| 摘要 |
PURPOSE: A digital down-converter and receiver is provided to simplify the construction of a mixer, a local oscillator and a decimation filter required to be processed at an ultra-high speed and reduce a power consumption by installing the first mixer for converting a frequency of a reception signal into the first IF signal and the second mixer for converting the first IF signal into the first IF signal, a detecting frequency, and making it complex. CONSTITUTION: The first multiplier(201) receives a digital IF signal fl(t) of a frequency Fd1 and a local signal c(t) of a frequency Fc1 outputted from a local oscillator(202), multiplies the inputted signals and outputs a digital IF signal f2(t). A decimation filter(203) inputs an output signal f2(t) of the first mixer(201), restrains a signal of a frequency(Fd1+Fc1), an non-target signal of the input signal f2(t), and down-samples the input signal f2(t) to a sampling frequency Fs2 of 1/8 of the frequency Fs1. An AGC(automatic gain control) amplifier(204) inputs a digital IF signal f2(t), amplifies it according to a control signal provided from a baseband circuit, and outputs it to the second mixer(205). The second mixer(205) multiplies the digital IF signal f2(t) amplified by the AGC amplifier(204) and 1/4 of the sampling frequency, and converts it into a baseband signal fb(t) of a detecting frequency for a detecting processing. Rolloff filters(206a,206b) rolloff-shape the baseband signal fb(t) and outputs complexing signals of an in-phase component I and an orthogonal component Q. A selector(205a) cycles and selects values for the multiplication, the values of cosine wave oscillated by the local oscillator. A selector(205b) cycles and selects values for multiplication, the values of sine wave oscillated by the local oscillator.
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