristics, for example a bandpass characteristic.
• the frequency of the local oscillator signal will be indicated by f x .
• the tuning frequency to which the reception circuit 1 must be tuned will be indicated by f 2 . Assume that this frequency is higher than the local frequency f L , i.e. that
• the filter 10 has a bandpass characteristic which is substantially symmetrical with respect to the center frequency ⁇ c .
• Figure 2A schematically illustrates the transfer characteristic of a lowpass filter.
• the frequency ⁇ is set out, and the transfer function H is set out along the vertical axis.
• said lowpass filter can have a desired characteristic, for instance first order, second order, or higher order, Bessel-type, Butterworth-type, etc.
• a bandpass filter can be derived by a transformation or shifting of the filter characteristics to a higher frequency.
• Figure 2B shows the characteristic of figure 2A, shifted over a distance ⁇ c to a higher frequency.
• the transfer function H BDF ( ⁇ ) of this bandpass filter fulfills the following formula:
• H BDF ( ⁇ ) H LDF ( ⁇ - ⁇ c ) (1)
• the desired shift of the filter characteristic corresponds to a shift of all poles and all zeros of the filter over mutually identical distances along the imaginary axis.
• this can be achieved by switching a complex component X in parallel to said capacitive filter components, of which the admittance Y x is a constant complex number according to the formula
• FIG. 2C schematically shows a parallel connection of a capacitor C and such a complex component X.
• Y c of a capacitor with a capacitive value C the following formula applies in the case of an ideal capacitor
• the present invention aims to provide a polyphase bandpass filter wherein the coupling between two filter channels, necessary for achieving the desired frequency shift, is effected without resistors.
• the coupling between two filter channels is effected by means of a voltage-controlled current source.
• a polyphase filter is generally indicated by the reference numeral 20.
• the filter 20 has two mutually identical filter channels 30, which will be indicated with the index I and Q, respectively, for distinction with respect to each other.
• Each filter channel 30 If 30 Q has an input 31 ⁇ , 31 Q and an output 32 x , 32 Q . Since the design of the filter channels 30 ⁇ , 30 Q can be any suitable design, while various constructions for filter channels are known per se, the complete design of the filter channels 30 is not shown in figure 3A.
• one capacitive filter component C ⁇ of the inphase filter channel 30 x is shown in figure 3A, and the corresponding capacitive filter component C Q of the quadrature filter channel 30 x is shown.
• the two capacitive filter components C ⁇ and C Q are coupled with each other by means of two current source couplings 40 QI and 40 IQ connected in anti-parallel.
• the first current source coupling 40 QI comprises a first voltage- controlled current source 41 r of which the output is connected in parallel to the capacitive filter component C ⁇ in the inphase filter channel 30 x
• the second current source coupling 40 IQ comprises a second voltage-controlled current source 41 Q of which the output is connected in parallel with the corresponding capacitive filter component C Q in the quadrature filter channel 30 Q
• the first voltage-controlled current source 41 x is controlled by an output signal of a first voltage detector 42 Q , of which the input is connected in parallel with the capacitive filter component C Q
• the second voltage-controlled current source 41 Q is under control of a second voltage detector 42 ⁇ of which the input is connected in parallel with the capacitive filter component Ci.
• the first voltage-controlled current source 41 x adds to the first filter channel 30 ⁇ a current of which the value depends on the voltage over the capacitive filter component C Q in the second filter channel 30 Q
• the second voltage-controlled current source 41 Q adds to the second filter channel 30 Q a current of which the value depends on the voltage over the capacitive filter component C ⁇ in the first filter channel 30 ⁇ .
• the two current source coupling 40 Q1 and 40 IQ can be mutually identical, although this is not necessary. Important is only, that the proportionality factors between the voltage detected by the voltage detector 42 and the current generated by the current source 41 are mutually identical for both current source coupling 40 QI and 40 IQ ; in other words: important is only that the two current source couplings 40 Q ⁇ and 40 ⁇ Q have mutually identical transfer characteristics.
• each current source coupling 40 QI and 40 IQ is designed for letting the voltage-controlled current source 41 x and 41 Q , respectively, generate a current I_u, ⁇ and I_ U , Q , respectively, of which the current magnitude depends on the voltage V CQ and V CI , respectively, detected by the voltage detector 42 Q and 42 ⁇ , respectively, according to the formulas
• a gyrator 50 has two terminals 51A and 51B.
• the gyrator 50 comprises a first current source coupling not shown in figure 3B, of which terminal 51A is a voltage input and of which terminal 51B is a current output.
• the gyrator 50 comprises a second current source coupling not shown in figure 3B, of which terminal 51B is a voltage input and of which terminal 51A is a current output.
• the two current source couplings each have a proportionality factor G M and G BA , respectively, defined as output current divided by input voltage.
• G M and G BA proportionality factor
• the gyrator will be indicated as a symmetrical gyrator. This can be achieved if both current source couplings are identical, but this is not necessary.
• FIG. 4 shows an example of an implementation of a polyphase filter 100 according to the present invention.
• the polyphase filter 100 comprises an inphase channel 101 ⁇ and a quadrature channel 101 Q , which are mutually substantially identical.
• the channels 10A, 101 Q have inputs 102 Ir 102 Q for receiving an inphase input signal ⁇ ⁇ and a quadrature input signal ⁇ Q , respectively.
• the channels 10A, 101 Q further have outputs 103 ! , 103 Q for outputting an inphase output signal ⁇ ⁇ and a quadrature output signal ⁇ Q , respectively.
• the inputs 102 ⁇ , 102 Q are current inputs, i.e.
• the input signals ⁇ ⁇ and ⁇ Q are current signals; if it is desired that the filter 100 receives voltage signals, voltage-to-current converters can be switched before the inputs 102 ! , 102 Q ; since known per se voltage-to-current converters can be used for this, they will not be described in more detail here.
• the outputs 103 ⁇ , 103 Q are voltage outputs, i.e. the output signals ⁇ i and ⁇ Q are voltage signals; when it is desired that the filter 100 outputs current signals, voltage-to-current converters can be switched after the outputs 103 ⁇ 103 Q ; since known per se voltage-to-current converters can be used for this, these will also not be described in more detail here.
• the channels 101 ⁇ , 101 Q comprise a plurality of N capacities Cii, C2 If C3 lA ... CN ⁇ and C1 Q , C2 Q , C3 Q , ... CN Q , respectively, wherein N ⁇ 2.
• the corresponding capacities Cii and Ci Q always have mutually identical capacity values Ci; for different values of i, the capacity values Ci can be different.
• the corresponding capacities Ci and Ci Q are always coupled to each other by a symmetrical gyrator 106i; the proportionality factors Gi IQ and Gi QI of each gyrator 106i are always equal to l/( ⁇ c -Ci).
• the present invention provides a polyphase filter 20; 100 with to filter channels 30 If 30 Q ; 101 ⁇ , 101 Q for processing an I-input signal ⁇ ⁇ and a Q-input signal ⁇ Q , respectively.
• the filter has at least two capacitive filter components C l7 C Q ; Ci , Ci Q corresponding to each other in the two filter channels 30 ⁇ , 30 Q ; 101 ⁇ , 101 Q , wherein the capacity values C; Ci of these two capacitive filter components CT, C Q ; Cii, Ci Q are substantially equal to each other.
• Said two capacitive filter components Ci, C Q ; Ci x , Ci Q are coupled to each other by means of two current source couplings 40 QI , 40 ⁇ Q ; 106i with substantially equal characteristic, switched anti-parallel.
• a displacement of the filter characteristic over a distance ⁇ c toward higher frequencies is achieved.

