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We present a 4th-order, 3-bit, 4.3 GHz continuous-time bandpass ΔΣ modulator (CT-DSM) that can directly digitize a 1.3-GHz IF signal. We used the impulse-invariant transform to design the CT-DSM, which has a similar NTF (noise transfer function) as an idealized discrete-time modulator despite up to 1.6 clock delays in its feedback loop paths. The part was fabricated using InP HBT technology, and has a measured SNDR of 39 dB in a 200 MHz bandwidth.
Date of Conference: 21-24 Sept. 2003