TRANSISTOR CIRCUITS FOR ANALOG AND DIGITAL SYSTEMS 



327 



increases the switching time. The circuit shown in Figure 21 does not 

 misfire when used with voltage waveforms having slopes as small as 25 

 millivolts per microsecond, at the reference level. 



6.0. A TRANSISTOR VOLTAGE ENCODER 



6.1. Circuit Arrangement 



The transistor circuits previously described can be assembled into a 

 voltage encoder for translating analog voltages into equivalent time 

 intervals. This encoder is especially useful for converting analog informa- 

 , tion (in the form of a dc potential) into the digital code for processing 

 in a digital system. Fig. 22 shows a simplified block diagram of the 

 encoder. The voltage I'amp generated by the integrator is applied to 

 amplitude selector number one and to one input of a summing amplifier. 

 The amplitude selector is a dc amplifier which amplifies the voltage ramp 

 in the vicinity of zero volts. Voltage comparator number one, which 

 follows the amplitude selector, generates a sharp output pulse at the 

 exact instant of time that the voltage ramp passes through zero volts. 



The analog input voltage, which has a value between and —15 

 volts,* is applied to the second input of the summing amplifier. The 

 output voltage of the summing amplifier is zero whenever the ramp 



INTEGRATOR 



N0.1 



N0.1 



3000^65 



SUMMING 

 AMPLIFIER 



AMPLITUDE 

 SELECTORS 



VOLTAGE 

 COMPARATORS 



ANALOG 



INPUT VOLTAGE 



0-^-16V 



N0.2 



N0.2 



Fig. 22 — • Simplified block diagram of voltage encoder. 



* If the analog input voltage does not lie in this range, then the voltage gain 

 of the summing amplifier must be set so that the analog voltage at the output of 

 the summing amplifier lies in the voltage range between and +15 volts. 



