Multiple band RF transmitters and receivers having independently variable RF and IF local oscillators and independent high-side and low-side RF local oscillators
Multistage RF transmitter and receiver circuits may use independently variable RF and IF local oscillators, allowing the RF and IF local oscillator frequencies for a given RF channel to be selected to have a large common factor with respect to the reference oscillator used by the local oscillator circuits, thus allowing the use of small divisor numbers in the local oscillator circuits and reducing phase noise. Independent high-side and low-side RF local oscillators may be provided and selectively used depending on the RF channel to be transmitted or received.
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1. Field of the Invention
Embodiments of the invention related to radio frequency (RF) transceivers, and particularly to transceiver architectures employing multiple stages for modulation or demodulation of signals.
2. Related Technology
Transceiver circuits are used in devices that receive or transmit information using radio frequency modulation. Examples of devices that use transceiver circuits include wireless LAN interfaces, cell phones, personal digital assistants, GPS receivers and other devices having RF communication features.
Transceiver circuit architectures may be categorized by the manner in which they modulate and demodulate signals.
The transmitter and receiver architectures of
The direct conversion method is sometimes preferred for its relatively simple architecture, however it also has a number of drawbacks. For example, in order to provide high accuracy in the mixers, it is necessary for the mixers to receive differential inputs. This requires the use of a balun, which in turn requires the use of multiple inductors that increase the total size of the circuit. Also, because there are few amplifier stages, this architecture also requires the use of very low noise amplifiers, which necessitates large amplifier size and power consumption.
Other drawbacks of direct conversion architectures are specific to the local oscillator circuit. In the direct conversion architecture, the local oscillator circuit must produce exact frequencies for down-converting or up-converting to the particular channels. For example, in wireless LAN devices, a direct conversion local oscillator for the 802.11b/g standards must produce frequencies that are adjustable in increments of 5 MHz from 2412 MHz to 2477 MHz, and also 2484 MHz. For the 802.11j standard, the local oscillator must produce frequencies that are adjustable in increments of 20 MHz from 4920 MHz to 4980 MHz, from 5040 MHz to 5080 MHz, and from 5170 MHz to 5230 MHz. For the 802.11a standard, the local oscillator must produce frequencies that are adjustable in increments of 20 MHz from 5180 MHz to 5320 MHz, and from 5745 MHz to 5845 MHz. The need for a local oscillator that is adjustable in this manner is a significant restraint on device performance because it requires the use of a local oscillator that generates significant phase noise.
In addition to high phase noise, the high frequency local oscillators used in direct conversion architectures typically suffer from high flicker noise, significant skew between in-phase and quadrature signals, and significant DC offsets between the differential baseband signals. The need to produce in-phase and quadrature signals at higher frequencies also requires these local oscillators to utilize on-chip inductors that consume significant area.
An alternative to direct conversion transceiver architectures is the multistage or superheterodyne transceiver architecture.
During operation, the superheterodyne receiver down-converts the received RF signal to a fixed intermediate frequency and then performs a second down-conversion of the intermediate frequency to baseband. For purposes of channel selection, the RF local oscillator frequency is varied so as to down-convert the frequency of the selected channel to the fixed intermediate frequency, and spurious tones from adjacent channels are removed by the SAW filter 76.
One alternative version of the superheterodyne architecture is sometimes referred to as a “sliding IF” architecture. The sliding IF architecture differs from the architecture of
The superheterodyne transceiver architecture has several advantages over the direct conversion architecture. High gain in the front end amplifier 70 and in the RF mixer 72 relaxes the noise requirements for the baseband amplifiers 88, 90 and therefore reduces the size and power requirements of the baseband amplifiers. Also, second order distortion in this circuit is less crucial and so a single ended amplifier topology may be used at the front end, resulting in a lower noise figure for the circuit as a whole. With regard to the local oscillators, the ability to use a single ended topology in the first down-conversion stage eliminates the need for the inductors required by the direct conversion mixer as well as the inductors required for a front-end balun. Also, the generation of in-phase and quadrature signals is much more accurate at intermediate frequencies than at direct conversion frequencies, and so the intermediate frequency local oscillator produces more accurate signals and results in lower DC offsets in the baseband signals.
