The present invention relates generally to analog switches and, more particularly, to an isolating switch that isolates nodes between two circuits when one or both of the nodes have unknown, unpredictable or varying potentials.
When a Field Effect Transistor (FET) is in a non-conductive state it should not allow any current to flow between its drain and source terminals. However, in practice sub-threshold currents (leakage currents) may flow between the drain and source terminals even when the transistor has a gate to source voltage that biases the transistor to a non-conductive state. Consequently, FETs are not suitable for “ON” and “OFF” switching applications where small amounts of leakage current could cause malfunctioning or incorrect results, for instance, in sensitive instrumentation, tuning or monitoring circuits. Thus, it would be advantageous to have a circuit with a FET that prevents or reduces leakage currents.
The invention, together with objects and advantages thereof, may best be understood by reference to the following description of preferred embodiments together with the accompanying drawings in which:
The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention, and is not intended to represent the only forms in which the present invention may be practised. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the invention. In the drawings, like numerals are used to indicate like elements throughout. Furthermore, terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that module, circuit, device components, structures and method steps that comprises a list of elements or steps does not include only those elements but may include other elements or steps not expressly listed or inherent to such module, circuit, device components or steps. An element or step proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements or steps that comprises the element or step.
In one embodiment, the present invention provides a semiconductor isolating switch having a first node, a second node, and a switch control node. There are two series connected primary FETs, where a first one the primary FETs is coupled between the first node and an intermediate node, and a second one of the primary FETs is coupled between the intermediate node and the second node. A controllable pull-up FET is coupled in series to a controllable pull-down FET. The controllable pull-up FET is coupled between a power rail node and a common node and the controllable pull-down FET is coupled between the common node and a ground rail node. A leakage control transistor is coupled between the common node and the intermediate node. The primary FETs, the controllable pull-up FET, the controllable pull-down FET, and the leakage control transistor each have a respective gate electrode coupled to the switch control node.
In another embodiment, the present invention provides an analog switch that includes a first circuit with a first circuit interconnecting node, and a second circuit with a second circuit interconnecting node. The analog switch selectively connects the first circuit interconnecting node to the second circuit interconnecting node. The analog switch also includes a first node coupled to the first circuit interconnecting node and a second node coupled to the second circuit interconnecting node. There are two series connected primary FETs, where a first one the primary FETs is coupled between the first node and an intermediate node, and a second one of the primary FETs is coupled between the intermediate node and the second node. A controllable pull-up FET is coupled in series to a controllable pull-down FET. The controllable pull-up FET is coupled between a power rail node and a common node and the controllable pull-down FET is coupled between the common node and a ground rail node. A leakage control transistor is coupled between the common node and the intermediate node. The primary FETs, the controllable pull-up FET, the controllable pull-down FET and the leakage control transistor each have a respective gate electrode coupled to a switch control node.
In yet another embodiment, the present invention provides an analog switch comprising two complementary semiconductor isolating switches, where each of the isolating switches includes a first node, a second node, and a switch control node. There are two series connected primary FETs, where a first one the primary FETs is coupled between the first node and an intermediate node, and a second one of the primary FETs is coupled between the intermediate node and the second node. A controllable pull-up FET is coupled in series to a controllable pull-down FET. The controllable pull-up FET is coupled between a power rail node and a common node and the controllable pull-down FET is coupled between the common node and a ground rail node. A leakage control transistor is coupled between the common node and intermediate node. The primary FETs, the controllable pull-up FET, the controllable pull-down FET, and the leakage control transistor each have a respective gate electrode coupled to the switch control node. The first nodes of each of the isolating switches are coupled together and the second nodes of each of the isolating switches are coupled together. Further, the switch control nodes of each of the isolating switches are coupled together by way of an inverter and each of the transistors of a first one of the switches is complementary relative to a respective transistor of a second one of the switches.
Referring now to
A controllable pull-up FET 118 is coupled in series to a controllable pull-down FET 120. The controllable pull-up FET 118 is coupled between the power rail node 110 and a common node 122 and the controllable pull-down FET 120 is coupled between the common node 122 and the ground rail node 108.
The switch 100 also includes a leakage control transistor 124 coupled between the common node 122 and the intermediate node 116. Further, gate electrodes 126, 128 of the primary FETs 112, 114, gate electrodes 130, 132 of the controllable pull-up FET 118 and the controllable pull-down FET 120, and the gate electrode 134 of the leakage control transistor 124 are all coupled to the switch control node 106.
As shown, a source electrode of the first one the primary FETs 112 is coupled to the intermediate node 116 and a drain electrode of the second one of the primary FETs 114 is coupled to the intermediate node 116. In this particular embodiment, the primary FETs 112, 114 and the controllable pull-down FET 120 are N-type transistors, and the controllable pull-up FET 118 and the leakage control transistor 124 are both P-type transistors. Also, a source electrode of the leakage control transistor 124 is coupled to the common node 122 and a respective drain electrode of the controllable pull-up FET 118 and the controllable pull-down FET 120 are also coupled to the common node 122. As shown, the source electrode of the controllable pull-up FET 118 is coupled to the power rail node 110 and the source electrode of the controllable pull-down FET 120 is coupled to the ground rail node 108. This embodiment has the source electrode of the second one of the primary FETs 114 coupled to the second node 104, and a drain electrode of the first one of the FETs 112 coupled to the first node 102.
