ALD1123E/ALD1121E

Advanced Linear Devices

2

GENERAL DESCRIPTION

ALD1123E/ALD1121E are monolithic quad/dual EPAD® (Electrically Program-

mable Analog Device) N-channel MOSFETs with electrically adjustable threshold

(turn-on) voltage. The ALD1123E/ALD1121E are precision matched and adjusted

(e-trimmed) at the factory resulting in quad/dual MOSFETs that are highly matched

in electrical characteristics. The ALD1123E has four (4) separate source pins. SN1,

SN2 share a common substrate pin V-1 which has to be connected to the most

negative voltage potential. Likewise, SN3, SN4 share a common substrate pin V-2

which has to be connected to the negative voltage potential for SN3, SN4. The

ALD1121E has two (2) separate source pins (SN1, SN2). Both SN1, SN2 share a

common substrate pin 4 which has to be connected to the most negative voltage

potential.

Using an ALD1123E/ALD1121E MOSFET array is simple and straight forward. The

MOSFETs function in electrical characteristics as n-channel MOSFETs except that

all the devices have exceptional matching to each other. For a given input voltage,

the threshold voltage of a MOSFET device determines its drain on-current, resulting

in an on-resistance characteristic that can be precisely preset and then controlled

by the input voltage very accurately. Since these devices are on the same monolithic

chip, they also exhibit excellent tempco matching characteristics.

These MOSFET devices have very low input currents, and as a result a very high

input impedance (>10 12 Ohm). The gate voltage from a control source can drive

many MOSFET inputs with practically no loading effects. Used in precision current

mirror or current multiplier applications, they can be used to provide a current source

over a 100 nA to 3 mA range, and with either a positive, negative or zero tempco.

Optional EPAD Threshold Voltage Trimming By User

The basic EPAD MOSFET device is a monotonically adjustable device which means

the device can normally be e-trimmed to increase in threshold voltage and to

decrease in drain-on current as a function of a given input bias voltage. Used as an

in-circuit element for trimming or setting a combination of voltage and/or current

characteristics, it can be e-trimmed remotely and automatically. Once e-trimmed,

the set voltage and current levels are stored indefinitely inside the device as a

nonvolatile stored charge, which is not affected during normal operation of the

device, even when power is turned off. A given EPAD device can be adjusted many

times to continually increase its threshold voltage. A pair of EPAD devices can also

be connected differentially such that one device is used to adjust a parameter in one

direction and the other device is used to adjust the same parameter in the other

direction.

The ALD1123E/ALD1121E can be e-trimmed with the ALD EPAD programmer to

obtain the desired voltage and current levels. Or they can be e-trimmed as an active

in-system element in a user system, via user designed interface circuitry. PN1, PN2,

etc., are pins required for optional e-trim of respective MOSFET devices. If unused,

these pins are to be connected to V- or ground. For more information, see

Application Note AN1108.

APPLICATIONS

inaccessible nodes

and current mirrors

sources

shifter

current bias circuits

circuits

BLOCK DIAGRAM

BLOCK DIAGRAM

ALD1121E

ALD1123E

M 1

M 2

V- (4)

M 1

M 2

M 3

M 4