3-Stage Amplifier Slew Detection for Faster Settling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Three-stage amplifiers, particularly chopper-stabilized ones with notch filtering, face challenges in achieving fast output slewing rate and settling time due to the averaging function of notch filters treating large, fast-changing signals as errors, which increases settling time during large signal slewing operations.
Innovation Solution
Incorporating a slew detection current generation circuit that converts the detection current into a control signal to short-circuit output conductors and prevent signal charge buildup on capacitances during slewing, thereby reducing charge accumulation and enhancing slewing rate and settling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a notch filter is added to filter ripple voltage, then output ripple is reduced, but settling time increases during large signal slewing
Solution Approach 1:
The notch filter is configured to dynamically disable its averaging function during large signal slewing conditions. When the amplifier is slewing, the notch filter detects the large differential voltage and disables charge accumulation on its internal capacitors, allowing fast signal passage. When slewing is complete and the amplifier enters the settling phase, the notch filter re-enables its averaging function to filter ripple. This dynamic switching resolves the contradiction by making the filter adaptive to different operational states.
Solution Approach 2:
The effective capacitance of the notch filter is changed based on operating conditions. During slewing, the notch filter's internal switches disconnect the integrating capacitors from the signal path, effectively reducing the capacitance to near zero. During settling, the capacitors are reconnected to provide ripple filtering. This parameter change allows the system to achieve both fast slewing response and effective ripple rejection.
2Measurement precision
If chopper stabilization is used to reduce offset voltage and flicker noise, then DC accuracy is improved, but output ripple increases due to chopping frequency components
Solution Approach 1:
A notch filter is introduced as an intermediary component between the chopper-stabilized amplifier stages. This notch filter is specifically designed to reject frequency components at the chopping frequency and its harmonics. The filter acts as a mediator that allows the benefits of chopper stabilization (offset reduction, flicker noise reduction) to be achieved while simultaneously eliminating the harmful ripple effects generated by the chopping switches.
3Loss of time
If the chopping frequency is increased to reduce settling time, then settling time is improved, but parasitic capacitance effects increase and implementation difficulty increases
Solution Approach 1:
Instead of increasing chopping frequency to reduce settling time, the invention dynamically controls the notch filter's internal switches to disable charge accumulation during slewing. This dynamic control allows the system to achieve fast settling without changing the fundamental chopping frequency, thereby avoiding the increased parasitic effects and implementation complexity that would result from higher frequency operation.
Data Source
AI summary
An operational amplifier (1B) amplifies an input signal (Vin) to produce an output signal (Vout), and includes a 3-stage amplifier (1C) including a first amplifier stage (2) receiving the input signal, a second amplifier stage (3) driven by the first amplifier stage (2), and a third amplifier stage (4) driven by the second amplifier stage to produce the output signal. A slew detection current (Idetect) is generated when the input signal (Vin) exceeds a certain magnitude, and is converted to a control signal (41) that operates a switch (MN0) to short-circuit output conductors of the first amplifier stage to prevent signal charge from building up on capacitances associated with the output of the first amplifier stage during slewing. The three stage amplifier can be a chopper-stabilized, notch-filtered amplifier.