Method and apparatus for measuring the capacitance of complementary field-effect transistor devices
AssigneeTexas Instruments Incorporated
InventorsShivaling S. Mahant-Shetti, Aki Nishimura
Life of this patent
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Abstract
A combination inverter chain and ring oscillator (200) is used to measure the capacitance of a field effect transistor device (12, 85, 202) by measuring the current associated with propagating a signal through the circuit at a certain signal frequency. Where the device (12) is a CMOS pair, the capacitance thus obtained is reduced by a constant factor to take crowbar current (52) into account. Once the capacitance for a basic or reference device (84) has been determined, the basic structure may be modified to derive incremental per-unit area capacitances for various components of the device structure.
Claims27
Apparatus for measuring the capacitance inside a complementary field-effect transistor circuit, comprising:
- a plurality of first complementary field-effect transistor devices connected in series, said plurality of first devices including an input and an output;
- a signal source coupled to said input for providing a signal;
- a plurality of second complementary field-effect transistor devices, including an input and an output, connected in series, each differing from said first field-effect transistor devices in that each second device is connected to at least one additional load element;
- a supply voltage source connected to said devices, said supply voltage enabling said devices to propagate said signal;
- a meter for measuring a current required to propagate said signal through said devices from said input to said output;
- a first capacitance of said transistor circuit derived from a measurement of a current drawn by said plurality of first transistor devices in propagating a signal therethrough;
- and
- a second capacitance of said circuit derived from a current drawn by said plurality of second devices in propagating a signal therethrough, the contribution of said additional element to said second device capacitance calculated by using the first capacitance and the second capacitance.
A method for measuring capacitances inside a complementary field effect transistor circuit comprising:
- exciting a series of inverter chains with a signal of a predetermined frequency, each chain including both a series of complementary field effect transistor inverters and a set of loads, each load of a set being attached to an associated complementary field effect transistor inverter in its inverter chain;
- measuring the current through each inverter chain;
- adjusting the measured current by a correction factor corresponding to a crowbar current;
- and
- calculating the capacitive load at each inverter chain from the values of the adjusted measured current and the predetermined frequency.
An apparatus for measuring capacitances inside a complementary field effect transistor circuit comprising:
- a series of inverter chains, each chain including an input and an output in addition to a series of complementary field effect transistor inverters and a set of loads, each load of a set being attached to an associated complementary field effect transistor inverter in its inverter chain, the inverter chain series further including one inverter chain wherein each load from its set of loads is of a first predetermined value and wherein the values of the loads from the set of loads of the remaining complementary field effect transistor inverter chains are incrementally above the first predetermined value;
- a signal source means, coupled to the chain inputs, for providing a signal of a predetermined frequency;
- a supply voltage means, connected to the inverter chains, for enabling the chains to propagate the signal;
- and
- a meter means, connected to the chains' outputs, for measuring a current required to propagate the signals through the chains whereby capacitances within the chains are calculated based on the signal frequency and relative values of measured current in the chains.
A method for measuring capacitances inside a complementary field effect transistor circuit comprising:
- exciting a series of inverter chains with a signal, each chain including both a series of complementary field effect transistor inverters and a set of loads, each load of a set being attached to an associated complementary field effect transistor inverter in its inverter chain;
- measuring the frequency of the signal;
- measuring the current through each inverter;
- adjusting the measured current by a correction factor corresponding to a crowbar current;
- and
- calculating the capacitive load at each inverter chain from the values of the adjusted measured current and the predetermined frequency.
Dependencies are inferred from the claim text.