Digital Compensation Filter for Faster Analog Transmitter Response
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing process transmitters face challenges in achieving fast response times due to the time constants of analog circuit elements in digital-to-analog converters and I/O circuits, which hinder the capture of transient process variable changes.
Innovation Solution
Implementing a compensating filter that offsets the frequency-domain transfer function of the output analog circuitry by using a filter with a transfer function that is the inverse of the analog circuit's transfer function, reducing the response time while maintaining signal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a digital-to-analog converter with analog output circuitry is used in a process transmitter, then the transmitter can provide analog output signals for communication, but the time constant of the analog circuit elements limits the response speed and prevents capture of transient process variable changes
Solution Approach 1:
The patent applies preliminary action by pre-compensating the digital signal before it reaches the analog output circuitry. A compensating filter is implemented in the digital domain to pre-distort the signal in a way that counteracts the known time constant effects of the subsequent analog circuitry. This allows the system to achieve faster effective response times because the compensation is applied in advance, before the signal passes through the limiting analog components.
Solution Approach 2:
The patent changes the parameter domain by moving the compensation operation from the analog domain to the digital domain. By implementing the compensating filter digitally, the system can adjust filter coefficients and transfer function parameters without being constrained by analog component tolerances and drift. This digital parameter control enables precise compensation that maintains signal stability while improving response speed.
2Speed
If the analog output circuitry time constant is reduced to increase response speed, then transient changes can be captured faster, but signal stability and noise performance deteriorate
Solution Approach 1:
The patent introduces a digital compensating filter as an intermediary between the digital signal source and the analog output circuitry. This intermediary process models the analog circuitry's transfer function and applies inverse compensation to the digital signal. The compensating filter acts as a mediator that prepares the signal in advance, allowing the analog circuitry to operate at its natural time constant while achieving improved effective response performance without compromising signal stability.
3Speed
If digital filtering is applied to compensate for analog circuitry transfer function, then the response time is improved, but the device complexity increases
Solution Approach 1:
The patent replaces what would traditionally require complex analog filtering circuitry with digital filtering implemented in software or firmware. By substituting the mechanical/electrical analog filter with a digital algorithm, the system achieves the same compensation function with greater precision and flexibility. The digital implementation allows for easy adjustment of filter parameters without physical component changes, reducing overall system complexity while maintaining improved response performance.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A process transmitter (200) includes a circuit producing a plurality of digital values representing magnitudes for an analog signal and a filter (213) receiving the plurality of digital values and producing a plurality of filtered digital values. Output analog circuitry (216) in the process transmitter (200) is configured to receive the filtered digital values and output an analog signal on a communication channel (204) of the process transmitter (200). The output analog circuitry (216) has a transfer function and the filter (213) has a transfer function. The transfer function of the filter (213) at least partially offsets the transfer function of the output analog circuitry (216).