Landscapes

• Networks Using Active Elements (AREA)
• Filters And Equalizers (AREA)
• Glass Compositions (AREA)
• Nonmetallic Welding Materials (AREA)
• Iron Core Of Rotating Electric Machines (AREA)
• Filters That Use Time-Delay Elements (AREA)
• Power Conversion In General (AREA)

Priority Applications (5)

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Family Applications (1)

Country Status (10)

Cited By (2)

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• 1999
  • 1999-12-24 NL NL1013951A patent/NL1013951C2/nl not_active IP Right Cessation
• 2000
  • 2000-12-21 US US09/741,014 patent/US6346850B2/en not_active Expired - Lifetime
  • 2000-12-22 AU AU20199/01A patent/AU2019901A/en not_active Abandoned
  • 2000-12-22 DE DE60005561T patent/DE60005561T2/de not_active Expired - Lifetime
  • 2000-12-22 AT AT00983445T patent/ATE250824T1/de not_active IP Right Cessation
  • 2000-12-22 EP EP00983445A patent/EP1247339B1/en not_active Expired - Lifetime
  • 2000-12-22 MY MYPI20006104A patent/MY121473A/en unknown
  • 2000-12-22 WO PCT/IB2000/001975 patent/WO2001048918A2/en not_active Ceased
  • 2000-12-22 CN CN00817695.7A patent/CN1183672C/zh not_active Expired - Fee Related
  • 2000-12-22 JP JP2001548523A patent/JP4763206B2/ja not_active Expired - Fee Related

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