In the practical side, for the proper working of this circuit the positive half of the input signal must have at least 5uS pulse width and for the negative half it must be greater than or equal to 5uS.įor calibration adjust the offset adjust trimpot to obtain 0V at the output with no input frequency applied. The TC9400 manufacturers claim that it can accept a signal of any frequency at its input. In simple words this section of the circuit can be generally termed as a level shifter. The clamp circuit using diode D2 prevents the input from going far negative in order to turn on the internal comparator. The potential divider network comprising of R6 and R7 makes sure that the input threshold tracks the supply voltage always. Resistor R biasis used to set the bias current of the IC. The voltage across the integrating capacitor C int is retained because the only discharge path available is the 1M resistor R int which is a too high and the voltage across C int is the output voltage. Each time the input frequency wave form crosses zero towards positive direction, the output of the internal comparator goes high and this disables the C ref charge/discharge circuit which creates a short circuit across the C ref leads. In the single supply operation the reference voltage is the potential difference between pin 2 and 7 of the TC9400. The 3uS delay circuit enables the C ref charge/discharge circuit after 3uS and this connects the C ref to the reference voltage and this charges the integrating capacitor C int a specific amount of voltage. Whenever the input signal to the pin 11 of IC1 crosses zero to the negative direction the output of the internal comparator goes low. In order to trip the comparator the amplitude of the input frequency must be greater than +/-200mV.Below this level the circuit will not work at any situation. The input frequency is applied to the pin11 (non inverting input of the internal comparator). The circuit generates an output voltage that is proportional to the input frequency. In the circuit shown above the TC9400 is wired as a F to V converter that operates from a single supply.
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