Switched Capacitor Divider for Fine Differential Circuit Tuning
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Solution Overview
Problem
Existing digitally controlled oscillators (DCOs) face challenges in achieving fine frequency resolution due to the need for extremely small capacitance steps, which is difficult to achieve without compromising signal quality or requiring large capacitors for voltage dividers, and the sensitivity is often non-linear and dependent on transistor parameters.
Innovation Solution
A switched capacitor arrangement using capacitive voltage dividers across a differential resonator, where two capacitors of equal size are series connected between differential nodes, allowing for small signal voltages without large capacitor ratios, and the switch connected to the middle node experiences reduced signal current flow, enabling high-resolution tuning without relying on transistor parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If extremely small capacitance steps are used to achieve fine frequency resolution, then frequency resolution is improved, but signal quality deteriorates and transistor parameter dependence increases
Solution Approach 1:
A capacitive voltage divider is introduced as an intermediary between the control signal and the tuning capacitor. This divider attenuates the control voltage, allowing small capacitance changes to produce fine frequency steps while keeping the actual voltage across the tuning capacitor small enough to maintain signal quality and avoid transistor parameter dependence
Solution Approach 2:
The patent changes the voltage parameter in the control path by using a capacitive voltage divider to scale down the control voltage. This allows the system to achieve fine frequency resolution through small capacitance variations without applying large voltages that would degrade signal quality or increase transistor parameter sensitivity
2Measurement precision
If large capacitors are used in voltage dividers to achieve high attenuation, then frequency resolution is improved, but device area increases
Solution Approach 1:
Instead of using large capacitor values to achieve the required attenuation, the patent changes the approach by using a ratio-based capacitive divider where the attenuation is determined by the ratio of two smaller capacitors. This achieves the same voltage attenuation effect with much smaller absolute capacitor values, reducing the required device area
3Ease of operation
If conventional switched capacitor arrangements are used, then frequency tuning is achieved, but tuning linearity deteriorates and transistor parameter dependence increases
Solution Approach 1:
The capacitive voltage divider acts as a mediator that linearizes the tuning relationship. By attenuating the control voltage before it reaches the tuning capacitor, the divider ensures that the frequency change is proportional to the control signal, improving tuning linearity and reducing dependence on transistor parameters like transconductance variations
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 approach allows for precise frequency tuning with a limited range of capacitor sizes, reducing the need for small or large capacitors, achieving fine capacitance steps and frequency resolution while maintaining signal quality and independence from transistor parameters, resulting in improved tuning sensitivity and linearity.
Implementation Method 1
a first capacitor (C1) coupled between a first node (211) and a second node (212), a second capacitor (C2) coupled between the second node (212) and a third node (213)... The switched capacitor arrangement is based on using capacitive voltage dividers across a differential resonator of a differential circuit
Implementation Method 2
the switch connected to the middle node experiences reduced signal current flow, enabling high-resolution tuning without relying on transistor parameters
Data Source
AI summary
A switched capacitor arrangement for tuning a differential circuit is disclosed. The switched capacitor arrangement comprises a first node, a second node and a third node. The switched capacitor arrangement further comprises a first capacitor coupled between the first node and the second node, a second capacitor coupled between the second node and the third node, and a first switch branch comprising a first switch coupled between the second node and a signal ground node. The first switch has an on state and an off state. The first node and third node are configured to be connected to respective differential nodes of the differential circuit. The switched capacitor arrangement is configured to tune the differential circuit by controlling the state of the first switch.