| 摘要 |
An Interleaved Radio Frequency Digital-to-Analog Converter (RF DAC) suitable for use in cellular base stations and optimized to give both a wide RF tuning range and a wide RF bandwidth is disclosed. The RF DAC uses two levels of interleaving, the first providing a direct conversion path from Base Band (BB) to RF, and the second providing a variable interleaving factor through the use of summation to optimize the output bandwidth as a function of the RF center frequency. Digital Interpolation, including an arbitrary sample rate conversion filter, allows the RF DAC to operate from a wide range of possible BB sample rates and the DAC sample rate is a fixed ratio of the RF center frequency. As a result, the spurious outputs from the RF DAC are in known locations that are relatively easy to filter out, minimizing the frequency planning tasks required for a complete RF system design. |
| 主权项 |
1. A radio frequency digital-to-analog converter (DAC) system comprising:
a first DAC to receive a first sample stream and to generate a first DAC output, the first sample stream being representable as first sub-streams that are interleaved with each other, the first DAC comprising a plurality of first Sub-DACs, each first Sub-DAC of the plurality of first Sub-DACs sampling a respective first sub-stream as a function of a respective clock signal, each first Sub-DAC generating a respective first Sub-DAC output, the first DAC further comprising a first summation device to receive and sum together the first Sub-DAC outputs to generate a first summed output, the output of the first DAC being equal to the first summed output, the first summed output being proportional to a moving average of the first Sub-DAC outputs; a second DAC to receive a second sample stream and to generate a second DAC output, the second sample stream being representable as second sub-streams that are interleaved with each other, the second DAC comprising a plurality of second Sub-DACs, each second Sub-DAC of the plurality of second Sub-DACs sampling a respective second sub-stream as a function of a respective second clock signal, each second Sub-DAC generating a second Sub-DAC output, the second DAC further comprising a second summation device to receive and sum together the second Sub-DAC outputs to generate a second summed output, the output of the second DAC being equal to the second summed output, the second summed output being proportional to the moving average of the second Sub-DAC outputs; and a multiplexer unit to obtain the first DAC output and the second DAC output, the multiplexer unit to calculate a complementary output from the first DAC output to obtain a complementary first DAC output and a complementary output from the second DAC output to obtain a complementary second DAC output, the multiplexer unit to generate an interleaved output signal that contains a repeating sequence defined by: the first DAC output, the complementary second DAC output, the complementary first DAC output, and the second DAC output, the first DAC and the second DAC being clocked by a local oscillator, the repeating sequence spanning a single period of the local oscillator, the system having a frequency transfer function that depends on the moving average of the first Sub-DAC outputs and on the moving average of the second Sub-DAC outputs. |
