Digitally Controlled Oscillator DAC Topology for Current Peak Noise
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Solution Overview
Problem
Digitally controlled oscillators face noise issues due to rapid current changes in resistor groups when switch changeover occurs, leading to degraded noise characteristics, especially in high-resolution oscillators with 12 bits or more, where noise is difficult to reject with conventional filters and may require large capacitors, hindering miniaturization.
Innovation Solution
The implementation of a digitally controlled oscillator with a resistor voltage-dividing type D/A conversion circuit that minimizes current peak noise by separating active elements from the reference voltage path, using operational amplifiers to reduce noise propagation, and allowing for miniaturization even with high-resolution signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an R-2R type D/A converter with changeover switch is used, then the circuit configuration is simplified, but noise is generated due to rapid current changes when the switch is switched, degrading noise characteristics
Solution Approach 1:
The patent extracts the changeover switch from the reference voltage path by introducing a buffer amplifier between the reference voltage and the resistor group. This separation removes the source of rapid current changes from the critical signal path, eliminating the noise generation mechanism while preserving the R-2R converter's simplified structure
Solution Approach 2:
A buffer amplifier is introduced as an intermediary element between the reference voltage and the resistor group. This mediator isolates the reference voltage path from the switching operations, preventing rapid current changes from occurring in the reference path while still enabling the D/A conversion function
2Object-affected harmful factors
If a low-pass filter is used to reduce noise, then noise on the control signal is reduced, but a large capacitor is required, failing to meet miniaturization needs
Solution Approach 1:
The buffer amplifier performs preliminary action by preventing rapid current changes before they occur in the first place. By isolating the reference voltage path from switching operations ahead of time, the noise is prevented at its source, eliminating the need for subsequent noise filtering and large capacitors
3Measurement precision
If high-resolution digital signal of 12 bits or more is used, then the oscillator precision is improved, but the noise generated due to rapid current change becomes a serious problem
Solution Approach 1:
The patent extracts the changeover switch from the reference voltage path, separating the high-resolution digital switching operations from the analog reference voltage. This allows 12-bit or higher resolution D/A conversion to proceed without generating noise in the reference path, as the switching occurs only in the isolated digital domain
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces noise on the output signal, enhancing frequency accuracy and enabling the creation of compact, high-resolution digitally controlled oscillators capable of temperature compensation.
Implementation Method 1
a first D/A conversion circuit of resistor voltage-dividing type that generates a voltage between the first reference voltage and the second reference voltage
Data Source
AI summary
An oscillator includes a control voltage generator that generates a control voltage between a first reference voltage and a second reference voltage with a digital signal, and a voltage controlled oscillation circuit that outputs a signal at a frequency in response to the control voltage. The control voltage generator includes a first D/A conversion circuit of resistor voltage-dividing type that generates a voltage between the first reference voltage and the second reference voltage.