Tuning capacitance to enhance FET stack voltage withstand
First Claim
1. A stacked transistor RF switch apparatus, comprising:
- a transistor stack including a plurality of constituent transistors all coupled in series connection drain to source to form a series string for which internal nodes are those between adjacent transistors; and
at least one discrete physical capacitor element Ccomp coupled between an internal node and a parasitic drain capacitance of the series string of the stack, Ccomp having an impedance that is predominantly capacitive at primary frequencies of signals ordinarily controlled by the RF switch apparatus.
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Accused Products
Abstract
An RF switch to controllably withstand an applied RF voltage Vsw, or a method of fabricating such a switch, which includes a string of series-connected constituent FETs with a node of the string between each pair of adjacent FETs. The method includes controlling capacitances between different nodes of the string to effectively tune the string capacitively, which will reduce the variance in the RF switch voltage distributed across each constituent FET, thereby enhancing switch breakdown voltage. Capacitances are controlled, for example, by disposing capacitive features between nodes of the string, and/or by varying design parameters of different constituent FETs. For each node, a sum of products of each significant capacitor by a proportion of Vsw appearing across it may be controlled to approximately zero.
35 Citations
19 Claims
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1. A stacked transistor RF switch apparatus, comprising:
- a transistor stack including a plurality of constituent transistors all coupled in series connection drain to source to form a series string for which internal nodes are those between adjacent transistors; and
at least one discrete physical capacitor element Ccomp coupled between an internal node and a parasitic drain capacitance of the series string of the stack, Ccomp having an impedance that is predominantly capacitive at primary frequencies of signals ordinarily controlled by the RF switch apparatus. - View Dependent Claims (2, 3, 4)
- a transistor stack including a plurality of constituent transistors all coupled in series connection drain to source to form a series string for which internal nodes are those between adjacent transistors; and
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5. A stacked transistor RF switch apparatus, comprising:
- a transistor stack including a plurality of constituent transistors all coupled in series connection drain to source to form a series string for which internal nodes are those between adjacent transistors, each constituent transistor having an intrinsic drain-source capacitance proportional to a transistor size of each constituent transistor and a total effective drain-source capacitance Cds comprising the intrinsic drain-source capacitance and additional capacitance, wherein the transistor size of each constituent transistor is fabricated to provide a provide a different Cds value for at least two constituent transistors.
- View Dependent Claims (6, 7, 8, 9, 10, 11, 12)
- 13. A method of fabricating a stacked RF switch that includes a plurality of series connected constituent transistors in a series string for which internal nodes are those between each pair of adjacent transistors, wherein each constituent transistor has an intrinsic drain-source capacitance proportional to a transistor size of each constituent transistor and a total effective drain-source capacitance value Cds comprising the intrinsic drain-source capacitance and additional capacitance, the method comprising fabricating each constituent transistor with a transistor size such that the Cds values for at least two constituent transistors are different.
Specification