Two-Stage Solid State Switch for Fast Isolated Signal Switching
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Solution Overview
Problem
Existing solid state switches used in precision measurement systems have settling times in milliseconds, which are inadequate for sub-microsecond switching requirements, leading to inefficiencies and signal contamination due to charge injection from control circuitry.
Innovation Solution
A solid state switch design incorporating a quick response circuit to rapidly place a solid state device into a conducting state and a sustained response circuit to maintain it, combined with opto-isolation using devices like pulse transformers and optical current sources, along with low pass filters to prevent charge injection, enabling sub-microsecond switching speeds and improved isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solid state switches are used with opto-isolation, then isolation between control circuitry and switched signal is achieved, but settling time increases to milliseconds which is unacceptable for precision measurements
Solution Approach 1:
The gate drive signal is segmented into two distinct components: a fast transient pulse for rapid channel formation and a sustained DC level for maintaining conduction. This segmentation allows the switch to achieve both fast settling time (sub-microsecond) and proper isolation, as each component performs its specific function without interfering with the other's optimization
Solution Approach 2:
The control circuit performs preliminary action by pre-charging the gate capacitance through the fast transient pulse before the main switching event. This preliminary charging reduces the time required for the channel to form during the actual switching operation, thereby reducing settling time while maintaining isolation through the opto-coupler
2Ease of manufacture
If smaller and less expensive solid state switches are used in place of relays, then cost and size are reduced, but settling time increases to milliseconds
Solution Approach 1:
The invention makes the gate drive signal dynamic by using a two-stage control approach: an initial fast transient pulse that rapidly charges the gate to establish conduction, followed by a sustained DC level that maintains the conducting state. This dynamic control enables smaller solid state switches to achieve sub-microsecond settling times comparable to relays, eliminating the millisecond delays that previously made them unsuitable for precision measurements
3Reliability
If solid state devices are used for switching, then reliability is improved compared to mechanical relays, but charge injection from control circuitry contaminates the switched signal
Solution Approach 1:
The harmful charge injection effect is extracted and isolated from the signal path by using an opto-coupler to separate the control circuitry from the switched signal. The control signals remain in the optical domain during transmission, preventing direct electrical coupling and charge injection. Additionally, the gate drive circuit extracts only the necessary fast transient component for channel formation, leaving the signal path free from contamination
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves sub-microsecond switching speeds and excellent isolation, reducing signal contamination and eliminating the need for costly relays in precision measurement systems, allowing for more efficient and accurate measurements.
Implementation Method 1
an optical current source 122 connected to the gate terminal 118
Implementation Method 2
a pulse transformer 120 connected to the gate terminal 118
Data Source
AI summary
A solid state switch includes a solid state device having an input terminal, an output terminal and a gate terminal; a quick response circuit selectively operable to initially place the solid state device in a conducting state; and a sustained response circuit selectively operable to maintain the solid state device in the conductive state after the quick response circuit. The input terminal and the output terminal are connected when the solid state device is in the conducting state and the input and the output terminal are disconnected when the solid state device is not in the conducting state.