GATE Previous Questions on Asynchronous & Synchronous Counters with Solutions (1987 - Till Date)


1.       A ripple counter using negative edge triggered D flip-flops is shown below. The flip-flops are cleared to ‘0’ at the R input. The feedback logic is to be designed to obtain the count sequence shown in the same figure. The correct feedback logic is : 

Answer:      A
                           Solution :


1.       A 4 bit modulo-16 ripple counter uses JK flip-flops. If the propagation delay of each flip-flop is 50 nsec, the maximum clock frequency that can be used is equal to ……

                        a.       20 MHz
                        b.      10 MHz
                        c.       5 MHz
                        d.      4 MHz

Answer:     C
                            Solution :


1.       A pulse train with a frequency of 1 MHz is counted using a modulo 1024 ripple counter built with JK flip-flops. For proper operation of the counter, the maximum permissible propagation delay per flip flop stage is ____ nsec.

Answer:     50 nSec

2.       A clocked sequential circuit has three states, A, B and C and one input X. As long as the input X is ‘0’, the circuit alternates between the states A and B. if the input X becomes ‘1’(either in state A or in state B), the circuit goes to state C and remains in state C as long as X continues to be 1. The circuit returns to state A if the input becomes ‘0’ once again and from then on repeats its behavior. Assume that the state assignments are A = 00, B = 01 and C = 10.
                        a.       Draw the state diagram of the circuit.
                        b.      Give the state table of the circuit.
                        c.       Draw the circuit using D flip flops.


1.       Synchronous counters are ________ than the ripple counters.
Answer:     Faster

2.       A ring oscillator consisting of 5 inverters is running at a frequency of 1 MHz. the propagation delay per each gate is ________ nsec.
Answer:     100 nSec


1.   A state machine is required to cycle through the following sequence of states:

            ABC :  000  ->  010  ->  111  ->  100  ->  011  ->  101.
One possible implementation of the state machine is shown in figure. Specify what signals should be applied to each of the multiplexer inputs.

                              Solution :   


1.   A sequence generator is shown in figure. The counter status (Q0Q1Q2) is initialized to 010 using preset/clear inputs.
      The clock has a period of 50 ns and transitions take place at the rising clock edge.
                        a.       Give the sequence generates a tQ0 till repeats.
                        b.      What is the repetition rate of the generated sequence?

                 Solution :


1.   The figure is shows a mod – K counter, here K is equal to
                        a.       1
                        b.      2
                        c.       3
                        d.      4
Answer:    C
                  Solution :  

2.   The mod – 5 counter is shown in the figure counts through states Q2Q1Q0 = 000, 001, 010, 011 and 100.
            a.       Will the counter lockout if it happen to be in any one of the unused states?
            b.      Find the maximum rate at which the counter will operate satisfactorily. Assume the     propagation delays of flip-flop and AND gate to be tFF and tA respectively.

                  Solution :    


1.       The ripple counter shown in the given figure is works as a 
                        a.       Mod – 3 up counter
                        b.      Mod – 5 up counter
                        c.       Mod – 3 down counter
                        d.      Mod – 5 down counter
Answer:    D
                 Solution : 

2.       The circuit diagram of a synchronous counter is shown in the given figure. Determine the sequence of states of the counter assuming that the initial state is ‘000’. Give your answer in a tabular form showing the present state QA, QB, QC, J-K inputs (JA, KA, JB, KB, JC, KC) and the next state QA+, QB+, QC+. From the table, determine the modulus of the counter.
Answer:       Mod - 6
                 Solution :


1.   In the given figure, the J and K inputs of all the four flip-flops are made high. The frequency of the signal at output Y is
                        a.       0.833 KHz
                        b.      1.0 KHz
                        c.       0.91 KHz
                        d.      0.77 KHz
            Answer:    B
                 Solution :


1.       For the ring oscillator shown in teh figure, the propagation delay of each inverter is 100 pico sec. What is the fundamental frequency of the oscillator output?
                        a.       10 MHz
                        b.      100 MHz
                        c.       1 GHz
                        d.      2 GHz
Answer:    C
                        Solution :     

2.       The digital block in the figure, realized using two positive edge triggered D flip-flops. Assume that for t<t0, Q1 = Q2 =0. The circuit in the digital block is given by 
Answer:      C
           Solution :


1.       It is required to design a binary mod-5 synchronous counter using AB flip-flop, such that the output Q2Q1Q0 changes as 000 -> 001 -> 010..... and so on. The truth table for the AB flip-flop is given in figure.
            a.       Write down the state table for the mod-5 counter
            b.      Obtain simplified SOP expressions for the inputs A2, B2, A1, B1, A0 and B0 in              terms of Q2, Q1, Q0 and their complements.
            c.       Hence complete the circuit diagram for the mod-5 counter given in the figure using     minimum number of 2 input NAND gate only.

