Image Signal Amplifier Circuit for Output Sag Compensation
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Solution Overview
Problem
Existing image signal amplifying circuits face challenges in miniaturizing and cost-reducing the output capacitor while preventing signal distortion and sag, particularly due to the requirement for large electrolytic capacitors and the limitations of inverting amplifier circuits which also increase circuit size.
Innovation Solution
The implementation of a second-order high pass filter with a Q value greater than one at the input stage, using a non-inverting amplifier circuit with an operational amplifier, input capacitors, and feedback resistances to correct distortion in the output high pass filter, allowing for a smaller output capacitor and reduced component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a first-order high pass filter with a large output capacitor is used, then the cut-off frequency can be set low (about 1 Hz) to output image signals without distortion, but the capacitor size becomes large (about 1000 μF) requiring expensive electrolytic capacitors
Solution Approach 1:
The patent divides the single first-order high pass filter into two cascaded second-order high pass filters. The first filter (with capacitors C1, C2 and resistors R1, R2) and the second filter (with capacitors C3, C4 and resistors R3, R4) work together to achieve the desired low cut-off frequency. This segmentation allows each filter stage to use smaller capacitors while maintaining the overall filtering performance, eliminating the need for large electrolytic capacitors.
Solution Approach 2:
The patent transitions from a first-order filter to second-order filters, changing the order (dimension) of the filtering system. This dimensional change in the filter order provides steeper roll-off characteristics and allows achieving the same cut-off frequency with smaller capacitor values, thereby reducing the overall capacitor size and cost.
2Quantity of substance
If feedback capacitors and resistors are added to reduce output capacitor size, then the capacitance value can be reduced to about 1/10, but electrolytic capacitors are still required and cost reduction is insufficient
Solution Approach 1:
Instead of adding feedback components to a single filter stage, the patent segments the filtering function into two independent second-order high pass filter stages. Each stage is designed with its own capacitors and resistors, allowing the output capacitor to be significantly smaller without requiring feedback paths or electrolytic capacitors. The segmented architecture achieves size reduction through distributed filtering rather than feedback-based compensation.
3Adaptability or versatility
If an inverting amplifier circuit is used to widen input dynamic range, then the dynamic range improves, but the circuit size enlarges and requires additional inverting amplifier stages
Solution Approach 1:
The patent extracts the signal inversion function from the amplifier circuit and handles it separately through the dual second-order high pass filter configuration. By processing the signal through two cascaded filter stages with appropriate phase compensation, the circuit achieves wide input dynamic range without requiring traditional inverting amplifier stages, thereby reducing overall circuit size and complexity.
4Reliability
If electrolytic capacitors with large capacitance values are used, then the cut-off frequency requirement is met, but the cost increases and miniaturization is prevented
Solution Approach 1:
The patent segments the total capacitance requirement across multiple smaller capacitor components in the two cascaded filter stages. Instead of using a single large electrolytic capacitor, the filtering function is distributed across several smaller capacitors (C1, C2, C3, C4) that can be implemented as inexpensive chip capacitors, thereby reducing manufacturing cost while maintaining frequency response accuracy.
Solution Approach 2:
The patent replaces expensive electrolytic capacitors with cheaper chip capacitor alternatives. By using the segmented second-order filter architecture, the circuit achieves the required frequency response using inexpensive, readily available chip capacitors instead of costly electrolytic capacitors, significantly reducing manufacturing cost and enabling miniaturization.
Data Source
AI summary
An image signal amplifying circuit comprises: an amplifier circuit for amplifying an image signal; an output capacitor and a resistance, both being serially connected between an output node of the amplifier circuit and an output terminal; and a second-order high pass filter having a value of Q larger than one, the second-order high pass filter being provided at a preceding stage of the amplifier circuit, wherein distortion to correct a sag arising in a high pass filter on an output side, the high pass filter including the output capacitor and the resistance, is caused in the input image signal by a characteristic of the second-order high pass filter.