BRIEF DESCRIPTION OF THE DRAWINGS
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
FIG. 1 is a block diagram of an embodiment of a conventional radio frequency signal receiver with intermediate frequency automatic gain control (IFAGC).
FIG. 2 is a block diagram of another embodiment of a conventional radio frequency signal receiver with radio frequency automatic gain control (RFAGC).
FIG. 3 is a spectrum diagram of signals after processing by LNA, mixer and channel selection filter in FIG. 2.
FIG. 4 is a block diagram of an embodiment of the radio frequency receiver with radio frequency automatic gain control (RFAGC) according to the invention.
FIG. 5 is a spectrum diagram of signals after processing by LNA, mixer and channel selection filter in FIG. 4.
FIG. 6 is a block diagram of yet another embodiment of the radio frequency receiver with radio frequency automatic gain control (RFAGC) according to the invention.
FIG. 7 is a block diagram of another embodiment of the radio frequency receiver with radio frequency automatic gain control (RFAGC) according to the invention.
FIG. 8 is a signal spectrum diagram showing the output signal when the AGC unit is enabled and is disabled.
DETAILED DESCRIPTION OF THE INVENTION
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
FIG. 4 is a block diagram of an embodiment of the radio frequency receiver according to the invention. A low noise amplifier (LNA) 41 receives and amplifies radio frequency (RF) signals. The mixer 43 down converts the amplified RF signals to in-phase (I) signals and quadrature-phase (Q) signals based on the output signal of the local oscillator (LO) 42. The channel selection filter 44 receives and filters the signals I and Q to develop the desired channel signals. The limiting amplifier 45 receives and amplifies the output signals from the channel selection filter 44. The automatic gain control (AGC) unit 46 adjusts the gain of the LNA 41, mixer 43 and channel selection filter 44 based on the output signals of LNA 41. According to the architecture of the receiver shown in FIG. 4, the present invention provides adequate gain control for a radio frequency receiver to increase its dynamic range, which reduces non-linear spurs generated after the channel selection filter 44.
Please refer to FIG. 5 for further illustration. FIG. 5 is a spectrum diagram signals processed by LNA, mixer, channel selection filter, and AGC unit in FIG. 4. In S1, the strength of Signal is −50 dBm, and the strength of Adj. is −30 dBm. In S2, i.e. signals Signal and Adj. has been processed by LNA 41 and mixer 43, the strength of Signal and Adj. respectively increases to −20 dBm and 0 dBm. In the following, signals Signal and Adj. are processed by the channel selection filter 44 with an adaptive gain from 10 dB to 0 dB, which possess wider dynamic range of the channel selection filter 44 about 10 dB compared with the channel selection filter 14. Therefore, the AGC unit 46 is able to adjust the gain of the channel selection filter 44 to prevent from generating strong non-linear spurs. Comparing S3 of FIG. 5 and the S3 in FIG. 3, the non-linear spurs are negligible due to the adequate dynamic range of channel selection filter 44.
FIG. 6 is a block diagram of yet another embodiment of the radio frequency receiver according to the invention. A low noise amplifier (LNA) 41 receives and amplifies radio frequency (RF) signals. The mixer 43 down converts the amplified RF signals to in-phase (I) signals and quadrature-phase (Q) signals based on the output signal of the local oscillator (LO) 42. The channel selection filter 44 receives and filters the signals I and Q to develop the desired channel signals. The limiting amplifier 45 receives and amplifies the output signals from the channel selection filter 44. A gain stage unit 47, which could be an operation amplifier, amplifies the signals I and Q based on the gain control from the channel selection filter 44. The channel selection filter 44 receives and filters the signals to output the desired channel signals. The automatic gain control (AGC) unit 46 adjusts the gain of the LNA 41, mixer 43 and gain stage unit 47 based on the output signals of LNA 41. According to the architecture of the receiver shown in FIG. 6, the present invention provides adequate gain control for a radio frequency receiver to increase its dynamic range, which reduces non-linear spurs generated after the channel selection filter 44.
FIG. 7 is a block diagram of yet another embodiment of the radio frequency receiver according to the invention. The low noise amplifier (LNA) 41 receives and amplifies radio frequency (RF) signals. The mixer 43 down converts the amplified RF signals to in-phase (I) signals and quadrature-phase (Q) signals based on the output signal of the local oscillator (LO) 42. The channel selection filter 44 receives and filters the signals I and Q to develop the desired channel signals. The limiting amplifier 45 receives and amplifies the output signals from the channel selection filter 44. The received signal strength indicator (RSSI) module 48 generates a RSSI value according to the amplified output signal from the limiting amplifier 45, and further outputs a turn-on signal according to the RSSI value to activate the AGC unit 46 when the strength of the output signal exceeds a first predetermined strength, and a turn-off signal to disable the AGC unit 46 when the strength of the output signal is below a second predetermined strength. In this embodiment, the present architecture can avoid continuous switching on/off at the AGC unit 46. The turn-on and turn-off signals can be generated by any hardware and/or software control method implemented in the RSSI module 48. When the AGC unit 46 turns on in response to the received turn-on signal, the AGC unit 46 adjusts the gain of the LNA 41, mixer 43 and channel selection filter 44 based on the output signals of LNA 41. According to the architecture of the receiver shown in FIG. 7, the present invention provides adequate gain control for a radio frequency receiver to increase its dynamic range, which reduces non-linear spurs generated after the channel selection filter 44.
FIG. 8 is a signal spectrum diagram showing the output spectrum when the AGC unit is enabled (AGC-on) and disabled (AGC-off). When the AGC unit 46 of the present invention is disabled, the non-linear spurs caused by the adjacent channel interference will reduce the quality of the desired channel signal. When the AGC unit 46 of the present invention is enabled, the strength of the non-linear spurs and the adjacent channel interference decrease significantly, so the quality of the desired channel signal and the performance of the receiver will be improved.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Patent Application
20070293177