In operation, when a control signal at the switch control node 106 is at a ground potential (GND) the pull-up FET 118 and the leakage control transistor 124 couple the intermediate node 116 to a supply potential (VDD), thereby controlling the first one the primary FETs 112 to be in a non-conductive state. More specifically, the gate to source potential (Vgs) of the N-type transistor 112 is approximately GND-VDD, which alleviates or substantially eliminates sub-threshold leakage currents between the first and second nodes 102, 104. In contrast, when the control node 106 is at a supply potential (VDD), the pull-down FET 120 couples the common node 122 to ground (GND) and thus the leakage control transistor 124 is in an “OFF” or non-conductive state. The primary FETs 112, 114 can therefore operate in their conductive states without being affected by the other transistors 118, 120,124.
Referring now to
A controllable pull-up FET 218 is coupled in series to a controllable pull-down FET 220. The controllable pull-up FET 218 is coupled between the power rail node 210 and a common node 222 and the controllable pull-down FET 220 is coupled between the common node 222 and the ground rail node 208.
The switch 200 also includes a leakage control transistor 224 coupled between the common node 222 and intermediate node 216. The gate electrodes 226, 228 of the primary FETs 212, 214, gate electrodes 230, 232 of the controllable pull-up FET 218 and controllable pull-down FET 220, and the gate electrode 234 of the leakage control transistor 224 are all coupled to the switch control node 206.
As shown, a source electrode of the first one the primary FETs 212 is coupled to the intermediate node 216 and a drain electrode of the second one of the primary FETs 214 are coupled to the intermediate node 216. In this particular embodiment the primary FETs 212, 214 and the controllable pull-up FET 218 are P-type transistors, and the controllable pull-down FET 220 and leakage control transistor 224 are both N-type transistors. Also, a source electrode of the leakage control transistor 224 is coupled to the common node 222 and a respective drain electrode of the controllable pull-up FET 218 and the controllable pull-down FET 220 are also coupled to the common node 222. As shown, the source electrode of the controllable pull-up FET 218 is coupled to the power rail node 210 and the source electrode of the controllable pull-down FET 220 is coupled to the ground rail node 208. This embodiment also shows the source electrode of the second one of the primary FETs 214 being coupled to the second node 204, and a drain electrode of the first one of the FETs 212 being coupled to the first node 202.
In operation, when a control signal at the switch control node 206 is at a supply potential (VDD) the pull-down FET 220 and leakage control transistor 224 couple the intermediate node 216 to a ground potential (GND) thereby controlling the first one the primary FETs 212 to be in a non-conductive state. More specifically, the gate to source potential (Vgs) of P-type transistor 212 is approximately VDD-GND thus alleviating or substantially eliminating sub threshold leakage currents between first and second nodes 202, 204. In contrast, when the control node 206 is at a ground potential (GND) the pull-up FET 218 couples the common node 222 to the supply potential (VDD) and thus the leakage control transistor 224 is in an “OFF” or non-conductive state. The primary FETs 212, 214 can therefore function in their conductive states without being affected by the other transistors 218, 220, 224.
Referring now to
Each of the transistors of a first one of the semiconductor isolating switches is complementary relative to each respective transistor of a second one of the semiconductor isolating switches. More specifically, in this embodiment the two series connected primary FETs 112, 114, the controllable pull-down FET 120 of the first one of the switches 100 are N-type transistors, whereas the controllable pull-up FET 118 and the leakage control transistor 124 of the first one of the switches 100 are P-type transistors. In contrast, the two series connected primary FETs 212, 214, the controllable pull-up FET 218 of the second one of the switches 200 are P-type transistors, whereas the controllable pull-down FET 220 and leakage control transistor 224 of the second one of the switches 200 are N-type transistors.
There is also a second circuit 510 with a second circuit interconnecting node 512. Again, by way of example, the second circuit 510 is formed from a third capacitor C3 across the second circuit interconnecting node 512 and the analog circuit node 504, and a series connected resistor R2 and a capacitor C4 also are coupled across the second circuit interconnecting node 512 and the analog circuit node 304. In this embodiment the second circuit interconnecting node 512 is a common node of the series connected resistor R2 and third Capacitor C3.
The analog circuit 500 provides selective connecting of the first circuit interconnecting node 508 to the second circuit interconnecting node 512. In this regard, the first node 502 is coupled to the first circuit interconnecting node 508 and the second node 504 is coupled to the second circuit interconnecting node 512. However, it will be appreciated that the analog circuit 500 can be replaced, for instance, with the semiconductor switch 200 or with either of the semiconductor isolating circuits 300, 400.
Advantageously, the present invention reduces leakage currents in semiconductor switches and is especially useful, but not necessarily limited to, reducing such leakage currents in analogue circuit applications.
The description of the preferred embodiments of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or to limit the invention to the forms disclosed. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiment disclosed, but covers modifications within the spirit and scope of the present invention as defined by the appended claims.
Number | Date | Country | Kind |
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201410408825.7 | Jun 2014 | CN | national |