Transferred-impedance filtering in RF receivers
View Patent ↗The specification and drawings present a new method and apparatus for using transferred-impedance filtering in RF (radio frequency) receivers (e.g., inside of a mobile communication device), wherein said filtering can be done with MOS-switches transferring impedance of a regular RC or RCL circuit to RF frequency filtering inside an RFIC (radio frequency integrated circuit).
1. A method, comprising:
receiving a radio frequency signal and converting it to an electrical domain;
amplifying said radio frequency signal in said electrical domain using an amplifier having a resistance R on its output, thus generating an amplified radio frequency signal; and
filtering said amplified radio frequency signal using at least one transferred-impedance filter containing at least one capacitor and having a pass band with a center frequency determined by a reference frequency, wherein −3 dB frequencies of said pass band are given by said reference frequency plus a corner frequency which depends on said resistance R and a capacitance C of said at least one capacitor and by said reference frequency minus a further corner frequency which also depends on said resistance R and said capacitance C of said at least one capacitor.
2. The method of claim 1 , wherein said at least one transferred-impedance filter is an amplifier.
3. The method of claim 1 , further comprising:
attenuating by a predefined or variable value the radio frequency signal in a separate channel from said transferred-impedance filter for generating an attenuated radio frequency signal; and
generating a subtraction signal between said filtered radio frequency signal and said attenuated radio frequency signal using a mixer.
4. A receiver, comprising:
an amplifier having a resistance R on its output, configured to amplify a radio frequency signal, and to generate an amplified radio frequency signal; and
at least one transferred-impedance filter, configured to filter said amplified radio frequency signal, said transferred-impedance filter containing at least one capacitor and having a pass band with a center frequency determined by a reference frequency, wherein −3 dB frequencies of said pass band are given by said reference frequency plus a corner frequency which depends on said resistance R and a capacitance C of said at least one capacitor and by said reference frequency minus a further corner frequency which also depends on said resistance R and said capacitance C.
5. The receiver of claim 4 , further comprising:
an attenuator, configured to attenuate by a predefined or variable value the amplified radio frequency signal in a separate channel from said transferred-impedance filter for generating an attenuated amplified radio frequency signal; and
a mixer, configured to generate a subtraction signal between the filtered amplified radio frequency signal and said attenuated amplified radio frequency signal.
6. The receiver of claim 4 , wherein said corner frequency and said further corner frequency are equal and given by F RC =1/π2RC.
7. The receiver of claim 6 , wherein said receiver contains two transferred-impedance filters of said at least one transferred-impedance filter, in inphase and quadrature branches respectively, wherein each of two local oscillator signals having said frequency F LO but π/2 apart in a phase domain is provided to only one of said two transferred-impedance filters.
8. The receiver of claim 4 , wherein said reference frequency is a local oscillator frequency F LO provided to said transferred-impedance filter.
9. The receiver of claim 4 , wherein said at least one transferred-impedance filter is configured to perform a down conversion mixing function such that a low frequency baseband signal is an output signal of said transferred-impedance filter.
10. The receiver of claim 4 , wherein parasitic capacitances of said transferred-impedance filter are compensated by an inductor in the amplifier such that an absolute value of a reactive component of an amplifier output impedance is close to zero and negligible compared to a resistive component of said amplifier output impedance.
11. The receiver of claim 4 , wherein at least one inductor L is added in series or in parallel with said at least one capacitor C and said reference frequency is given by F LO -F LC or F LO +F LC , said F LO being a local oscillator frequency provided to said transferred-impedance filter and said F LC being an LC resonant frequency given by F LC =1/2π√{square root over (LC)}.
12. The receiver of claim 11 , wherein said at least one inductor L is added in parallel, and said corner frequency and said further corner frequency further depends on said at least one inductor L.
13. The receiver of claim 4 , wherein said receiver is a part of a mobile terminal, a mobile phone, a handset device or a mobile communication device.
14. The receiver of claim 4 , wherein an integrated circuit comprises all or selected components of said receiver.
15. A communication device, comprising:
a receiver, configured to perform transferred-impedance filtering, said receiver comprises:
an amplifier containing a resistance R on its output and, configured to amplify a radio frequency signal and to generate, an amplified radio frequency signal; and
at least one transferred-impedance filter, configured to filter said amplified radio frequency signal, said transferred-impedance filter containing at least one capacitor and having a pass band with a center frequency determined by a reference frequency, wherein −3dB frequencies of said pass band are given by said reference frequency plus a corner frequency which depends on said resistance R and a capacitance C of said at least one capacitor and by said reference frequency minus a further corner frequency which also depends on said resistance R and said capacitance C.
16. The communication device of claim 15 , wherein the receiver further comprises:
an attenuator, configured to attenuate by a predefined value the amplified radio frequency signal in a separate channel from said transferred-impedance filter for generating an attenuated amplified radio frequency signal; and
a mixer, configured to generate a subtraction signal between the filtered amplified radio frequency signal and said attenuated amplified radio frequency signal.
17. A transferred-impedance filter coupled to an amplifier having a resistance R, said transferred-impedance filter comprising:
at least one capacitor, said one transferred-impedance filter being configured to filter a radio frequency signal from said amplifier and to generate a filtered radio frequency signal, and further configured to have a pass band with a center frequency determined by a reference frequency, wherein −3 dB frequencies of said pass band are given by said reference frequency plus a corner frequency which depends on said resistance R and a capacitance C of said at least one capacitor and by said reference frequency minus a further corner frequency which also depends on said resistance R and said capacitance C.
18. The transferred-impedance filter of claim 17 , wherein said corner frequency and said further corner frequency are equal and given by F RC =1/π2RC.
19. The transferred-impedance filter of claim 17 , wherein said reference frequency is a local oscillator frequency F LO provided to said transferred-impedance filter.
20. The transferred-impedance filter of claim 17 , wherein said transferred-impedance filter is configured to perform a down conversion mixing function such that a low frequency baseband signal is an output signal of said transferred-impedance filter.
21. The transferred-impedance filter of claim 17 , further comprising:
at least one inductor L added in series with said at least one capacitor C and said reference frequency is given by F LO -F LC or F LO +F LC , said F LO being a local oscillator frequency provided to said transferred-impedance filter and said F LC being an LC resonant frequency given by F LC =1/2π√{square root over (LC)}.
22. The transferred-impedance filter of claim 17 , further comprising:
at least one inductor L is added in parallel with said at least one capacitor C and said reference frequency is given by F LO -F LC or F LO =F LC , said F LO being a local oscillator frequency provided to said transferred-impedance filter and said F LC being an LC resonant frequency given by F LC =1/2π√{square root over (LC)}.
23. The transferred-impedance filter of claim 22 , wherein said corner frequency and said further corner frequency further depends on said at least one inductor L.
24. The transferred-impedance filter of claim 17 , wherein said transferred-impedance filter is a part of a receiver, a mobile terminal, mobile phone, a handset device or a mobile communication device.
25. The transferred-impedance filter of claim 17 , wherein an integrated circuit comprises all or selected components of said transferred-impedance filter