ETC 233

Model 233 is a low cost. low offset, chopper stabilized on. Use of
integrated circuits and advanced technology have made it possible to
effect a major price reduction for chopper stabilization. Size is reduced
to 1.5" X 1.5" X 0.4".
Model 233
With its record low cost, the Model 233 now makes feasible
incorporation of chopper stabilization in applications where cost was
previously prohibitive. Users of other chopper stabilized amplifiers can
effect both a profit increase, and a price reduction in their marketplace,
by using the low-cost Model 233. Other advantages of the Model 233
over non-chopper stabilized systems include elimination of offset
voltage adjustments in many applications and the superb long term
stability of the chopper stabilized circuit. Even manufacturers who have
made their own op amps "in-house" will find that the Model 233 allows
them to free up their engineering and manufacturing talent for work
more directly associated with their end item products.
Low Drift, to 0.1µV/°C max
to 0.5pA/°C max
Low Offset, to 20µV max
Low Noise, 1µV p-P
0.01 -1 Hz
One of the prime advantages of the chopper-stabilized system over
other low drift amplifiers is long term stability. While non-chopper
stabilized systems can achieve 0.25µV/°C offset voltage, the offset drift
with time of a chopper stabilized system will be less. The Model 233’s
long term drift is 2µV/month. It is important to remember that long
term drifts do not accumulate linearly. Experience has shown that the
increase in long term drift will be approximately the square root of the
time factor increase multiplied by the basic drift coefficient. For
example, with a long term drift of 2µV/month, the yearly drift would be
only 7µV.
The initial offset voltage of the Model 233J is 50µV, and only 20µV for
the Models 233K and 233L. In many applications the use of the Model
233, as compared to non-stabilized amplifiers, will be justified simply
by the elimination of the offset potentiometer and the cost of making
this adjustment on the production line. Some users now providing front
panel zero adjustments on their equipment will be able to eliminate this
control, its associated costs, and sell a superior product.
Of prime importance in a low drift amplifier are low current and
voltage noise. Good noise performance is mandatory if one is to be able
to resolve the small signals that low drift amplifiers of this variety are
normally called upon to amplify. In the Model 233, voltage noise has
been reduced to lµV p-p (0.01-lHz), and current noise is 3pA p-p in the
same bandwidth. For 0.1-l0Hz, the corresponding figures are 3µV p-p
and 6pA p-p. These low values of noise make it possible to accurately
amplify small signals and improve the design’s overall signal to noise
ratio. In particular, the low level of current noise makes it possible to
use the Model 233 with moderately high (e.g. 500kΩ) input resistance
without significantly degrading the overall noise performance.
Model 233 is designed for inverting operation, although it can be used
as a non-inverting amplifier when combined with a floating power
supply. For most low frequency non-inverting applications Model 260
non-inverting chopper amplifier is an excellent choice.
Precision Amplification
Current & Voltage Summation
Reference Buffering
Controlled Current Source
Bridge Amplifier
1400 Providence Highway, Building #2
Norwood, MA 02062
Phone (781) 551-5500
FAX (781) 551-5555