Despite these advantages, the superheterodyne transceiver architecture also has several drawbacks. The need for a SAW filter 76 between the RF and IF mixing stages is a disadvantage because SAW filters are discrete components that are expensive and relatively large. Further, in order to reduce the introduction of noise from image channels, the RF mixer must be implemented as an image reject mixer, which consumes a relatively large amount of space and power. In addition, the need to down-convert the various channels within the RF band to a fixed intermediate frequency requires the RF local oscillator to be adjustable among values dictated by the channel frequencies and the intermediate frequency, leading to phase noise problems similar to those described in regard to direct conversion architectures.
One alternative to the superheterodyne architecture of
Therefore both the direct conversion and superheterodyne architectures have shortcomings that limit device performance, size and expense.
SUMMARYEmbodiments of the invention may use independently variable RF and IF local oscillators in multistage receiver and transmitter circuits. The RF and IF local oscillator frequencies for a given RF channel may therefore be selected to have a large common factor with respect to the reference oscillator used by the local oscillator circuits, thus allowing the use of small divisor numbers in the local oscillator circuits and reducing phase noise.
Other embodiments of the invention include both high-side and low-side RF local oscillators, and selectively use a high-side or low-side local oscillator frequency depending on the RF channel to be transmitted or received. Each of the RF local oscillators has a relatively small duty ranges which enhances performance. The local oscillator signal ranges are also prevented from overlapping the RF band to be transmitted and received, which reduces oscillator signal leakage. This also allows the image bands to be located at significant distances from the RF band to be transmitted and received. As a result, the image rejection and filtering constraints of the circuits are relaxed, allowing the use of smaller, less expensive and less complex mixing and filtering elements.
DESCRIPTION OF THE DRAWINGS
The receiver and transmitter circuits of
The receiver and transmitter circuits of
The receiver and transmitter circuits of
The receiver and transmitter circuits of
The receiver and transmitter circuits of
Both the RF mixers 110,112 and the IF mixers 116, 118 of the receiver circuit of
As discussed below with respect to
The frequencies produced by the RF local oscillators and the IF local oscillator are controlled by a local oscillator frequency control logic circuit 136. Connections between the control logic circuit 136 and the local oscillators are represented in
Referring now to
The local oscillator signals received by the RF mixers 148,150 and the IF mixers 144, 146 have variable frequencies local oscillator signals. The IF mixers 144, 146 receive variable in-phase and quadrature signals from a variable IF local oscillator 156. The RF mixer 148 for the 802.11a/j band receives a variable local oscillator signal from a low-side RF local oscillator 158 or from a high-side RF local oscillator 160. The RF mixer for the 802.11b/g band receives a variable local oscillator signal from a high-side RF local oscillator 162.
The frequencies produced by the RF local oscillators and the IF local oscillator are controlled by a local oscillator frequency control logic circuit 164. Connections between the control logic circuit 164 and the local oscillators are represented in
As discussed below with respect to
Further, although illustrated separately in
Reference is now made to
The frequency plan of
For the upper 802.11a band, a high-side local oscillator in the range of 6520-6560 MHz is used, resulting in an image band in the range of 7285-7345 MHz. Signals in this image band are easily attenuated and therefore this image band does not tighten the rejection and filtering requirements of the receiver circuit.
