Transferred-impedance filtering in RF receivers
View Patent ↗The present invention provides a method 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 signal by an antenna of a receiver;
amplifying said electrical signal using an amplifier containing a resistance R, for generating an amplified RF signal; and
filtering said amplified RF signal in response to a reference signal comprising a reference frequency and using at least one transferred-impedance filter containing at least one capacitor C and having a pass band with a center frequency equal to said reference frequency, wherein −3 dB frequencies of said pass band are given by said reference frequency plus a corner frequency which depends on said resistor R and said at least one capacitor C and by said reference frequency minus a further corner frequency which also depends on said resistor R and said at least one capacitor C.
2. The method of claim 1 , wherein said corner frequency and said further corner frequency are equal and given by F RC =1/πRC.
3. The method of claim 2 , wherein said at least one transferred-impedance filter also performs a down conversion mixing function such that a low frequency baseband signal is an output signal of said transferred-impedance filter.
4. The method of claim 1 , wherein said reference frequency is a local oscillator frequency F LO provided to said transferred-impedance filter.
5. The method of claim 1 , wherein said filtering is performed using 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.
6. The method of claim 1 , 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.
7. The method of claim 1 , wherein at least one inductor L is 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 =½π√{square root over (LC)}.
8. The method of claim 1 , wherein 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 =½π√{square root over (LC)}.
9. The method of claim 8 , wherein said corner frequency and said further corner frequency further depend on said at least one inductor L.
10. The method of claim 1 , wherein said receiver is a part of a mobile terminal, mobile phone or a mobile communication device.
11. The method of claim 1 , wherein said receiver is a radio frequency receiver.
12. A receiver comprising:
an antenna, for receiving a radio frequency signal and converting it to an electrical signal;
an amplifier containing a resistance R, for amplifying said electrical signal, for generating an amplified RF signal; and
at least one transferred-impedance filter, for filtering said amplified RF signal in response to a reference signal comprising a reference frequency said, transferred-impedance filter containing at least one capacitor C and having a pass band with a center frequency equal to said reference frequency, wherein −3 dB frequencies of said pass band are given by said reference frequency plus a corner frequency which depends on said resistor R and said at least one capacitor C and by said reference frequency minus a further corner frequency which also depends on said resistor R and said at least one capacitor C.
13. The receiver of claim 12 , wherein said corner frequency and said further corner frequency are equal and given by F RC =1/π2RC.
14. The receiver of claim 13 , 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.
15. The receiver of claim 12 , wherein said reference frequency is a local oscillator frequency FLO provided to said transferred-impedance filter.
16. The method of claim 12 , wherein said at least one transferred-impedance filter also performs a down conversion mixing function such that a low frequency baseband signal is an output signal of said transferred-impedance filter.
17. The receiver of claim 12 , 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.
18. The receiver of claim 12 , wherein at least one inductor L is 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/π2LC.
19. The receiver of claim 12 , wherein 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 =1/2√{square root over (LC)}.
20. The receiver of claim 19 , wherein said corner frequency and said further corner frequency further depend on said at least one inductor L.
21. The receiver of claim 12 , wherein said receiver is a part of a mobile terminal, mobile phone or a mobile communication device.
22. The receiver of claim 12 , wherein said receiver is a radio frequency receiver.
23. A communication device, comprising:
a receiver, for transferred-impedance filtering, said receiver comprises:
an antenna, for receiving a radio frequency signal and converting it to an electrical signal;
an amplifier containing a resistance R, for amplifying said electrical signal, for generating an amplified RF signal; and
at least one transferred-impedance filter, for filtering said amplified RF signal in response to a reference signal comprising a reference frequency, said transferred-impedance filter containing at least one capacitor C and having a pass band with a center frequency equal to said reference frequency, wherein ba−3 dB frequencies of said pass band are given by said reference frequency plus a corner frequency which depends on said resistor R and said at least one capacitor C and by said reference frequency minus a further corner frequency which also depends on said resistor R and said at least one capacitor C.
24. The communication device of claim 23 , wherein said corner frequency and said further corner frequency are equal and given by F RC =1/π2RC.
25. A receiver, comprising:
means for receiving a radio frequency signal and converting it to an electrical signal;
amplifying means containing a resistance R, for amplifying said electrical signal, for generating an amplified RF signal; and
at least one filtering means, for filtering said amplified RF signal in response to a reference signal comprising a reference frequency, said at least on filtering means containing at least one capacitor C and having a pass band with a center frequency equal to said reference frequency, wherein −3 dB frequencies of said pass band are given by said reference frequency plus a corner frequency which depends on said resistor R and said at least one capacitor C and by said reference frequency minus a further corner frequency which also depends on said resistor R and said at least one capacitor C.
26. The receiver of claim 25 , wherein said means for receiving is an antenna and said at least one filtering means is at least one transferred-impedance filter.