| 摘要 |
An IQ modulator in which digital I (155) and Q (153) signals, which are quadrature representations of a modulating function, are connected into corresponding analogue I (165) and Q (163) signals using a first (156, 135) and second (154, 135) sigma-delta Digital-to-Analogue Converter (DAC). The analogue I and Q signals are then combined with analogue quadrature representations of a carrier signal (160) using two multiplying circuit elements (166, 164) and an adding circuit element (168) to form an output signal substantially at the same frequency as the carrier signal but modulated by the modulating function. Each sigma-delta DAC includes both an adder having a carry output which toggles between a high and a low level at a rate much higher than the bandwidth of the analogue signal to be generated, and a low pass filter arrangement (135).
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