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Why continuous time Delta Sigma as a starting point

•  Continuous‑time Delta‑Sigma ADCs are often the best entry point for learning Delta‑Sigma conversion because their behavior is far more intuitive to visualize and explore than discrete‑time architectures. In a continuous‑time loop, the integrators, feedback paths, and stability dynamics can be observed directly as real analog signals, making it easier to understand how noise shaping, loop order, and non‑idealities interact. This hands‑on visibility helps new learners build a strong mental model of how a Delta‑Sigma modulator actually behaves before moving on to the more abstract, clock‑driven world of discrete‑time designs. By starting with continuous‑time, you gain a clearer foundation that makes the transition to discrete‑time—and eventually to high‑performance hybrid architectures—much more natural. 

1. Inherent Anti-Aliasing:
   CT ΔΣMs directly interface with continuous analog signals, creating a natural low-pass filtering effect. This reduces aliasing without the need for additional analog pre-filters, which simplifies the system design.
2. High Signal Fidelity (SNR and SFDR):
   By leveraging continuous-time loop filters, CT ΔΣMs can achieve better SNR and spurious-free dynamic range (SFDR) than purely discrete-time implementations for the same oversampling ratio. The continuous-time integration smooths quantization noise and enhances noise shaping.
3. Ease of Implementation in Discrete Designs:
   Despite being continuous-time, these topologies can be efficiently modeled and experimented with in discrete designs. 
4. Reduced Settling Requirements:
   Continuous-time filters often relax the strict settling time requirements seen in discrete-time ΔΣMs, allowing improved linearity and reduced distortion in practical implementations.

1. Timing Sensitivity:
   The analog integrators of a CT ΔΣM are sensitive to clock and timing mismatches. Any asymmetry between rising and falling edges or jitter in the integration period directly affects the measured values and can degrade signal fidelity (SFDR) by several dB.
2. Edge-Dependent Distortions:
   Slight deviations in the timing of signal edges, even in the range of picoseconds, can introduce harmonic distortion or spurious tones. For this reason input integration amplifiers require excess bandwidth to settle the error voltage as quickly as possible during the integration period.