Frequently Asked Questions About EPAD MOSFET
   
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1. What exactly is an EPAD MOSFET?
EPAD MOSFET stands for "Electrically Programmable Analog Device matched Pair MOSFET Array". EPAD is an analog technology innovation by ALD in which a unique CMOS MOSFET whose threshold voltage and on-resistance characteristics can be electrically programmed to a precise level. Once programmed, the set parameters are indefinitely stored within the device even after power is removed. This technology employ a floating gate structure which can be precision trimmed to produce tightly controlled transistor electrical characteristics.

2. Where can I use an EPAD?
You can use an EPAD MOSFET as a regular MOSFET in almost any low voltage circuit application where precision is required to achieve the desired performance -- including precision threshold voltages, offset voltages, matching and temperature compensated applications. They can also be used where certain other features such as Nanopower™, ZeroThreshold™ and Depletion modes of operation are desired.

3. What are the intended applications for an EPAD MOSFET?
EPAD-based MOSFET devices are linear components that are intended for use in ATE, instrumentation and industrial control systems. They are also useful for portable telecom, medical instruments, miniaturized data terminals, data acquisition, and sensor interface applications.

4. Is EPAD MOSFET a cost-effective solution?
Depending on the application and volume, EPAD MOSFET can represent a very cost- effective alternative to other devices or methods. EPAD MOSFETs are cost-effective in terms of unit costs, up-front capital equipment costs and production labor costs. EPAD MOSFETs also offers important device performance characteristics unavailable elsewhere.

5. Can I use this device as a trimmer potentiometer substitute?
Yes, in general the device can be used as a functional trimmer pot substitute in conjunction with external fixed resistor(s). The primary function of an EPAD MOSFET is as a high precision, high stability MOSFET transistor that offers a unique family of voltage versus current characteristics. Originally, EPAD MOSFETs were used as a trimming function where the on-resistance of the MOSFET could be precisely set to replace a trimmer potentiometer. Recently many other uses have emerged, where EPAD MOSFETs are used for their unique MOSFET transistor capabilities that go far beyond a trimmer-pot function. An EPAD MOSFET is actually a CMOS I.C. circuit, and it has some general limitations of typical CMOS devices such as a maximum voltage rating of 10V. It is sensitive to ESD (electro-static discharge) and it has an NMOS MOSFET device output.

6. Do I have to learn how to program an EPAD?
No, the technology on EPAD MOSFETs has evolved to the point that most "programming" is performed at the factory and the user no longer has to be concerned with it. EPAD MOSFET is available now primarily as a factory-prepared, ready-to-use standard product. On a more custom basis, contact factory on field programming by user with one of several Programmer and different adapter modules for specific applications.

7. Do you have any application notes?
Yes, you can download a copy of Application Note AN1108. Also available is a White Paper entitled "New Design Concepts in Ultra Low Voltage and Nanopower™ Circuits with EPAD MOSFET Arrays". For additional technical data, please consult "Performance Characteristics of EPAD MOSFET Arrays".

8. What is a simple model of an EPAD MOSFET?
A simple model of an EPAD is simply that of a regular MOSFET device, with all the electrical characteristics as indicated on the datasheet. The floating gate can be just regarded as an embedded part of the EPAD MOSFET. An EPAD can be modeled as a MOSFET with a floating gate between the gate control terminal and the MOSFET device. This floating gate can receive tiny, controlled burst of electrons and trap them indefinitely.

9. How often can I program an EPAD MOSFET?
An EPAD MOSFET can be programmed a few times, provided that useful voltage adjustment range remains. However, the technology on EPAD MOSFETs has evolved to the point that most "programming" is performed at the factory and the user no longer has to be concerned with it. EPAD MOSFET is available now primarily as a factory-prepared, ready-to-use standard product. The guaranteed specifications of a standard product help reduce device complexities and ease the burden on the circuit designer.

10. Can I erase a programmed EPAD MOSFET?
No. A programmed EPAD MOSFET cannot be erased normally.

11. How reliable is an EPAD? What is the long term age and reliability?
Based on ALD engineering data accumulated over several years, an EPAD device is extremely reliable. Extrapolated data indicates that there is virtually no escape of these electrons from the floating gate. As a result, the total amount of electrons on the floating gate remains the same after 100 years. The extrapolated life of an EPAD is well over 100 years. However, care must be observed in its use as an improperly used or misused EPAD MOSFET can be damaged. Stressing the device beyond its ratings, ESD damage, and other forms of damage of the device can render the device to become inoperable.

12. What is the difference between the different modes of operation?
The primary difference lies in the intended user environment. There are numerous modes of circuit operation of these devices. A few of the different modes are:

13. N-Channel Zero Threshold Mode
The Zero Threshold MOSFET is an EPAD MOSFET Array where the individual threshold voltage of each MOSFET is fixed at zero. These devices are unique by using ALD EPAD technology to offer very low voltage switching with sharp turn-off and very low leakage characteristics similar to that for a conventional MOSFET. The zero threshold voltage is defined as IDS = 1µA @ VDS = 0.1V when the gate voltage VGS = 0.00V.

14. N-Channel Enhancement Mode
The ALD1108xx/ALD1109xx products are enhancement mode EPAD MOSFET devices, which require a positive bias voltage to turn on. Precision threshold values such as +1.50V, +0.80V, +0.40V and +0.20V are offered as standard products.

15. N-Channel Depletion Mode
ALD1148xx/ALD1149xx products are depletion mode EPAD MOSFETs, which are normally-on devices when the gate bias voltage is at 0.0V. The depletion mode threshold voltage is at a negative voltage at which the MOSFET device turns off. Negative threshold values such as -0.40V, -1.30V and -3.50V are offered.

16. Can I have a custom I.C. developed with an EPAD embedded?
Yes. EPADs are part of the ALD Function-Specific I.C. solution for high volume mixed analog/digital custom I.C. applications.

17. Who should I contact to get application assistance?
Call, fax or e-mail to: techsupport@aldinc.com
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