PERFORMANCE CHARACTERISTICS OF EPAD
®
PRECISION MATCHED PAIR MOSFET ARRAY FAMILY
ALD2108xx/ALD2148xx/ALD2129xx/ALD2169xx high precision
monolithic quad/dual N-Channel MOSFET arrays are enhanced
versions of the ALD1108xx/ALD1109xx EPAD
®
MOSFET family, with
increased forward transconductance and output conductance, in-
tended for operation at very low power supply voltages. These de-
vices are also capable of sub-threshold operation with <1nA of op-
erating supply currents and at the same time delivering higher out-
put drive currents (typ. >50mA). They feature precision Gate Off-
set Voltages, V
OS
, defined as the difference in V
GS(th)
between
MOSFET pairs M1 and M2 or M3 and M4.
ALD's Electrically Programmable Analog Device (EPAD
®
) technol-
ogy provides the industry's only family of matched MOSFET tran-
sistors with a range of precision gate-threshold voltage values. All
members of this family are designed and actively programmed for
exceptional matching of device electrical and temperature charac-
teristics. Gate Threshold Voltage V
GS(th)
values range from -3.50V
Depletion Mode to +3.50V Enhancement Mode devices, including
standard products with V
GS(th)
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 V
GS(th)
between -3.50V and
+3.50V on a special order basis. For all these devices ALD EPAD
technology enables excellent well-controlled gate threshold volt-
age, subthreshold voltage, and low leakage characteristics. With
well matched design and precision programming, units from differ-
ent production lots provide the user with exceptional matching and
uniformity characteristics. Built on the same monolithic IC chip, the
units also have excellent temperature tracking characteristics.
This ALD2108xx/ALD2148xx/ALD2129xx/ALD2169xx EPAD
MOSFET Array product family (EPAD MOSFET) is available in three
separate categories, each providing a distinctly different set of elec-
trical specifications and characteristics. The first category is the
ALD210800A/ALD210800/ALD212900A/ALD212900 Zero-Thresh-
old™ mode EPAD MOSFETs. The second is the ALD2108xx/
ALD2129xx enhancement mode EPAD MOSFETs. The third cat-
egory includes the ALD2148xx/ALD2169xx depletion mode EPAD
MOSFETs. (The suffix “xx” denotes threshold voltage in 0.1V steps,
for example, xx=08 denotes 0.80V). For each device, there is a
zero-tempco bias current and bias voltage point. When a design
utilizes such a feature, then the gate-threshold voltage is tempera-
ture stable, greatly simplifying certain designs where stability of
certain circuit parameters over a temperature range is desired.
ALD210800A/ALD210800 (quad) and ALD212900A/ALD212900
(dual) EPAD MOSFETs are Zero Threshold MOSFET transistors in
which the individual gate-threshold voltage of each MOSFET is set
at zero, defined as V
GS(th)
= 0.00V at I
DS(ON)
= 10µA @ V
DS(ON)
= +0.1V. Zero Threshold MOSFETs operate in the enhancement
region when operated above threshold voltage (V
GS
> 0.00V and
I
DS
> 10µA) and subthreshold region when operated at or below
threshold voltage (V
GS
<= 0.00V and IDS < 10µA). These devices,
along with other low V
GS(th)
members of the product family, enable
ultra low supply voltage analog or digital operation and nanopower
circuit designs, thereby reducing or eliminating the use of very high
valued (expensive) resistors in many cases.
The ALD2108xx/ALD2129xx (quad/dual) product family features
precision matched enhancement mode EPAD MOSFET devices,
which require a positive gate bias voltage V
GS
to turn on. Precision
V
GS(th)
values at +3.30V, +1.40V, +0.80V, +0.40V and +0.20V are
offered. No conductive channel exists between the source and drain
at zero applied gate voltage (VGS = 0.00V) for +3.30V, +1.40V and
+0.80V versions. The +0.40V and the +0.20V versions have a sub-
threshold current at about 1nA and 100nA for the ALD2108xx (2nA
and 200nA for the ALD2129xx) respectively at zero applied gate
voltage. They are also capable of delivering lower R
DS(ON)
and
higher output currents greater than 68mA (see specifications).
ALD210800/ALD210800A
The ALD2148xx/ALD2169xx (quad/dual) features Depletion Mode
EPAD MOSFETs, which are normally-on devices at zero applied
gate voltage. The V
GS(th)
is set at a negative voltage level (V
GS
<
V
S
and V
GS
>V-) at which the EPAD MOSFET turns off. Without a
supply voltage and/or with V
GS
= V- = 0.00V = Ground, the EPAD
MOSFET device is already turned on and exhibits a defined and
controlled on-resistance R
DS(ON)
. An EPAD MOSFET may be
turned off when a negative voltage is applied to V- pin and V
GS
set
more negative than its V
GS(th)
. These Depletion Mode EPAD
MOSFETs are different from most other depletion mode MOSFETs
and JFETs in that they do not exhibit high gate leakage currents
and channel/junction leakage currents, while they stay controlled,
modulated and turned off at precise voltages. The same MOSFET
device equations as those for enhancement mode devices apply.
KEY APPLICATION ENVIRONMENTS
EPAD MOSFETs are ideal for circuits requiring low V
OS
and low
operating currents with tracked differential thermal responses. They
feature low input bias currents (less than 200pA max.), low input
capacitance and fast switching speed. These and other operating
characteristics offer unique solutions in one or more of the follow-
ing operating environments:
* Low supply voltage: 0.1V to 10V or +0.05V to +5V
* Ultra low supply voltage: less than +10mV to +0.1V
* Nanopower operation: voltage x current = nW or uW
* Precision V
OS
characteristics
* Matching and tracking of multiple MOSFETs
* Matching across multiple packages
ELECTRICAL CHARACTERISTICS
The turn-on and turn-off electrical characteristics of the EPAD
MOSFET products are shown in the I
DS(ON)
vs. V
DS(ON)
and
I
DS(ON)
vs. V
GS
graphs. Each graph shows I
DS(ON)
versus V
DS(ON)
characteristics as a function of V
GS
in a different operating region
under different bias conditions, while I
DS(ON)
at a given gate input
voltage is controlled and predictable. A series of four graphs titled
“Forward Transfer Characteristics”, with the second and third sub-
titled “expanded (subthreshold)” and “further expanded (subthresh-
old)”, and the fourth sub-titled “low voltage”, illustrates the wide
dynamic operating range of these devices.
Classic MOSFET equations for an N-channel MOSFET also apply
to EPAD MOSFETs. The drain current in the linear region (V
DS(ON)
< V
GS
- V
GS(th)
) is given by:
I
DS(ON)
= u . C
OX
. W/L . [V
GS
- V
GS(th)
- V
DS
/2] . V
DS(ON)
where:
u = Mobility
C
OX
= Capacitance / unit area of Gate electrode
V
GS
= Gate to Source Voltage
V
GS(th)
= Gate Threshold (Turn-on)Voltage
V
DS(ON)
= Drain to Source On Voltage
W = Channel width
L = Channel length
In this region of operation the I
DS(ON)
value is proportional to the
V
DS(ON)
value and the device can be used as a gate-voltage con-
trolled resistor.
For higher values of V
DS(ON)
where V
DS(ON)
>= V
GS
- V
GS(th)
,
the saturation current I
DS(ON)
is now given by (approx.):
IDS(ON)
= u . C
OX
. W/L . [V
GS
- V
GS(th)
]
2
Advanced Linear Devices
3 of 12
ALD [ ADVANCED LINEAR DEVICES ]
