The present invention will be further described in details in conjunction with the accompanying drawings.
Direct RF digitization is a proper scheme to down convert multiple signal bands at the same time. Direct RF digitization does not need plenty of analog components such as local oscillator (LO), mixer, etc. As mentioned, in direct RF digitization, an ADC (analog-to-digital converter) is used to sample RF signals with a sampling frequency so as to down convert the RF signals into IF (intermediate frequency) signals. Generally, the down-converted IF signals almost fall in basebands and will be actual baseband signals after IF wipe-off processing.
To simultaneously down convert signals of multiple bands with direct RF digitization, a shared ADC is used to sample RF signals of a plurality of bands with an optimal sampling frequency which is calculated for the bands. By using the optimal sampling frequency in the shared ADC, all input signal RF bands can be converted to IF bands simultaneously without overlapping each other.
Signals of the specific bands passing through the multiband pass filter 320 are digitized by a digitization unit, such as an ADC 330 so as to be down-converted into IF bands, which are near basebands. The details will be further described later. The digitized signals are registered in a storage device 340, which can be a memory or just a register. The digitized signals are then processed with IF wipe-off operation by an IF wipe-off unit 350 to remove the residual IF components therefrom. The signals output from the IF wipe-off unit 350 are actually the baseband signals. The baseband signals are passed to the rear stage of the receiver for post processing, such as correlation and demodulation, of which the descriptions are omitted.
The receiver in accordance with the present invention further has a programmable frequency provision unit 360. The programmable frequency provision unit 360 provides a proper sampling frequency fs to the ADC 330 for the specific band combination designated in the multiband pass filter 320. The ADC 330 digitized the signals with the sampling frequency fs to down-convert the signals of the specific bands into corresponding IF bands, respectively. For different modes of the multiband pass filter 320, band combinations are different. Generally, the required sampling frequency to be used in the shared ADC 330 is different for each mode. The programmable frequency provision unit 360 can be built with a look-up table. Optimal sampling frequencies for various band combinations are calculated in advance and stored in the look-up table. Accordingly, the programmable frequency provision unit 360 is able to provide a proper sampling frequency for the bands selected to use by picking up the sampling frequency of the specific band combination from the built-in look-up table. Alternatively, the programmable frequency provision unit 360 calculates the sampling frequency fs for the bands selected to pass through the multiband pass filter 320 and provides the calculated sampling frequency fs to the ADC 330. In this case, the programmable frequency provision unit 360 is preferably comprises a dedicated calculation logic circuit or a processor.
The programmable frequency provision unit 360 also provides IF frequencies to the IF wipe-off unit 350 so that the IF wipe-off unit 350 can remove the residual IF components from the signals to convert the signals into actual baseband (BB) signals. In the present embodiment, the IF wipe-off unit 350 is time multiplexing (i.e. time division multiplex; TDM) for different bands, and therefore only one IF wipe-off unit is needed. As described above, data stream from the ADC 330 is stored in the storage device 340 to wait for being processed by the TDM IF wipe-off unit 350. If a number of IF wipe-off units are used simultaneously for processing signals of the respective bands, the storage device 340 can be omitted.
The suitable sampling frequency for digitization and the IF frequencies for IF wipe-off are adjustable by the programmable frequency provision unit due to performance concern, such as a resultant SNR (signal-to-noise ratio).
The ADC 430 digitizes the RF signals to down convert them into IF signals. In the present embodiment, the band sieving unit is implemented by a tunable band pass filter 445. The IF signals are filtered by the tunable band pass filter 445 with tunable coefficients. The tunable band pass filter 445, which can be implemented by an FIR (finite impulse response) filter, only allows signals of selected bands to pass. The tunable band pass filter 445 can be designed as operating in TDM form. That is, the tunable band pass filter 445 allows signals of the respective bands to pass through in different periods of time. For example, assumed that the selected bands are GPS L1 and L2, in a first period, the tunable band pass filter 445 allows signals of L1 to pass, and in a second period, the tunable band pass filter 445 allows signals of L2 to pass.
The IF signals passing through the tunable band pass filter 445 are subjected to IF wipe-off operation by an IF wipe-off unit 450. As the first embodiment, the IF wipe-off unit 450 is time multiplexing (i.e. TDM) for different bands, and therefore only one IF wipe-off unit is needed.
The receiver of
Although the present invention is more advantageous to the direct RF digitization using a single shared ADC, the present invention can also applied to the direct RF digitization using a plurality of ADC's.
While the preferred embodiment of the present invention has been illustrated and described in details, various modifications and alterations can be made by persons skilled in this art. The embodiment of the present invention is therefore described in an illustrative but not in a restrictive sense. It is intended that the present invention should not be limited to the particular forms as illustrated, and that all modifications and alterations which maintain the spirit and realm of the present invention are within the scope as defined in the appended claims.