An analog signal to discrete time interval converter (ASDTIC) is a specialized kind of an

analog-to-digital converter In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide ...

, which converts the

analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analog ...

input signal (e.g. voltage or current) to time intervals between pulses. This conversion is a type of

Pulse-width modulation Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. The average value of voltage (and current) fed ...

(PWM). The origin of the term ASDTIC lies with

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around 1970. ASDTIC were used in the control of

DC-DC converter A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low (small batteries) ...

s. For use in space-rated systems, reliable

hybrid circuit A hybrid integrated circuit (HIC), hybrid microcircuit, hybrid circuit or simply hybrid is a miniaturized electronic circuit constructed of individual devices, such as semiconductor devices (e.g. transistors, diodes or monolithic ICs) and ...

s were developed to implement the ASDTIC function.

Operation

The DC-DC converters under study in this workResearch contract NAS12-2017, December 1969 – October 1970, TRW for

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had a similar form as a DC chopper or switching regulator. A

bipolar transistor A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar t ...

switches current flowing into an L-C network of an

inductor An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a c ...

and

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

. To reduce , the transistor is always turned either fully off or fully on. Control of this transistor is derived from a control circuit that supplies a series of pulses. In the circuits studied here, the pulses are all of equal length. The overall ''ON'' time or

mark/space ratio A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle. As a formu ...

of the pulse train (and thus the output power delivered) is controlled by varying the interval between pulses. Closely spaced pulses increase output. This control signal is derived by use of an ASDTIC circuit. The ASDTIC circuit used is based around an

integrator An integrator in measurement and control applications is an element whose output signal is the time integral of its input signal. It accumulates the input quantity over a defined time to produce a representative output. Integration is an importan ...

and a

threshold detector Threshold may refer to: Architecture * Threshold (door), the sill of a door Media * ''Threshold'' (1981 film) * ''Threshold'' (TV series), an American science fiction drama series produced during 2005-2006 * "Threshold" (''Stargate SG-1''), ...

. The incoming signal is integrated over time and when it exceeds a threshold, a control pulse is generated by the ASDTIC. Within the converter control circuit outside the ASDTIC, a One-Shot Pulse Generator then generates a pulse of constant length to drive the switching transistor. The ASDTIC approach was taken in an attempt to improve the regulation and stability of previous switching regulators with

linear Linearity is the property of a mathematical relationship (''function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear r ...

control systems. These used an

error signal In control engineering a servomechanism, usually shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the action of a mechanism. On displacement-controlled applications, it usually includes a built-in ...

derived from the converter's DC output voltage and had a tendency to behave as

underdamped Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples in ...

second-order Second-order may refer to: Mathematics * Second order approximation, an approximation that includes quadratic terms * Second-order arithmetic, an axiomatization allowing quantification of sets of numbers * Second-order differential equation, a di ...

systems which were prone to oscillations in their output. The ASDTIC control system of Schoenfeld & Yu was an attempt to improve this dynamic performance. An additional AC component was measured, from the voltage across the output inductor, and this new AC loop signal was also supplied to the integrator within the ASDTIC. Such a second AC loop went beyond the claims of the original Schwartz ASDTIC patent Performance of the new control technique was good: converter stability was enhanced, and its dynamic performance characteristics greatly improved.

References

{{Reflist , refs= {{Cite patent , country=US , number=3659184 , title=Analog signal to discrete time interval converter (ASDTIC) , fdate=1970-02-11 , pubdate=1972-04-25 , inventor=Schwarz, Francisc C. , assign=

{{Cite web , title= ASDTIC control and standardized interface circuits applied to buck, parallel and buck-boost dc to dc power converters , first=A. D. , last1=Schoenfeld , first2=Y. , last2=Yu , date=February 1973 , publisher=

, id=NASA CR-121106 , url=https://www.researchgate.net/publication/23613076 {{Cite web , title=The application of the analog signal to discrete time interval converter to the signal conditioner power supplies , first=A. D. , last1=Schoenfeld , first2=Y. , last2=Yu , publisher=

, date=August 1, 1973 , id=NASA CR-120906 , url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740021458.pdf Power supplies Analog circuits