Folded Cascode Overload Recovery With Output Voltage Control
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Solution Overview
Problem
Folded cascode amplifiers face challenges in recovering quickly from overload conditions due to parasitic capacitance and the need for transistors to operate in the saturation region, leading to slow recovery times in high-speed analog or mixed signal circuits.
Innovation Solution
An improved cascode amplifier with an overload recovery circuit (ORC) that generates an overload current to rapidly restore transistors to the saturation region, including a makeup current circuit and a controller to manage output voltage during overloads, enabling rapid recovery from overload conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If transistors are allowed to operate in triode region during overload, then output voltage can swing freely, but recovery time becomes excessively long
Solution Approach 1:
The controller proactively controls the output voltage during overload conditions to prevent excessive discharge of parasitic capacitances. By applying preliminary anti-action through voltage control, the system counteracts the tendency toward prolonged recovery, enabling faster return to saturation region operation without uncontrolled output swings
Solution Approach 2:
The controller monitors the overload condition and provides feedback control to manage the output voltage. This feedback mechanism ensures that the output voltage is maintained within acceptable ranges during overload, preventing complete discharge of capacitances and enabling faster recovery while maintaining operational control
2Ease of manufacture
If parasitic capacitances are allowed to discharge during overload, then transistor operation is simplified, but recovery time increases due to recharging requirements
Solution Approach 1:
The controller applies preliminary anti-action by controlling the output voltage during overload to limit the discharge of parasitic capacitances. This prevents complete energy depletion, allowing transistors to maintain simplified operation while ensuring that capacitances retain sufficient charge for rapid recovery, thus reducing the time penalty
Solution Approach 2:
The voltage control mechanism provides beforehand cushioning by maintaining minimum voltage levels during overload. This cushioning effect ensures that parasitic capacitances are not fully discharged, providing a buffer that enables faster recovery without compromising the simplified transistor operation during the overload event
Data Source
AI summary
In a method and apparatus for rapidly recovering an improved amplifier from an overload condition, a cascode amplifier (CASA) having a pair of inputs and an output is coupled to an overload recovery circuit (ORC). The pair of inputs is coupled to receive a differential input signal. A deviation in the differential input signal that is greater than a threshold causes a deviation in a current provided to at least one transistor included in the CASA. The deviation in the current causes the CASA to operate in an overload condition (OC). The ORC includes a makeup current circuit operable to generate an overload current in response to the OC and a controller operable to control a voltage at the output during the OC. The controller coupled to the makeup current circuit provides the overload current to the CASA to enable the rapid recovery from the OC.