 Welcome to the session on window detector using opam. Learning outcomes are at the end of session students will be able to explain working of window detector and they can draw the output waveforms for any given input signal and its transfer characteristics. These are like this as its name implies that it gives the detection of the range of voltage. So it is a combination of inverting and non-inverting comparators which are combined together and form a single comparator stage. These two stages are combined with the help of p-n junction diodes. So it will detect the input voltages that are within the specified band. So this is called as window but instead of just comparing a voltage greater than or less than a fixed value it will show you the range of voltage. So it has two reference voltages. So one triggers the opam on detection of upper threshold and one will trigger the opam after detection of the lower threshold that is we reference upper and we reference lower. So the voltages between these two levels is called as window. Figure one shows the circuit diagram for window detector using opam. Opam U1 and U2 are used to detect the upper threshold and lower threshold respectively and where input signal is applied to the opposite terminals that is non-inverting terminal of opam 1 and inverting terminal of opam 2. To this input is applied and these two diodes are used to combine the voltages and provide the output at the window detector. Now we will see what happens for the specific opam stage. First when we in is greater than upper threshold voltage as the upper threshold is connected to the inverting input of the opam and input is applied to the non-inverting input. So here opam's output will saturates to the plus Vsat and diode will be conducting. So when input is greater than upper threshold voltage. In the other case when input voltage is less than Vlt at that time again the opam U2 gives the positive saturation at the output. So in the either cases diode D1 will forward bias in the other case diode D2 will be forward bias. So at that time these two diodes will act as a OR gate when input voltage is within the range of input within the range of upper and lower threshold values at that time both opam's output will saturates to minus Vsat therefore both diodes will not be forward bias. So output voltage will be 0. So we can say here when window is there or when within the range input signal is applied the output voltage is low otherwise it is high. So in detail we will see case 1 when input voltage is less than the lower threshold value and input voltage is also less than the upper threshold voltage. At that time output of opam 1 is minus Vsat diode D1 is reverse biased and here output of U2 is plus Vsat at that time diode D2 is forward biased. So here we can say up to Vlt output voltage is at plus Vsat level because see the circuit diagram where input signal for the opam 2 is applied to the inverting terminal and the threshold voltage is applied to the non-inverting input of the opam. Therefore we have this result for the case 1. In the case 2 where input voltage is greater than the lower threshold voltage and the other case then when input voltage is greater than Vlt. So here threshold level is due to this one that is V in is greater than Vlt. At that time output of opam 1 will be at plus Vsat diode will be conducting and but diode D2 will be reverse biased because U2 is at minus Vsat nothing but due to the condition V in greater than Vlt output of opam 2 will be giving you the diode D2 as reverse biased and thus above Vut also output voltage will be at plus Vsat. So we can say here these two conditions are there which are out of the range. At both these two cases output voltage will be at plus Vsat level but when output voltage is within the window or within the range that it is between the Vut and Vlt range that is input is greater than Vlt but less than Vut and at time both the opams giving you the negative saturation therefore both the diodes are reverse biased. So output voltage will be at 0 volt. Therefore we can conclude here that a logic high output whenever the input voltage is outside the window and the logic low output when it is within the window or within the range of the Vut and Vlt and very important thing the diodes provide the required logical or functionality when either of the output is high current will flow through the diode which will block the short circuit current that would otherwise flow from one output to the other when the two opams having two different states. Figure 2 shows the waveforms for the window detector. So we can say whatever may be the shape of the waveform it will just look at the range of the window. So in between Vlt to Vut output is logic low. In the other case if it is satisfying the any condition it will giving you the output as logic high. So we can say when input is greater than Vut then output is logic 1 as well as when input is less than Vlt at that time also output is logic 1. So this is the waveform for window detector. But another case if you add one more component to the available comparator circuit that is transistor. So as you know for within the range if you are having the output as logic 0. So if it is the if input voltage is within the window. So output is logic 0 and that time transistor will not conduct and therefore you will get the V0 equal to Vcc. Therefore we can say here output will be logic high. So we can change that output also and at that time you can detect the window by observing the logic 1 at the output rather than logic 0 at the output. So we can see the transfer characteristics for the same that is for the circuit shown in figure 3. So see here when output voltage is within the range x axis is representing the input signal y axis representing the output signal. So for within the range output is at plus 5 volt which is giving you the logic high signal. For other cases it will be showing the logic 0. So this is the transfer characteristics for the circuit of window detector when transistor is connected at the output of circuit. Now think and write the correct option. A window detector or a window comparator options are like this has only one usable threshold, uses hysteresis to speed up response, clamps the input positively and detects the input voltage between two limits. Yes as you understood the use of window comparator the option is option 4. Applications are like this it detects or window detectors are used in the industrial alarms level sensor and controls the digital computers and production line testing. Practical example suppose some detail circuit cannot work when input is greater than the 5.5 or less than 4.5 at that time we can use this window detector and get the proper operation of the circuit. But here disadvantages like this there are some slanted edges of the transitions at high frequencies. Therefore to obtain the operation precisely we can use some additional components like Zener diodes. References are like this. Thank you.