High-efficiency filler cell with switchable, integrated buffer capacitance for high frequency applications
A cell based integrated circuit chip includes a top voltage supply rail and a bottom voltage supply rail and a plurality of metal layers defining at least one filler cell. The filler cell is formed by a first field effect transistor of a first type conductivity, typically an n-channel MOSFET. The source or drain electrodes of the n-channel MOSFET are arranged to as act as a capacitor with respect to the bottom voltage supply rail and to which at least one of the source and drain electrodes is connected. A second field effect transistor of an opposite-type conductivity to the first field effect transistor, typically a p-channel MOSFET, is also provided. The source or drain electrodes of the p-channel MOSFET are connected in series between the top voltage supply rail and a gate electrode of the n-channel MOSFET. The gate electrode of the p-channel MOSFET is connected to a source of ground potential via a resistor.
1. An integrated circuit chip with a top voltage supply rail and a bottom voltage supply rail, the integrated circuit chip comprising: a plurality of metal layers defining at least one filler cell, wherein a first field effect transistor of a first type conductivity is provided with a source electrode and a drain electrode arranged so as to act as a capacitor with respect to the bottom voltage supply rail to which one of the source electrode or the drain electrode is connected; and a second field effect transistor of an opposite-type conductivity to the first field effect transistor provided with a source electrode or a drain electrode, connected in series between the top voltage supply rail and a gate electrode of the first field effect transistor and with the second field effect transistor gate electrode connected to a ground potential, wherein the source or drain electrode of the first field effect transistor that is not connected to the bottom voltage supply rail is in an unconnected state.
2. An integrated circuit chip as claimed in claim 1 , wherein the second field effect transistor gate electrode is grounded via a layer of non-silicided polysilicon.
3. An integrated circuit chip as claimed in claim 2 , wherein the second field effect transistor gate electrode is connected to a control signal.
4. An integrated circuit chip as claimed in claim 2 , wherein a first metal layer of the plurality of metal layers comprises an interconnect between the layer of non-silicided polysilicon and the bottom voltage supply rail.
5. An integrated circuit chip as claimed in claim 1 , wherein a first metal layer of the plurality of layers is used to form an interconnection between the first field effect transistor and the second field effect transistor.
6. An integrated circuit chip as claimed in claim 1 , wherein the first field effect transistor and the second field effect transistor comprise long channel MOSFETs.
7. A cell-based integrated circuit chip layout comprising a plurality of standard cells and a plurality of filler cells as defined in claim 1 , wherein any of the filler cells fits within pre-defined standard cell dimensions.
8. An integrated circuit chip as claimed in claim 1 , wherein neither of the source or drain electrodes of the first field effect transistor are coupled to the second field effect transistor.
9. An integrated circuit chip with a top voltage supply rail and a bottom voltage supply rail comprising: a plurality of metal layers defining at least one filler cell, wherein an n-channel MOSFET is provided with a source electrode and a drain electrode arranged to as act as a capacitor with respect to the bottom voltage supply rail to which one of the source electrode or the drain electrode is connected; and a p-channel MOSFET, provided with a source electrode or a drain electrode, connected in series between the top voltage supply rail and a gate electrode of the n-channel MOSFET and with the p-channel MOSFET gate electrode connected to a ground potential, wherein source or drain electrode of the n-channel MOSFET that is not connected to the bottom voltage supply rail is in an unconnected state.
10. An integrated circuit chip as claimed in claim 9 , wherein the p-channel MOSFET gate electrode is grounded via a layer of non-silicided polysilicon.
11. An integrated circuit chip as claimed in claim 9 , wherein the p-channel MOSFET gate electrode is grounded by connection to a control signal.
12. A cell-based integrated circuit chip layout comprising a plurality of standard cells and a plurality of filler cells as defined in claim 7 , wherein any of the filler cells fits within pre-defined standard cell dimensions.
13. An integrated circuit chip as claimed in claim 9 , wherein neither of the source or drain electrodes of the n-channel MOSFET are coupled to the p-channel MOSFET.