                 Solution :


1.       A 0 to 6 counter consists of 3 flip flops and a combination circuit of 2 input gate(s). The combination circuit consists of
                        a.       one AND gate
                        b.      one OR gate
                        c.       one AND gate and one OR gate
                        d.      two AND gates

Answer:     D
                  Solution :

2.       A 4 bit ripple counter and a 4 bit synchronous counter are made using flip flops having a propagation delay of 10 ns each. If the worst case delay in the ripple counter and the synchronous counter be R and S respectively, then
                        a.       R = 10 ns, S = 40 ns 
                        b.      R = 40 ns, S = 10 ns
                        c.       R = 10 ns, S = 30 ns
                        d.      R = 30 ns, S = 10 ns
Answer:    B
                 Solution :


1.   In the modulo – 6 ripple counter shown in the given figure, the output of the 2 input gate is used to clear the JK flip flops.

The 2 input gate is
                a.       NAND gate
                b.      NOR gate
                c.       OR gate
                d.      AND gate
Answer:    C
                  Solution :


1.       The given figure shows a ripple counter using positive edge triggered flip-flops. If the present state of the counter is Q2Q1Q0 = 011, then its next state Q2Q1Q0 will be

                        a.       010
                        b.      100
                        c.       111
                        d.      101
Answer:    B
                  Solution :


1.       Two D flip-flops are to be connected as a synchronous counter as shown below, that goes through the following Q1Q0 sequence 00 -> 01 -> 11 ->10 -> 00  ->………..

The inputs D0 and D1 respectively should be connected as 
Answer:    A
                                 Solution :


1.       For the circuit shown, the counter state (Q1Q0) follows the sequence
                        a.       00, 01, 10, 11, 00…..
                        b.      00, 01, 10, 00, 01…..
                        c.       00, 01, 11, 00, 01…..
                        d.      00, 10, 11, 00, 10…..
Answer:    B
               Solution :


1.       For each of the positive edge triggered JK flip flop used in the following figure, the propagation delay is ΔT.
  Which of the following waveforms correctly represents the output at Q1?

Answer:    B



1.       What are the counting stages (Q1, Q2) for the counter shown in the figure below?

                        a.       11, 10, 00, 11, 10….
                        b.      01, 10, 11, 00, 01….
                        c.       00, 11, 01, 10, 00…..
                        d.      01, 10, 00, 01, 10…..
Answer:    A
               Solution :


1.       Assuming that all flip-flops are in reset condition initially, the count sequence observed at QA in the circuit shown is

                        a.       0010111….
                        b.      0001011….
                        c.       0101111….
                        d.      0110100….
Answer:    D
               Solution :


1.       When the output Y in the circuit below is ‘1’, it implies that data has

                        a.       Changed from ‘0’ to ‘1’
                        b.      Changed from ‘1’ to ‘0’
                        c.       Changed in either direction
                        d.      Not changed
Answer:    A
               Solution :

2.       The output of a 3 stage Johnson (twisted ring) counter is fed to a digital to analog (D/A) converter as shown in the figure below. Assume all states of the counter to be unset initially. The waveform which represents the D/A converter output Vo is 

Answer:    A
                Solution :

3.       Two D flip-flops are connected as a synchronous counter that goes through the following QB QA sequence 00 -> 11 ->  01 -> 10 -> 00-> ………. The connections of the inputs DA and DB are

Answer:    D
               Solution :


1.       The state transition diagram for the logic circuit shown is

Answer:    D
                 Solution :


1.       Five JK flip flops are cascaded to form the circuit shown in figure. Clock pulses at a frequency of 1 MHz are applied as shown. The frequency (in KHz) of the waveform at Q3 is …………

Answer:    62.5
                 Solution :

2.       The digital logic shown in the figure satisfies the given state diagram when Q1 is connected to input A of the XOR gate. Suppose the XOR gate is replaced by the XNOR gate. Which one of the following options preserves the state diagram?

