4th Order LC-Based Sigma Delta Modulators

Area of Science:

• Electrical Engineering
• Signal Processing
• Radio Frequency (RF) Engineering

Background:

• Sigma Delta Modulators (ΣΔM) utilizing LC resonators are suitable for Software-Defined Radio (SDR) due to their narrow band conversion characteristics.
• Existing ΣΔM topologies face performance degradation from noise and nonlinearities.

Purpose of the Study:

• To present a design methodology for high-order, single-block, LC-based ΣΔMs.
• To address performance limitations in current ΣΔM designs for SDR applications.

Main Methods:

• A numerical approach was used to establish equivalence between continuous-time and discrete-time loop gain.
• Finite Impulse Response Digital-to-Analog Converters (FIRDAC) were employed to define loop gain coefficients.
• Simulations of continuous bandpass LC ΣΔMs were conducted at a 432 MHz center frequency and 1.72 GHz sampling frequency.

Main Results:

• Three distinct 4th-order LC-based ΣΔMs were designed: Gm-LC, Magnetically Coupled, and Capacitively Coupled.
• Maximum Signal-to-Noise Ratios (SNR) of 51.39 dB, 48.48 dB, and 46.50 dB were achieved, respectively, within a 4 MHz bandwidth.
• The proposed modulators demonstrate improved performance over existing state-of-the-art designs.

Conclusions:

• The presented design methodology effectively yields high-performance LC-based ΣΔMs for SDR.
• The developed modulators offer a viable solution for achieving high SNR in RF applications.
• Further research can explore optimizations for even greater noise and nonlinearity mitigation.