Reference is now made to
Examining
The first frequency synthesizer 200 is comprised of a frequency divider 208 that receives the reference frequency and outputs a divided frequency to a phase frequency detector 210. A charge pump 212 receives a control signal from the phase frequency detector 210 and drives current into and out of a low pass filters 214. The charge in the low pass filters 214 serves as a control signal for separate voltage controlled oscillators 216 and 218 which are both biased by a commonly shared bias circuit 220. The first voltage controlled oscillator 216 produces a low-side RF local oscillator frequency for the lower 802.11a/j band. The output of this oscillator 216 is provided directly to a frequency divider 222 that supplies a signal to the phase frequency detector 210 to complete the phase locked loop for the 802.11a/j low-side RF local oscillator. The second voltage controlled oscillator 218 produces a high-side RF local oscillator frequency for the upper 802.11a band. The output of this oscillator 218 is supplied to a frequency divider 202 where the frequency is divided by two. [please explain again why it is necessary to divide by two before going to the frequency divider of the phase locked loop] The output of this frequency divider 202 is then supplied to the main frequency divider 222, which supplies a signal to the phase frequency detector 210 to complete the phase locked loop for the 802.11a/j high-side RF local oscillator. As noted above, the output of the frequency divider 202 also provides a high-side RF local oscillator signal for the 802.11b/g band.
The second frequency synthesizer 204 is comprised of a frequency divider 224 that receives the reference frequency and outputs a divided frequency to a phase frequency detector 226. A charge pump 228 receives a control signal from the phase frequency detector 226 and drives current into and out of a low pass filter 230. The charge in the low pass filter 230 serves as a control signal for a voltage controlled oscillator 232 that is biased by a bias circuit 234. The output of the voltage controlled oscillator 232 is provided to a frequency divider 236 that supplies a signal to the phase frequency detector 226 to complete the phase locked loop for the IF local oscillator. The output of the voltage controlled oscillator 232 is also provided to a frequency divider 238 that divides the output frequency of the voltage controlled oscillator 232 by four to produce differential in-phase and quadrature signals having a frequency that is one quarter of the frequency of the voltage controlled oscillator 232.
The local oscillator signals produced by the circuit of
During operation, the RF local oscillator frequencies and IF local oscillator frequencies produced by the circuit of
The aforementioned divisor numbers and element states are controlled by a local oscillator frequency control logic circuit 248 in response to a control signal that indicates the RF channel to be used by the receiver and transmitter. Examples of divisor numbers and corresponding VCO and local oscillator frequencies for the circuit of
The Tables of
The local oscillator configuration table 250 of the circuit of
The local oscillator configuration table may be stored in a non-volatile memory unit or may be loaded into a memory element upon initialization of system control software that controls the transceiver circuit and other components in a device in which the transceiver circuit is implemented, such as a wireless LAN interface device.
While one embodiment of the invention uses a local oscillator configuration table as described above, other embodiments of the invention may eliminate the configuration table and simply supply configuration data bits directly to the local oscillator control logic circuit as a control signal representing frequency synthesizer divisor values and element states.
The circuits described herein provide a number of advantages over conventional direct conversion and superheterodyne architectures.
The circuits, devices, processes and features described herein are not exclusive of other circuits, devices, processes and features, and variations and additions may be implemented in accordance with the particular objectives to be achieved. For example, circuits as described herein may be integrated with other circuits not described herein to provide further combinations of features, to operate concurrently within the same devices, or to serve other purposes. Thus it should be understood that the embodiments illustrated in the figures and described above are offered by way of example only. The invention is not limited to a particular embodiment, but extends to various modifications, combinations, and permutations that fall within the scope of the claims and their equivalents.
Claims
1. A receiver circuit for down-converting a radio frequency (RF) signal, comprising:
- an RF mixer that down-converts an RF signal to an intermediate frequency (IF) signal;
- a first variable frequency RF local oscillator that supplies a first RF local oscillator frequency to the RF mixer;
- an IF mixer that down-converts the IF signal to a baseband signal; and
- a variable frequency IF local oscillator that supplies an IF local oscillator frequency to the IF mixer, the IF local oscillator frequency being variable independently of variations of the first RF local oscillator frequency.
2. The circuit claimed in claim 1, further comprising a local oscillator control circuit that sets the first RF local oscillator frequency and the IF local oscillator frequency in accordance with an RF channel to be down-converted.
