Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Parameter related to the reproduction or fidelity of a...
Reexamination Certificate
2000-09-28
2004-02-17
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Parameter related to the reproduction or fidelity of a...
C324S612000
Reexamination Certificate
active
06693439
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to apparatus and methods for measuring noise in a device. In particular, this invention relates to apparatus and methods for measuring noise in a transistor device.
BACKGROUND OF THE INVENTION
Circuit designers typically use design tools to design integrated circuits. The most common design tools are the so-called simulated-program-with-integrated-circuit-emphasis (SPICE) and the fast device level simulators (e.g., Star-Sim, ATS, MACH TA, and TIMEMILL). Typically, design tools, such as SPICE and fast device level simulators, describe individual device and its connections in a line-by-line manner. Examples of individual devices are resistor, capacitor, inductor, bipolar junction transistor, and metal oxide semiconductor field effect transistor (MOSFET). In a design tool, each line, which includes a description of a device, is sometimes referred to as a device specification instance.
FIG. 1A
illustrates an exemplary netlist developed by a design tool, such as SPICE. As shown in
FIG. 1A
, a netlist
101
typically includes three sections: a circuit description section
103
, a models section
105
, and an analysis section
107
. The circuit description section
103
contains a description of each device and sub-circuit as well as interconnections between the devices and sub-circuits within an integrated circuit. The models section
105
contains a description of individual device and sub-circuit behavior. Typically, the models section
105
comprises a library of model parameters, model parameter values, and model equations. Generally, the behavior of each type of device (e.g., a MOSFET) can be simulated by at least one model equation, which includes a combination of model parameters. The analysis section
107
typically includes analysis instructions to simulate a device, sub-circuit, or circuit (e.g., output voltage over time) using information in the circuit description section
103
and the models section
105
.
In order to meet continuous demands to reduce manufacturing costs and device size, many manufacturers have begun to manufacture chips that contain all components of an integrated circuit. Although less expensive to manufacture, such chips are more expensive to design. One important design factor is to measure and account for device and chip noise. Noise is a phenomenon that exists in analog or digital devices in an integrated circuit. Typically, noise is inversely proportional to device size. That is, as device size decreases, noise increases. Thus, as the industry continues to reduce device size, it is increasingly important to be able to measure and account for noise during integrated circuit design.
In most existing noise measurement systems, three components are present: a biasing system for biasing a device under test (DUT), a noise amplifier for amplifying noise measured from the DUT, and a control unit for controlling the biasing system and the amplifier. An efficient noise measuring system requires that the noise measuring system itself does not generate noise that interferes with or engulfs the noise measured from the DUT.
In some existing biasing systems, batteries are used to bias a DUT. Batteries are pure chemical power sources, thus, are relatively noiseless. One drawback of using batteries as a power source is that the voltage provided by a battery is typically not adjustable. Some biasing systems use a potential meter to adjust battery voltage. However, a potential meter generally produces unwanted thermal noise when used. In other existing biasing systems, an electronic circuit is connected to a battery to adjust battery voltage. Using such electronic circuit, for example a digital-to-analog converter, is preferable over using a potential meter because the electronic circuit is generally quieter. However, designing an effective and quiet electronic circuit can be very expensive; thus, this solution is not widely adopted. In yet other existing biasing systems, a commercial programmable DC power supply is used. Such commercial DC power supply can be programmed to provide adjustable biasing voltages. A drawback of the commercial DC power supply is that the power supply itself generates noise.
In most noise measurement systems, a noise amplifier is used to amplify a weak DUT noise to a measurable level. To be effective, the amplifier should generate minimal noise and that amplifier noise should be distinguishable from the measured DUT noise. Further, ideally, the noise amplifier should be capable of amplifying a wide range of noise frequencies (e.g., between 0 Hz and 1 MHz). Generally, an amplifier has its own input impedance. Amplifier performance generally improves if the amplifier impedance is closely matched by the impedance of the DUT. In most existing amplifiers, the amplifier impedance is generally fixed or very difficult to adjust. Thus, to achieve impedance matching, the DUT impedance should be adjustable to match the amplifier impedance.
Thus, it is desirable to provide apparatus and methods for effectively measuring noise in a device such as a transistor device.
SUMMARY OF THE INVENTION
An exemplary apparatus for measuring noise in a device comprises a plurality of programmable power supply units, a plurality of filter circuits coupled to the power supply units and selective terminals of a device, a variable loading resistor circuit coupled to a first terminal of the device, a calibration circuit coupled to a second terminal of the device, an amplifier circuit coupled to the first terminal of the device, and an output analyzer coupled to the amplifier circuit. The calibration circuit calibrates a gain of both the device and the amplifier circuit under each bias condition. In one embodiment, each of the plurality of filter circuits comprises a variable resistor and a capacitor coupled to the variable resistor. In another embodiment, the variable loading resistor circuit comprises a plurality of resistors selectably coupled in parallel, such that each resistor of the plurality of resistors can be turned on via a switch individually or in combination with other resistors of the plurality of resistors. In yet another embodiment, the variable loading resistor circuit further comprises a switch for shorting the variable loading resistor circuit.
In an exemplary embodiment of the apparatus, the amplifier circuit comprises a first phase amplifier circuit and a second phase amplifier circuit. In one embodiment, the first phase amplifier circuit includes a switch assembly. The switch assembly switchable coupling a voltage amplifier, a current amplifier, or a short circuit based on the impedance of the device. In another embodiment, the first phase amplifier circuit is configured to operate in a voltage amplifier mode or a current amplifier mode based on the impedance of the device. The second phase amplifier circuit further amplifies signals received from the first phase amplifier circuit.
In another exemplary embodiment, the apparatus further includes a protection circuit for discharging accumulated charge. The protection circuit is switchable coupled to the second terminal of the device. In yet another exemplary embodiment, the apparatus further includes a variable input resistor that is switchable coupled between the second terminal of the device and a filter circuit. In one embodiment, the variable input resistor is connected when the device is a bipolar transistor or a deep submicron device.
An exemplary method for measuring noise in a device comprises receiving a bias condition, measuring direct current operating points based on said bias condition, determining a loading resistor value based on a device impedance and an amplifier impedance, calculating a supply voltage based on the direct current operating points and the loading resistor value, selecting an amplifier mode based on the device impedance, calibrating a device gain and an amplifier gain, measuring noise data under the bias condition, removing an undesired portion of the noise data to obtain device noise data, extracting a model based on t
Hung Kwok Kwong
Liang Hancheng
Liu Zhihong
Benson Walter
Cadence Design Systems Inc.
Le N.
Pennie & Edmonds LLP
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