Output Driver Filter Architecture for Low RF Spur Noise
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Solution Overview
Problem
Integrated circuits face noise issues due to proximity of input and output signal paths, leading to radio frequency energy coupling that degrades RF performance, with existing solutions being ineffective from cost and space perspectives.
Innovation Solution
An apparatus comprising a filter with a feedback loop and a digital output pad, using an operational amplifier and low pass filter to reduce impulse current coupling, and an output stage with MOSFETs and a control circuit to limit current flow and prevent rail-to-rail swinging, along with a control circuit to manage shoot-through current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a digital pad driver is placed in proximity to an RF input signal path, then the IC can achieve higher integration density and smaller form factor, but RF energy couples from the digital driver to the input signal path degrading RF performance
Solution Approach 1:
An RC filter network is introduced as an intermediary component between the digital output pad driver and the external digital output signal. This filter acts as a mediator that allows the digital signal to pass through while blocking RF energy from coupling into adjacent RF input signal paths, thus resolving the interference problem while maintaining the high integration density
2Object-affected harmful factors
If an RC filter is added to reduce RF interference, then RF performance is improved, but the component count and circuit complexity increase
Solution Approach 1:
The RC filter network is merged with the existing output pad driver circuit by sharing common nodes and signal paths. The filter components are integrated into the driver's output stage rather than being added as separate external components, thus reducing overall circuit complexity while maintaining RF interference reduction capability
Solution Approach 2:
The RC filter network serves multiple functions simultaneously: it filters RF interference from the digital output signal, provides impedance matching, and stabilizes the output driver. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in component count
3Object-affected harmful factors
If the output signal is prevented from rail-to-rail swinging, then RF interference is reduced, but the signal dynamic range is limited
Solution Approach 1:
The RC filter network changes the signal parameters by filtering high-frequency RF components while preserving the baseband digital signal characteristics. The filter's frequency response is designed to attenuate RF frequencies above the signal bandwidth, effectively reducing RF interference while maintaining adequate signal dynamic range for reliable digital communication
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
The solution effectively reduces RF interference by filtering outgoing signals to digital output pads, maintaining the output current at a predetermined level and limiting current flow, thereby enhancing RF performance while minimizing component count and size.
Implementation Method 1
a first capacitor coupled between an output of the filter and a first input terminal of the filter; a second capacitor coupled between the first node and a reference voltage node
Implementation Method 2
a first resistor coupled to a second resistor at a first node, the second resistor coupled to the first input terminal of the filter, and a third resistor coupled between the output of the filter and the first node
Implementation Method 3
the filter comprises an operational amplifier
Implementation Method 4
a first resistor coupled to a second resistor at a first node
Implementation Method 5
a second capacitor coupled between the first node and a reference voltage node
Implementation Method 6
a first metal oxide semiconductor field effect transistor (MOSFET) having a gate terminal to receive the driving signal and a second terminal to output the filtered signal; and a second MOSFET having a gate terminal to receive a control signal
Data Source
AI summary
In one embodiment, an integrated circuit includes: a first input pad to receive a radio frequency (RF) signal; a radio receiver to process the RF signal and output a digitally processed signal; an analog filter to receive a digital signal via an input signal path and output a drive signal via an output signal path; and a first output pad coupled to the output signal path to output a filtered digital signal based on the drive signal.