Answer:    D
                 Solution :

3.       In the circuit shown, choose the correct timing diagram of the output (y) from the given waveforms W1, W2, W3 and W4.
                      a.       W1
                      b.      W2
                      c.       W3
                      d.      W4
  Answer:    C
                Solution :

4.       The outputs of the two flip-flops Q1, Q2 in the figure shown are initialized to 0, 0. The sequence generated at Q1 upon application of clock signal is 

                        a.       01110….
                        b.      01010…..
                        c.       00110….
                        d.      01100…..
Answer:    D
                 Solution :

5.       The circuit shown in the figure is a

                        a.       Toggle flip flop
                        b.      JK flip flop
                        c.       SR Latch
                        d.      Master – Slave D flip flop
Answer:    D
                 Solution :


  1. هل تبحث عن شركة متخصصة فى خدمات التنظيف بالطائف بافضل المعدات والسوائل وثقة تمة فى العمل ودقة فى النتائج كل هذه المميزت توفرها شركة الخليج الشركة الافضل والامثل فى الخدمات المنزلية بالطائف وبما اننا الشركة الافضل والامثل بدون منافس سوف نسعى لتوفر افضل الخدمات باقل تكلفة وبقدر كبير من الاهتمام والدقة عزيزى اينما كنت فى اى منطقة ا وحى تابع لمدينة الطائف اتصل بنا وسوف نصلك فى الحال شركة الخليج للخدمات المنزلية شركة تنظيف منازل بالطائف
    شركة تنظيف فلل بالطائف
    شركة تنظيف خزانات بالطائف
    شركة تسليك مجارى بالطائف
    شركة رش مبيدات بالطائف
    شركة مكافحة نمل ابيض بالطائف
    شركة مكافحة حشرات بالطائف
    شركة عزل اسطح بالطائف
    شركة عزل خزانات بالطائف

  2. فنحن نقوم بكافة أعمال التنظيف للشقق والفلل والقصور نعمل على تنظيف كافة المنزل بداية من الأرضيات سواء كانت بلاط أو سراميك أو رخام و أيضا نقوم بتنظيف فرش الأرضيات سواء موكيت أو سجاد بأكثر من طريقة سواء باستخدام البخار أو بجهاز الرغوة الالية أو باستخدام الفرشاة الاليه. كما نقوم بتنظيف الأثاث بأجود المواد التي لا تؤثر على درجة الالوان أو حالة الأخشاب كما نقوم بتلميع الزجاج ممها بلغ ارتفاعة.

    شركة غسيل موكيت بابها
    شركة عزل خزانات بابها
    شركة تنظيف خزانات المياه بابها
    شركة تنظيف كنب بابها
    شركة رش مبيدات بابها
    شركة رش مبيدات بابها
    شركة مكافحة الحشرات بابها

  3. You've made some good points there. I looked on the internet for additional technology information about the issue and found most people will go along with your views on this website.

  4. It's very useful article with inforamtive and insightful content and i had good experience with this information. We, at the CRS info solutions ,help candidates in acquiring certificates, master interview questions, and prepare brilliant resumes.Go through some helpful and rich content Salesforce Admin syllabus from learn in real time team. This Salesforce Development syllabus is 100% practical and highly worth reading. Recently i have gone through Salesforce Development syllabus and Salesforce Admin syllabus which includes Salesforce training in USA so practically designed.

  5. Very nice blog and articles. I am really very happy to visit your blog. Now I am found which I actually want. I check your blog everyday and try to learn something from your blog. Thank you and waiting for your new post.

    Data Science Course

  6. I am always searching online for articles that can help me. There is obviously a lot to know about this. I think you made some good points in Features also. Keep working, great job !

    Data Science Training

  7. I am really enjoying reading your well written articles. It looks like you spend a lot of effort and time on your blog. I have bookmarked it and I am looking forward to reading new articles. Keep up the good work.
    Data Science Training Institute in Bangalore

  8. Really nice and interesting post. I was looking for this kind of information and enjoyed reading this one. Keep posting. Thanks for sharing.
    Best Data Science Courses in Bangalore

  9. I was very pleased to find this site.I wanted to thank you for this great read!! I definitely enjoying every little bit of it and I have you bookmarked to check out new stuff you post.
    Data Science Course in Bangalore

  10. I don t have the time at the moment to fully read your site but I have bookmarked it and also add your RSS feeds. I will be back in a day or two. thanks for a great site.
    Data Science Training in Bangalore

  11. Wonderful blog found to be very impressive to come across such an awesome blog. I should really appreciate the blogger for the efforts they have put in to develop such an amazing content for all the curious readers who are very keen of being updated across every corner. Ultimately, this is an awesome experience for the readers. Anyways, thanks a lot and keep sharing the content in future too.