3. The circuit claimed in claim 2, further comprising a local oscillator configuration table referenced by the local oscillator control circuit to set the first RF local oscillator frequency and IF local oscillator frequency, the configuration table storing data indicating RF local oscillator configurations and IF local oscillator configurations corresponding to respective RF channels.
4.-7. (canceled)
8. An integrated circuit chip embodying the receiver circuit of claim 1.
9. An RF communication device embodying the receiver circuit of claim 1.
10. A transmitter circuit for producing a radio frequency (RF) signal, comprising:
- an IF mixer that up-converts a baseband signal to an intermediate frequency (IF) signal;
- a variable frequency IF local oscillator that supplies an IF local oscillator frequency to the IF mixer;
- an RF mixer that up-converts the intermediate frequency (IF) signal to an RF signal; and
- a first variable frequency RF local oscillator that supplies a first RF local oscillator frequency to the RF mixer,
- the IF local oscillator frequency being variable independently of variations of the first RF local oscillator frequency.
11. The circuit claimed in claim 10, further comprising a local oscillator control circuit that sets the first RF local oscillator frequency and the IF local oscillator frequency in accordance with an RF channel to be transmitted.
12. The circuit claimed in claim 11, further comprising a local oscillator configuration table referenced by the local oscillator control circuit to set the first RF local oscillator frequency and IF local oscillator frequency, the configuration table storing data indicating RF local oscillator configurations and IF local oscillator configurations corresponding to respective RF channels.
13.-16. (canceled)
17. An integrated circuit chip embodying the transmitter circuit of claim 10.
18. An RF communication device embodying the transmitter circuit of claim 10.
19. A transceiver circuit for radio frequency (RF) communications, comprising:
- an RF receiver mixer that down-converts an RF received signal to an intermediate frequency (IF) received signal;
- an IF receiver mixer that down-converts the IF received signal to a baseband received signal;
- an IF transmit mixer that up-converts a baseband transmit signal to an IF transmit signal;
- an RF transmit mixer that up-converts the IF transmit signal to an RF transmit signal;
- a first variable frequency RF local oscillator that supplies a first RF local oscillator frequency to the RF receiver mixer and the RF transmit mixer; and
- a variable frequency IF local oscillator that supplies an IF local oscillator frequency to the IF receiver mixer and the IF transmit mixer, the IF local oscillator frequency being variable independently of variations of the first RF local oscillator frequency.
20. The circuit claimed in claim 19, further comprising a local oscillator control circuit that sets the first RF local oscillator frequency and the IF local oscillator frequency in accordance with an RF channel to be transmitted and received.
21. The circuit claimed in claim 20, further comprising a local oscillator configuration table referenced by the local oscillator control circuit to set the first RF local oscillator frequency and IF local oscillator frequency, the configuration table storing data indicating RF local oscillator configurations and IF local oscillator configurations corresponding to respective RF channels.
22.-25. (canceled)
26. An integrated circuit chip embodying the transceiver circuit of claim 19.
27. An RF communication device embodying the transceiver circuit of claim 19.
28. A radio frequency (RF) receiver circuit comprising:
- an RF mixer that down-converts a received RF signal;
- a first variable frequency RF local oscillator that supplies a first RF local oscillator frequency;
- a second variable frequency RF local oscillator that supplies a second RF local oscillator frequency; and
- a local oscillator control circuit that selectively controls the first variable frequency RF local oscillator and the second variable frequency RF local oscillator to supply a low-side local oscillator signal from the first variable frequency RF local oscillator to the RF mixer or a high-side local oscillator signal from the second variable frequency RF local oscillator to the RF mixer in accordance with an RF channel to be down-converted.
29. The circuit claimed in claim 28, wherein the local oscillator control circuit controls the first variable frequency RF local oscillator and the second variable frequency RF local oscillator to supply a low-side local oscillator signal for down-converting channels of the 802.11a standard in the range of 5.18 GHz to 5.32 GHz and to supply a high-side local oscillator signal for down-converting channels of the 802.11 a standard in the range of 5.745 GHz to 5.805 GHz.
