Method and apparatus for conversion of radio frequency (RF) signals using aperiodic mixing signals
An inexpensive, high-performance, fully-integrable, multi-standard transceiver with a topology including: an active mixer, followed by a high pass filter, and a passive mixer. The input signal is modulated up, or demodulated down, using a pair of complementary, aperiodic mixing signals. The use of aperiodic mixing signals allows a fully-integrated transceiver to be built. Embodiments of the active mixer include those having electrically-adjustable performance and allowing multiple RF signal inputs. This allows the topology to be employed in multi-band, multi-frequency applications, while still providing high performance.
1. A modulation or demodulation circuit comprising:
a synthesizer for generating a first aperiodic mixing signal φ 1 and second aperiodic mixing signals φ 2 , where φ 1 * φ 2 has significant power at the frequency of a local oscillator signal being emulated, and neither said first aperiodic mixing signal φ 1 nor said second aperiodic mixing signal φ 2 has significant power at the frequency of said local oscillator signal being emulated;
an active mixer for receiving an input signal and mixing said input signal with a first aperiodic mixing signal φ 1 , said active mixer having adjustable performance;
a high pass filter electrically connected to the output of said active mixer, generating a filtered, mixed signal; and
a passive mixer connected to the output of said high pass filter, for receiving said filtered, mixed signal and said second aperiodic mixing signal φ 2 , said second aperiodic mixing signal φ 2 being different from said first aperiodic mixing signal, and mixing said filtered, mixed signal with said second aperiodic mixing signal φ 2 , to generate a modulated or demodulated signal.
2. The circuit of claim 1 , wherein said first aperiodic mixing signal φ 1 and said second aperiodic mixing signal φ 2 emulate a local oscillator signal.
3. The circuit of claim 1 , further comprising a signal generator for generating said first aperiodic mixing signal φ 1 and said second aperiodic mixing signals φ 2 .
4. The circuit of claim 1 , wherein said active mixer has adjustable gain.
5. The circuit of claim 1 , wherein said active mixer has adjustable linearity.
6. The circuit of claim 1 , wherein said active mixer comprises a current source whose parameters can be adjusted to control gain and linearity of said active mixer.
7. The circuit of claim 1 , wherein said active mixer comprises multiple driver components, each for receiving a different input signal in a multi-standard radio.
8. The circuit of claim 1 , wherein each of said active mixer, said filter and said passive mixer is a differential device.
9. The circuit of claim 1 , wherein the corner frequency of said high pass filter is low relative to the input and mixing signals, whereby it only suppresses DC signal components.
10. The circuit of claim 1 , wherein the corner frequency of said high pass filter is low relative to the input and mixing signals, whereby it only suppresses second order distortion.
11. The circuit of claim 1 , wherein said high pass filter comprises a resistor dividing network.
12. The circuit of claim 11 wherein said resistor dividing network comprises an active resistor dividing network.
13. The circuit of claim 11 wherein said resistor dividing network is calibrated to adjust the common mode voltage output.
14. The circuit of claim 4 , wherein said active mixer includes switches allowing its gain and noise figure to be adjusted, and said second mixer is purely passive thereby reducing its 1/f noise.
15. The circuit of claim 5 , wherein said active mixer includes switches allowing its noise figure and linearity to be adjusted.
16. The circuit of claim 1 , wherein said high pass filter comprises a capacitor in-line with the signal path.
17. The circuit of claim 1 wherein said active mixer comprises:
an RF amplifier for amplifying said input signal;
a balanced mixer for mixing said amplified input signal with said first aperiodic mixing signal φ 1 ; and
a current injection circuit arranged to provide extra current to said balanced mixer, thereby controlling the current supplied to said RF amplifier and reducing the current supplied through said balanced mixer.
18. The circuit of claim 17 wherein said active mixer comprises said RF amplifier and a pair of active balanced mixers in a totem pole arrangement.
19. The circuit of claim 17 wherein said RF amplifier comprises two transistors arranged to amplify a balanced RF input signal.
20. The circuit of claim 17 wherein said current injection circuit comprises a constant current source.
21. The circuit of claim 20 wherein said current injection circuit comprises multiple constant current sources thereby permitting variation in the gain of the RF amplifier and also permitting adjustment of the gain and linearity of the RF amplifier circuit during and after manufacture.
22. A method of up or down conversion comprising the steps of:
generating a first aperiodic mixing signal φ 1 and a second aperiodic mixing signals φ 2 , where φ 1 * φ 2 has significant power at the frequency of a local oscillator signal being emulated, and neither said first aperiodic mixing signal φ 1 nor said second aperiodic mixing signal φ 2 has significant power at the frequency of said local oscillator signal being emulated;
active mixing an input signal with a first aperiodic mixing signal φ 1 , to generate a first mixed signal;
high pass filtering said first mixed signal, to generate a filter signal; and
passive mixing said filter signal with a second aperiodic mixing signal, said second aperiodic mixing signal φ 2 being different from said first aperiodic mixing signal φ 1 , to generate a up or down converted signal.