ALD114804/ALD114804A/ALD114904/ALD114904A Advanced Linear Devices 3 of 11
PERFORMANCE CHARACTERISTICS OF EPAD®
PRECISION MATCHED PAIR MOSFET FAMILY
ALD1108xx/ALD1109xx/ALD1148xx/ALD1149xx are monolithic
quad/dual N-Channel MOSFETs matched at the factory using ALD’s
proven EPAD® CMOS technology. These devices are intended for
low voltage, small signal applications.
ALD’s Electrically Programmable Analog Device (EPAD) technol-
ogy provides the industry’s only family of matched transistors with
a range of precision threshold values. All members of this family
are designed and actively programmed for exceptional matching of
device electrical characteristics. Threshold values range from -
3.50V Depletion to +3.50V Enhancement devices, including stan-
dard products specified at -3.50V, -1.30V, -0.40V, +0.00V, +0.20V,
+0.40V, +0.80V, +1.40V, and +3.30V. ALD can also provide any
customer desired value between -3.50V and +3.50V. For all these
devices, even the depletion and zero threshold transistors, ALD
EPAD technology enables the same well controlled turn-off, sub-
threshold, and low leakage characteristics as standard enhance-
ment mode MOSFETs. With the design and active programming,
even units from different batches and different date of manufacture
have well matched characteristics. As these devices are on the
same monolithic chip, they also exhibit excellent tempco tracking.
This EPAD MOSFET Array product family (EPAD MOSFET) is avail-
able in the three separate categories, each providing a distinctly
different set of electrical specifications and characteristics. The first
category is the ALD110800/ALD110900 Zero-Threshold
™ mode
EPAD MOSFETs. The second category is the ALD1108xx/
ALD1109xx enhancement mode EPAD MOSFETs. The third cat-
egory is the ALD1148xx/ALD1149xx depletion mode EPAD
MOSFETs. (The suffix “xx” denotes threshold voltage in 0.1 V steps,
for example, xx=08 denotes 0.80V).
The ALD110800/ALD110900 (quad/dual) are EPAD MOSFETs in
which the individual threshold voltage of each MOSFET is fixed at
zero. The threshold voltage is defined as I
DS
= 1uA @ V
DS
= 0.1V
when the gate voltage V
GS
= 0.00V. Zero threshold devices oper-
ate in the enhancement region when operated above threshold volt-
age and current level (V
GS
> 0.00V and I
DS
> 1uA) and subthresh-
old region when operated at or below threshold voltage and cur-
rent level (V
GS
<= 0.00V and I
DS
< 1uA). This device, along with
other very low threshold voltage members of the product family,
constitute a class of EPAD MOSFETs that enable ultra low supply
voltage operation and nanopower type of circuit designs, applicable
in either analog or digital circuits.
The ALD1108xx/ALD1109xx (quad/dual) product family features
precision matched enhancement mode EPAD MOSFET devices,
which require a positive bias voltage to turn on. Precision threshold
values such as +1.40V, +0.80V, +0.20V are offered. No conductive
channel exists between the source and drain at zero applied gate
voltage for these devices, except that the +0.20V version has a
subthreshold current at about 20nA.
The ALD1148xx/ALD1149xx (quad/dual) features depletion mode
EPAD MOSFETs, which are normally-on devices when the gate
bias voltage is at zero volt. The depletion mode threshold voltage
is at a negative voltage level at which the EPAD MOSFET turns off.
Without a supply voltage and/or with V
GS
= 0.0V the EPAD
MOSFET device is already turned on and exhibits a defined and
controlled on-resistance between the source and drain terminals.
The ALD1148xx/ALD1149xx depletion mode EPAD MOSFETs are
different from most other types of depletion mode MOSFETs and
certain types of JFETs in that they do not exhibit high gate leakage
currents and channel/junction leakage currents. When negative
signal voltages are applied to the gate terminal, the designer/user
can depend on the EPAD MOSFET device to be controlled, modu-
lated and turned off precisely. The device can be modulated and
turned-off under the control of the gate voltage in the same manner
as the enhancement mode EPAD MOSFET and the same device
equations apply.
EPAD MOSFETs are ideal for minimum offset voltage and differen-
tial thermal response, and they are used for switching and amplify-
ing applications in low voltage (1V to 10V or +/-0.5V to +/-5V) or
ultra low voltage (less than 1V or +/- 0.5V) systems. They feature
low input bias current (less than 30pA max.), ultra low power
(microWatt) or Nanopower (power measured in nanoWatt) opera-
tion, low input capacitance and fast switching speed. These de-
vices can be used where a combination of these characteristics
are desired.
KEY APPLICATION ENVIRONMENT
EPAD( MOSFET Array products are for circuit applications in one
or more of the following operating environments:
* Low voltage: 1V to 10V or +/- 0.5V to +/- 5V
* Ultra low voltage: less than 1V or +/- 0.5V
* Low power: voltage x current = power measured in microwatt
* Nanopower: voltage x current = power measured in nanowatt
* Precision matching and tracking of two or more MOSFETs
ELECTRICAL CHARACTERISTICS
The turn-on and turn-off electrical characteristics of the EPAD
MOSFET products are shown in the Drain-Source On Current vs
Drain-Source On Voltage and Drain-Source On Current vs Gate-
Source Voltage graphs. Each graph show the Drain-Source On
Current versus Drain-Source On Voltage characteristics as a func-
tion of Gate-Source voltage in a different operating region under
different bias conditions. As the threshold voltage is tightly speci-
fied, the Drain-Source On Current at a given gate input voltage is
better controlled and more predictable when compared to many
other types of MOSFETs.
EPAD MOSFETs behave similarly to a standard MOSFET, there-
fore classic equations for a n-channel MOSFET applies to EPAD
MOSFET as well. The Drain current in the linear region (V
DS
<
V
GS
- V
GS(th)
) is given by:
I
D
= u . C
OX
. W/L . [V
GS
- V
GS(th)
- V
DS
/2] . V
DS
where: u = Mobility
C
OX
= Capacitance / unit area of Gate electrode
V
GS
= Gate to Source voltage
V
GS(th)
= Turn-on threshold voltage
V
DS
= Drain to Source voltage
W = Channel width
L = Channel length
In this region of operation the I
DS
value is proportional to V
DS
value
and the device can be used as gate-voltage controlled resistor.
For higher values of V
DS
where V
DS
>= V
GS
- V
GS(th)
, the satura-
tion current I
DS
is now given by (approx.):
I
DS
= u . C
OX
. W/L . [V
GS
- V
GS(th)
]
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