30. The circuit claimed in claim 28, further comprising a local oscillator configuration table referenced by the local oscillator control circuit to control the first variable frequency RF local oscillator and the second variable frequency RF local oscillator, the configuration table storing data indicating RF local oscillator configurations corresponding to respective RF channels.
31. The circuit claimed in claim 28, wherein the first variable frequency RF local oscillator and the second variable frequency RF local oscillator are implemented as a phase locked loop comprising a first voltage controlled oscillator producing the first RF local oscillator frequency and a second voltage controlled oscillator producing the second RF local oscillator frequency.
32. The circuit claimed in claim 28, wherein the RF mixer converts the RF signal to an intermediate frequency (IF) signal,
- wherein the receiver circuit further comprises: an IF mixer that down-converts the IF signal to a baseband signal; and a variable frequency IF local oscillator that supplies an IF local oscillator frequency to the IF mixer, the IF local oscillator frequency being variable independently of variations of the first RF local oscillator frequency and the second RF local oscillator frequency, and
- wherein the local oscillator control circuit sets the IF local oscillator frequency of the variable frequency IF local oscillator in accordance with an RF channel to be down-converted.
33. An integrated circuit chip embodying the receiver circuit of claim 28.
34. An RF communication device embodying the receiver circuit of claim 28.
35. A radio frequency (RF) transmitter circuit comprising:
- an RF mixer that up-converts a signal to an RF frequency;
- a first variable frequency RF local oscillator that supplies a first RF local oscillator frequency;
- a second variable frequency RF local oscillator that supplies a second RF local oscillator frequency; and
- a local oscillator control circuit that selectively controls the first variable frequency RF local oscillator and the second variable frequency RF local oscillator to supply a low-side local oscillator signal from the first variable frequency RF local oscillator to the RF mixer or a high-side local oscillator signal from the second variable frequency RF local oscillator to the RF mixer in accordance with an RF channel to be transmitted.
36. The circuit claimed in claim 35, wherein the local oscillator control circuit controls the first variable frequency RF local oscillator and the second variable frequency RF local oscillator to supply a low-side local oscillator signal for up-converting to channels of the 802.11a standard in the range of 5.18 GHz to 5.32 GHz and to supply a high-side local oscillator signal for up-converting to channels of the 802.11a standard in the range of 5.745 GHz to 5.805 GHz.
37. The circuit claimed in claim 35, further comprising a local oscillator configuration table referenced by the local oscillator control circuit to control the first variable frequency RF local oscillator and the second variable frequency RF local oscillator, the configuration table storing data indicating RF local oscillator configurations corresponding to respective RF channels.
38. The circuit claimed in claim 35, wherein the first variable frequency RF local oscillator and the second variable frequency RF local oscillator are implemented as a phase locked loop comprising a first voltage controlled oscillator producing the first RF local oscillator frequency and a second voltage controlled oscillator producing the second RF local oscillator frequency.
39. The circuit claimed in claim 35, wherein the RF mixer up-converts an intermediate frequency (IF) signal to an RF signal,
- wherein the transmitter circuit further comprises: an IF mixer that up-converts a baseband signal to the IF signal; and a variable frequency IF local oscillator that supplies an IF local oscillator frequency to the IF mixer, the IF local oscillator frequency being variable independently of variations of the first RF local oscillator frequency and the second RF local oscillator frequency, and
- wherein the local oscillator control circuit sets the IF local oscillator frequency of the variable frequency IF local oscillator in accordance with an RF channel to be transmitted.
