The implementation of a Cross-Coupled LC-VCO (Inductor Capacitor Voltage-Controlled Oscillator) with a frequency divider is driven by its performance and adaptability. These VCOs provide excellent frequency stability, low phase noise, and a wide tuning range, making them ideal for precision-demanding applications like RF and wireless communication. Their energy efficiency suits battery-powered devices, while the integration of a frequency divider supports frequency multiplication, division, and synchronization in tasks such as clock generation and phase-locked loops. Key design considerations include phase noise, tuning range, power consumption, center frequency, and figure of merit, with trade-offs balanced to meet project requirements.
This project aims to design a 60GHz Cross-Coupled LC Voltage-Controlled Oscillator (VCO) integrated with a Divider Chain and Buffer, ensuring proper functionality through electromagnetic (EM) simulations in 130nm SiGe BiCMOS technology. The process covers all stages, from initial design to post-layout simulations, EM analysis, and design optimization.
The Voltage-Controlled Oscillator (VCO) is linked to a VCO buffer, and from there, its output is directed to a static frequency divider. This divider efficiently halves the frequency, resulting in an output that is then routed to the divider buffer.
A static frequency divider, utilizing master-slave D flip-flops, reduces an input signal's frequency by a predetermined integer factor. It consists of two flip-flops in series: one acting as the master and the other as the slave. The input signal is connected to the clock input of the master flip-flop. The division ratio is determined by the number of flip-flops; for instance, two flip-flops in series result in a division by 4. As the input clock transitions, the master flip-flop captures its D input and transfers it to the slave on the subsequent edge. The output from the slave flip-flop provides the divided frequency, ensuring precise and synchronous frequency division. This configuration is commonly employed in digital circuits, clock generation, and electronics projects that require accurate frequency division.
A D-latch implemented using emitter-coupled logic (ECL) is described, along with a divide-by-two circuit that uses two ECL D-latches with cross-feedback. To ensure smooth connectivity between all D-latches, the DC levels of the Q and Q Bar outputs are aligned with those of the input D and D Bar signals. Additionally, single emitter followers are used at the output of each D-latch to reduce the supply voltage requirements.
1. Design: During the layout design phase, a detailed physical representation of the circuit is created, with components such as transistors, capacitors, and resistors placed according to the schematic. Special attention is given to current densities within the metal layers, avoiding sharp corners and ensuring a smooth flow of current to prevent issues like electromigration and current crowding, which can impact the chip's long-term reliability.
2. LVS (Layout vs. Schematic) Check: Verified that my layout design correctly matches the schematic diagram in terms of connectivity and node correspondence.
3. Extraction of Parasitics
4. EM Rule Check and Simulation Setup: The RF Pro tool is used to verify the layout against electromagnetic design rules, which include minimum metal-to-metal spacing, via spacing, and other electromagnetic considerations to prevent manufacturing issues and performance problems. Additionally, the EM simulation tool within Cadence is configured by specifying parameters such as the analysis frequency range and input/output ports.
5. Conducted EM Analysis: EM simulations on the layout revealed parasitic effects such as coupling, inductance, and capacitance. To assess their impact, the results were analyzed by examining S-parameters, impedance plots, and other EM simulation data. This analysis provided valuable insights into how parasitic effects influence circuit performance.
6. Repeat if Needed: I iteratively repeated the simulation, optimization, and analysis processes as needed to achieve the desired performance specifications while minimizing parasitic effects.
VCO's Frequency Analysis
Schematic and RC Extracted Tuning Range of LC-VCO
Phase Noise of Cross-Coupled Oscillator
The layout can still be further optimized; this is just a preliminary concept to demonstrate how the design appears when all the blocks are combined.