    360DigiTMG Artificial Intelligence Course

  12. Truly mind blowing blog went amazed with the subject they have developed the content. These kind of posts really helpful to gain the knowledge of unknown things which surely triggers to motivate and learn the new innovative contents. Hope you deliver the similar successive contents forthcoming as well.

    360DigiTMG Machine Learning Course

  13. Check the customer satisfaction ranking of the Salesforce Consulting Company in Salesforce training in Hyderabad

  14. SAP stands for Systems Applications and Products in Data Processing. SAP, by definition, is also the name of the ERP (Enterprise Resource Planning) software as well as the name of the company.
    tally training in chennai

    hadoop training in chennai

    sap training in chennai

    oracle training in chennai

    angular js training in chennai

  15. Get huge discount on Home and Kitchen Appliances,Split and Window Air Conditioner, Mobiles & Laptops online , Television, Speakers & more electronics at best price.
    price of o general 1.5 ton window ac

  16. An amazing offer! I have quite recently sent this onto a collaborator who had been directing a little schoolwork on this. What's more, he indeed got me supper because of the way that I discovered it for him... haha. So permit me to rephrase this.... Much obliged to YOU for the dinner!! Be that as it may, definitely, thanx for live investing energy to talk about this point here on your site.

  17. Really awesome blog!!! I finally found great post here.I really enjoyed reading this article. Thanks for sharing your innovative ideas to our vision. your writing style is simply awesome with useful information. Very informative, Excellent work! I will get back here. . AWS Course in Chennai

  18. อีกทั้งเรายังให้บริการ เกมสล็อต ยิงปลา แทงบอลออนไลน์ รองรับทุกการใช้งานในอุปกรณ์ต่าง ๆ HTML5 คอมพิวเตอร์ แท็บเล็ต สมาทโฟน คาสิโนออนไลน์ และมือถือทุกรุ่น เล่นได้ตลอด 24ชม. ไม่ต้อง Downloads เกมส์ให้ยุ่งยาก ด้วยระบบที่เสถียรที่สุดในประเทศไทย

  19. If you're searching for a good site, UFA, UEFA Bet casino site. Which can be played as a thorough answer, in a position to reply to Performance and also Quality It's best to have a great deal of the issues. It can easily be a thing very punching & intriguing. Excellently, the items that UFABET football betting is absolutely nothing even with the practical experience of quality. Plus accessibility that will see outcomes It's a model that is really sharp as well as different. Full of efficiency of making money Attractiveness With the best opportunities it's very next to nothing You can find opportunities as well as probabilities for making money. Quality as well as somewhat diverse For people who have arrive at take advantage of the system excellentlyบาคาร่า

  20. อย่างไรก็ตามในการเล่นเกมส์คาสิโนออนไลน์หรือการเดิมพันออนไลน์ชนิดต่างๆคุณจะต้องให้ความสำคัญในเรื่องของการเลือกเว็บคาสิโนออนไลน์เลือกเว็บเดิมพันออนไลน์ที่คุณจะใช้บริการให้ดีคุณจำเป็ สล็อต นที่จะต้องศึกษาและหาข้อมูลเกี่ยวกับเว็บก่อนที่คุณจะตัดสินใจใช้บริการเพื่อความปลอดภัยในการใช้บริการของคุณและเพื่อประโยชน์ในการใช้บริการเว็บที่คุณจะต้องใช้บริการไปอีกนานถ้าคุณใช้บริการเว็บที่ให้บริการที่ดีคุณก็จะมีความสะดวกสบายในการใช้บริการเว็บคาสิโนออนไลน์หรือเว็บเดิมพันออนไลน์ต่างๆ

  21. Our close protection personnel offer complete discretion. And it’s not just about dealing with your physical security chauffeur
    safety. At UK Close Protection Services, we know how to handle the paparazzi, to ensure that personal situations are not public knowledge within half an hour. For this reason, pseudonyms are commonly used.

  22. Really nice and interesting post. I was looking for this kind of information and enjoyed reading this one.
    data scientist course in malaysia


Post Your Feedback (or) Doubts here.......


Email *

Message *