Programmable Quadrature Divider Using Divide-by-3 Phase Correction
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Solution Overview
Problem
Existing local oscillator designs in radio receivers face challenges in achieving a wide VCO tuning range, particularly in integrated transceiver circuits for cellular telephones, where a single design must accommodate multiple frequency bands, and frequency dividers that divide by three are not usable due to the requirement for quadrature signals with a 90-degree phase difference.
Innovation Solution
A programmable frequency divider is introduced, incorporating a divide-by-three circuit, a delay circuit, and a feedback circuit to generate fifty percent duty cycle quadrature signals that differ by ninety degrees, allowing the frequency divider to operate effectively by three, and automatically corrects for variations due to temperature, voltage, and fabrication changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a wide VCO tuning range is used to accommodate multiple frequency bands, then the local oscillator can operate across various frequency bands, but the VCO design becomes difficult to realize and the device complexity increases
Solution Approach 1:
The frequency division is segmented into multiple paths: a divide-by-3 path and a divide-by-2 path. The divide-by-3 path further segments the output into three phases (0°, 120°, 240°), which are then combined to produce quadrature outputs (0° and 90°). This segmentation allows the VCO to operate at a fixed frequency while achieving multiple output frequencies through different division ratios.
Solution Approach 2:
The frequency divider is designed to be programmable, allowing it to function as either a divide-by-3 or divide-by-2 unit based on control signals. This multi-functionality enables the same hardware to support multiple frequency bands without requiring multiple dedicated VCOs or frequency dividers, thereby reducing overall device complexity.
2Device complexity
If a divide-by-three frequency divider is used to reduce VCO tuning range, then the VCO design becomes easier, but quadrature signals with 90-degree phase difference cannot be generated
Solution Approach 1:
The patent merges the divide-by-3 output (providing 0°, 120°, 240° phases) with a delay element to create the quadrature pair. Specifically, the 120° phase signal is delayed by 30° to produce the 90° quadrature signal. This combining approach allows both divide-by-3 functionality and quadrature output generation within the same circuit.
Solution Approach 2:
A delay element acts as an intermediary between the divide-by-3 circuit output and the final quadrature output. The delay element converts the 120° phase signal into a 90° phase signal by introducing a 30° delay, thereby enabling quadrature signal generation without requiring a traditional divide-by-2 frequency divider.
3Device complexity
If the frequency divider outputs are used directly, then the circuit is simple, but the duty cycle is not 50% and the phase relationship is not suitable for quadrature applications
Solution Approach 1:
The patent employs a feedback mechanism where the phase relationship between the divided output signals is monitored and used to control the delay element. The feedback ensures that the delay is precisely adjusted to achieve the correct 90° phase difference, maintaining high phase accuracy despite variations in operating conditions such as temperature and voltage.
Data Source
AI summary
A local oscillator includes a programmable frequency divider coupled to the output of a VCO. The frequency divider can be set to frequency divide by three. Regardless of the divisor, the frequency divider outputs quadrature signals (I, Q) that differ from each other in phase by ninety degrees. To divide by three, the frequency divider includes a divide-by-three frequency divider. The divide-by-three frequency divider includes a divide-by-three circuit, a delay circuit, and a feedback circuit. The divide-by-three circuit frequency divides a signal from the VCO and generates therefrom three signals C, A′ and B that differ from each other in phase by one hundred twenty degrees. The delay circuit delays signal A′ to generate a delayed version A of the signal A′. The feedback circuit controls the delay circuit such that the delayed version A (I) is ninety degrees out of phase with respect to the signal C (Q).