Programmable Gain Amplifier Compensation for Constant Bandwidth
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional programmable gain amplifiers suffer from a reduction in bandwidth as gain increases, leading to undesirable signal deterioration in applications like video tuners and communication systems, where stable bandwidth is required under varying gains.
Innovation Solution
A programmable gain amplifier with a variable compensating capacitor that adjusts the dominant-pole frequency of the operational amplifier, maintaining constant bandwidth across variable gains by dynamically adjusting the capacitance of the feedback capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the gain of the programmable gain amplifier is increased by adjusting the feedback factor, then the amplification capability is improved, but the bandwidth is reduced
Solution Approach 1:
The patent applies dynamics by making the pole frequency adjustable rather than fixed. The operational amplifier's pole frequency is dynamically changed based on the feedback factor setting, allowing the system to adapt its frequency characteristics to maintain constant bandwidth while varying gain. This is achieved through a variable compensating capacitor that adjusts the dominant pole location in the frequency response.
Solution Approach 2:
The patent changes the physical parameter of pole frequency to resolve the contradiction. By adjusting the pole frequency parameter in response to feedback factor changes, the system maintains a constant relationship between gain and bandwidth. The variable compensating capacitor enables continuous adjustment of the pole frequency parameter to compensate for bandwidth variations that would normally occur with gain changes.
2Device complexity
If a conventional operational amplifier with fixed pole frequency is used, then the circuit structure is simple, but the bandwidth varies with gain changes causing signal deterioration
Solution Approach 1:
The patent introduces dynamics by making the pole frequency adjustable through a variable compensating capacitor. This dynamic adjustment mechanism allows the operational amplifier to adapt its frequency response characteristics to maintain constant bandwidth, thereby preventing signal deterioration while keeping the overall circuit structure relatively simple.
Solution Approach 2:
The patent applies feedback by using the feedback factor information to control the adjustment of the pole frequency. The system monitors the feedback factor setting and automatically adjusts the compensating capacitor to maintain the desired bandwidth, creating a closed-loop control mechanism that ensures signal quality across different gain settings.
Data Source
AI summary
A programmable gain amplifier includes an operational amplifier coupled thereto a plurality of resistors to perform a feedback control, thereby rendering a closed-loop gainAf(s)=A(s)1+A(s)·β,where β is a feedback factor determined by the resistance of the resistors and A(s) is an open-loop gain of the operational amplifier. The operational amplifier includes a first-stage amplifying circuit, a second-stage amplifying circuit, and a compensating capacitor coupled to an output end of the first-stage amplifying circuit and having an equivalent capacitance variable to adjust a dominant-pole frequency of the open-loop gain of the operational amplifier.