Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Particular stable state circuit
Reexamination Certificate
2000-10-31
2001-08-28
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Particular stable state circuit
C327S182000
Reexamination Certificate
active
06281732
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to bistable, monostable and astable multivibrators in which the switching transition level is stable and relatively independent of ambient temperature. Applications for stable multivibrator are in but not limited to the fields of analog to digital converters, pulse generators, and oscillators.
BACKGROUND ART
One of the problems associated with multivibrators is that the switching transition level is very sensitive to changes in ambient temperature and power supply voltage. This change causes the multivibrator to have variations in the pulse duration time or oscillation frequency. To reduce this instability some form of compensation is necessary. One of the methods used is to use a FET as a resister to control the charging time of a capacitor. The FET resistance value is controlled by a temperature dependent voltage, which varies to maintain a constant capacitor charging time. This is described in U.S. Pat. No. 4,547,749 issued to Clinton Kuo. Another method is to use a constant current source circuit, which is designed to be temperature independent, to charge and discharge a timing capacitor. This is described in U.S. Pat. No. 4,714,901 issued to Jain et al.
In these methods the variation in pulse duration time or oscillator frequency has been reduced by controlling the charging time of capacitors, but nothing has been done to correct an other large error source, the sensitivity of the amplifier input offset voltage to temperature and supply voltage change.
SUMMARY OF THE INVENTION
The object of this invention are bistable, monostable and astable multivibrators in which the pulse duration or frequency stability, respectively is increased by reducing the change in the amplifier input offset voltage due to variations in operating temperature, power supply voltage and component parameter variations. This maintains a stable switching transition level. This reduction is accomplished by using an auto-zero amplifier system to reduce and maintain the amplifier input offset voltage at substantially zero volts. The auto-zero system operates continuously as the multivibrator also generates an output signal. This allows the multivibrator to maintain high stability even as power supply voltage level and operating temperature change.
A multivibrator can be described by dividing it into two sections, the amplifier, and voltage reference. The amplifier compares the voltage level applied to one of its input terminals to that of the voltage reference applied to its other input terminal. The amplifiers output signal state is either high or low depending on the polarity of the voltage level difference between the two input terminals. The switching transition level is the voltage level difference between the two input terminals at which the amplifiers output signal state changes. Monostable and astable multivibrator have an additional section the timing network which sets the length of the pulse duration or oscillation frequency by providing a fixed time period to charge or discharge a capacitor to a voltage reference level. When the voltage level of timing network reaches that of the voltage reference, the amplifier's output signal causes the timing circuit to be either charged or discharged. Ideally the amplifier determines exactly when the voltage level of timing network or external signal applied to its input becomes higher or lower than that of the reference voltage applied to its other input. In multivibrators using high quality passive components (capacitors, resistors, etc.) in the timing network, the amplifier section has the greater parameter variation with supply voltage and temperature. The amplifier's transistor parameters change cause the amplifier offset voltage to change, which in turn changes the pulse duration or frequency of oscillation. This change in pulse duration or oscillator frequency can be reduced by adjusting the input offset voltage of the amplifier to substantially zero volts during a portion of the time period when the amplifier's function is not necessary for the multivibrator to function. This occurs during a fraction of the time period after which the multivibrator changes state. By maintaining the amplifier input offset voltage constant at substantially zero volts, the pulse duration or oscillator frequency stability is increased.
REFERENCES:
patent: 4057740 (1977-11-01), Arguello
patent: 5258664 (1993-11-01), White
patent: 5592128 (1997-01-01), Hwang
patent: 5841306 (1998-11-01), Lim
patent: 5920219 (1999-07-01), Young et al.
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