Multi-Stacked Amplifier Gain Switching With Cascode Voltage Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Amplifiers with adjustable gain using multi-stacked cascode circuits face issues with large voltage drops across turned-off cascode transistors due to operation of other amplifiers, leading to increased failure rates and costs.
Innovation Solution
Implementing a technique where the gate bias voltages of cascode transistors are set to optimal turn-off voltages and AC coupling capacitors are selectively coupled or decoupled from ground to minimize voltage drops across cascode transistors when turning off amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If gate bias voltages of cascode transistors are grounded to turn off amplifiers, then the selected amplifier is effectively turned off, but large voltage drops appear across the terminals of the turned-off cascode transistors
Solution Approach 1:
The patent applies parameter changes by transitioning the gate bias voltage of the first cascode transistor from a grounded state (0V) to a raised voltage state (e.g., half of VDD or full VDD) when the amplifier is turned off. This parameter change in the gate bias voltage directly reduces the voltage drop across the cascode transistor terminals while maintaining the amplifier's turned-off state, thereby resolving the contradiction between ease of operation and harmful voltage drops.
Solution Approach 2:
The patent implements preliminary anti-action by proactively raising the gate bias voltage of the first cascode transistor before or simultaneously with turning off the amplifier. This preliminary action prevents the harmful large voltage drops from occurring across the cascode transistor terminals, countering the potential damage before it can affect the circuit reliability.
2Ease of operation
If large voltage drops occur across turned-off cascode transistors, then the amplifier can be turned off, but the breakdown limits of the turned-off devices are exceeded, increasing failure rate and cost
Solution Approach 1:
The patent changes the gate bias voltage parameter of the first cascode transistor from ground (0V) to a raised voltage level (e.g., VDD/2 or VDD) when the amplifier is disabled. This parameter modification ensures that the voltage drop across the cascode transistor terminals remains within safe breakdown limits while preserving the amplifier's turned-off state, thus maintaining both operational flexibility and device reliability.
Solution Approach 2:
The patent applies beforehand cushioning by pre-raising the gate bias voltage of the first cascode transistor to a protective voltage level before the amplifier is fully turned off. This cushioning voltage protects the cascode transistor from excessive voltage stress that would otherwise occur during the turn-off transition, preventing breakdown and reducing failure rates.
Data Source
AI summary
Techniques for providing adjustable gain in an amplifier. In an aspect, a composite amplifier having adjustable gain includes a plurality of amplifiers coupled in parallel, wherein each of the amplifiers may be turned on or off to adjust the overall gain of the composite amplifier. Each amplifier may include an input transistor and at least two cascode transistors. To turn each amplifier off, the gate voltage of a second or lowermost cascode transistor coupled to the input transistor may be grounded, and the gate voltage of a first cascode transistor coupled to the output voltage may be coupled to a first turn-off voltage to reduce the drain-to-gate voltage drop across the first cascode transistor. Further aspects provide for decoupling a capacitor coupled to the gates of the cascode transistors from AC ground when the amplifier is turned off.