40. An integrated circuit chip embodying the transmitter circuit of claim 35.
41. An RF communication device embodying the transmitter circuit of claim 35.
42. A radio frequency (RF) transceiver circuit comprising:
- an RF receiver mixer that down-converts a received RF signal;
- an RF transmit mixer that up-converts a transmit signal to an RF transmit signal;
- a first variable frequency RF local oscillator that supplies a first RF local oscillator frequency;
- a second variable frequency RF local oscillator that supplies a second RF local oscillator frequency; and
- a local oscillator control circuit that selectively controls the first variable frequency RF local oscillator and the second variable frequency RF local oscillator to supply a low-side local oscillator signal from the first variable frequency RF local oscillator to the RF receiver mixer and the RF transmit mixer or a high-side local oscillator signal from the second variable frequency RF local oscillator to the RF receiver mixer and the RF transmit mixer in accordance with an RF channel to be received and transmitted.
43. The circuit claimed in claim 42, wherein the local oscillator control circuit controls the first variable frequency RF local oscillator and the second variable frequency RF local oscillator to supply a low-side local oscillator signal for receiving and transmitting channels of the 802.11a standard in the range of 5.18 GHz to 5.32 GHz and to supply a high-side local oscillator signal for receiving and transmitting channels of the 802.11a standard in the range of 5.745 GHz to 5.805 GHz.
44. The circuit claimed in claim 42, further comprising a local oscillator configuration table referenced by the local oscillator control circuit to control the first variable frequency RF local oscillator and the second variable frequency RF local oscillator, the configuration table storing data indicating RF local oscillator configurations corresponding to respective RF channels.
45. The circuit claimed in claim 42, wherein the first variable frequency RF local oscillator and the second variable frequency RF local oscillator are implemented as a phase locked loop comprising a first voltage controlled oscillator producing the first RF local oscillator signal frequency and a second voltage controlled oscillator producing the second RF local oscillator frequency.
46. The circuit claimed in claim 42, wherein the RF receiver mixer down-converts an RF received signal to an intermediate frequency (IF) received signal,
- wherein the RF transmit mixer up-converts an intermediate frequency (IF) signal to the RF transmit signal,
- wherein the transceiver circuit further comprises: an IF receiver mixer that down-converts the IF received signal to a baseband received signal; an IF transmit mixer that up-converts a baseband transmit signal to the IF transmit signal; and a variable frequency IF local oscillator that supplies an IF local oscillator frequency to the IF receiver mixer and the IF transmit mixer, the IF local oscillator frequency being variable independently of variations of the first RF local oscillator frequency and the second RF local oscillator frequency, and
- wherein the local oscillator control circuit sets the IF local oscillator frequency of the variable frequency IF local oscillator in accordance with an RF channel to be received and transmitted.
47. An integrated circuit chip embodying the transceiver circuit of claim 42.
48. An RF communication device embodying the transceiver circuit of claim 42.
49. A method of operating a radio frequency (RF) transceiver circuit, comprising:
- receiving a signal indicating an RF channel to transmit or receive;
- obtaining RF local oscillator configuration data and intermediate frequency (IF) local oscillator configuration data for the RF channel from a table containing local oscillator configuration data for respective RF channels;
- setting an RF local oscillator to produce an RF local oscillator frequency in accordance with said obtained RF local oscillator configuration data; and
- setting an IF local oscillator to produce an IF local oscillator frequency in accordance with said obtained IF local oscillator configuration data.
50. A method of operating a radio frequency (RF) transceiver circuit, comprising:
- receiving a signal indicating an RF channel to transmit or receive; and
- selectively providing one of a high-side RF local oscillator signal and a low-side RF local oscillator signal to an RF mixer in accordance with the RF channel to up-convert or down-convert the RF channel.
Type: Application
Filed: May 16, 2007
Publication Date: Sep 20, 2007
Applicant:
Inventors: Zaw Soe (Encinitas, CA), Tony Yang (Whitford, CA), Jackie Cheng (Irvine, CA), Sining Zhou (Irvine, CA), Kuangyu Li (Glendale, CA), Fei-Ran Yang (Diamond Bar, CA), Shoufang Chen (Irvine, CA), Tom Baker (Los Angeles, CA)
Application Number: 11/804,516
International Classification: H04B 1/16 (20060101);