{"id":32796,"date":"2025-06-22T18:44:59","date_gmt":"2025-06-22T18:44:59","guid":{"rendered":"https:\/\/gaviki.com\/blog\/?p=32796"},"modified":"2025-06-22T18:45:00","modified_gmt":"2025-06-22T18:45:00","slug":"perform-a-tran-analysis-in-ltspice-to-simulate-the-comparator-circuit-in-figure","status":"publish","type":"post","link":"https:\/\/gaviki.com\/blog\/perform-a-tran-analysis-in-ltspice-to-simulate-the-comparator-circuit-in-figure\/","title":{"rendered":"Perform a TRAN analysis in LTSpice to simulate the comparator circuit in Figure"},"content":{"rendered":"\n

Perform a TRAN analysis in LTSpice to simulate the comparator circuit in Figure 2. Use a subcircuit to implement the LM324 op-amp model in the “LM324.cir” file: see example posted on Blackboard for details. Connect the positive power supply of the op-amp to 5V. Set the source frequency to 100 Hz and plot waveforms for Vsin and Vout on the same graph. Verify that the value of Vsin that causes a change in Vout is 2.5 V. R1: 10 k\u00ce\u00a9 + Vout 5V T Parameters for Vsin: DC offset voltage = 2.5V, Amplitude = 0.1V, Frequency = 100 Hz R2: 10k Vsin Figure 2<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n

LTSpice Configuration and Simulation<\/h3>\n\n\n\n
    \n
  1. Set up the LM324 subcircuit<\/strong>:\n
      \n
    • Place a *.include<\/code> directive in your schematic pointing to the LM324 model file: .include LM324.cir<\/code><\/li>\n\n\n\n
    • Instantiate the subcircuit by adding a component like X1<\/code> using the name defined in the .subckt<\/code> line of LM324.cir<\/code>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
    • Build the circuit (from Figure 2)<\/strong>:\n
        \n
      • Use two resistors, R1 and R2, both 10 k\u03a9, arranged as a voltage divider. One end of R1 goes to 5V, the junction connects to the inverting input, and the bottom of R2 connects to ground.<\/li>\n\n\n\n
      • Place a sinusoidal voltage source Vsin<\/code> on the non-inverting input, with the following parameters:\n
          \n
        • DC offset = 2.5V<\/code><\/li>\n\n\n\n
        • Amplitude = 0.1V<\/code><\/li>\n\n\n\n
        • Frequency = 100 Hz<\/code><\/li>\n\n\n\n
        • Example: SINE(2.5 0.1 100)<\/code><\/li>\n<\/ul>\n<\/li>\n\n\n\n
        • Connect the op-amp\u2019s +Vs<\/code> to 5V and \u2013Vs<\/code> to ground.<\/li>\n\n\n\n
        • Connect the output (Vout<\/code>) to a resistor load or just monitor it directly.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
        • Set up the .TRAN simulation<\/strong>:\n
            \n
          • Choose a stop time of 50 ms to capture 5 cycles (period = 10 ms).<\/li>\n\n\n\n
          • Use the directive: .tran 0 50m<\/code><\/li>\n<\/ul>\n<\/li>\n\n\n\n
          • Run the simulation and plot<\/strong>:\n
              \n
            • Plot Vsin<\/code> and V(out)<\/code> on the same graph.<\/li>\n\n\n\n
            • Observe the transition point at 2.5V. This is when Vsin<\/code> crosses the reference set by the divider, causing Vout<\/code> to switch between high and low.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n

              Explanation<\/h3>\n\n\n\n

              This circuit uses the LM324 as a voltage comparator. The reference voltage at the inverting input is exactly 2.5V, created by a symmetric voltage divider across a stable 5V supply. The sinusoidal signal fluctuates \u00b10.1V around 2.5V, crossing it twice per cycle. When Vsin<\/code> exceeds 2.5V, the op-amp output saturates near its high rail. When Vsin<\/code> falls below 2.5V, the output drops toward ground. This sharp transition demonstrates classic comparator behavior.<\/p>\n\n\n\n

              The .TRAN<\/code> analysis is ideal here because it lets us visualize real-time voltage transitions rather than just DC or small-signal responses. The clear transitions in Vout<\/code> at the exact moment Vsin<\/code> crosses 2.5V serve as confirmation of correct functionality. This setup is a simple yet effective example of analog signal comparison using op-amps in open-loop mode.<\/p>\n\n\n\n

              \"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"

              Perform a TRAN analysis in LTSpice to simulate the comparator circuit in Figure 2. Use a subcircuit to implement the LM324 op-amp model in the “LM324.cir” file: see example posted on Blackboard for details. Connect the positive power supply of the op-amp to 5V. Set the source frequency to 100 Hz and plot waveforms for […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-32796","post","type-post","status-publish","format-standard","hentry","category-quiz-questions"],"_links":{"self":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/32796","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/comments?post=32796"}],"version-history":[{"count":1,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/32796\/revisions"}],"predecessor-version":[{"id":32799,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/32796\/revisions\/32799"}],"wp:attachment":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/media?parent=32796"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/categories?post=32796"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/tags?post=32796"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}