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Op-amp properties; square wave generator

Short answer

Ideal op-amp properties: infinite open-loop gain, infinite input impedance, zero output impedance, infinite bandwidth, infinite CMRR. The square wave generator is an astable multivibrator with a comparator and RC network; the capacitor charges/discharges between ±βVsat, toggling the output to produce a square wave of period T≈2.2RC when R1=R2.

Mention any five properties of ideal Op-Amp. Draw the circuit diagram and explain the operation of square wave generator using Op-Amp.

Properties of an ideal op-amp

  1. Infinite open-loop voltage gain (A = ∞).
  2. Infinite input impedance (Zin = ∞), so the input current is zero.
  3. Zero output impedance (Zout = 0).
  4. Infinite bandwidth (response from 0 Hz to ∞).
  5. Infinite common-mode rejection ratio (CMRR = ∞), so common-mode noise is rejected.
  6. Zero offset voltage: the output is zero when both inputs are zero.

Square wave generator (astable multivibrator)

A square wave generator is an op-amp used as a comparator with positive feedback, together with an RC charging network. It needs no input signal.

          +----------[ R ]-----------+
          |                          |
          |         |\               |
          +---------|- \             |
          |         |   >------------+----o Vo
         === C   +--|+ /             |
          |      |  |/               |
         GND     +-------[ R2 ]------+
                 |
               [ R1 ]
                 |
                GND

Circuit: the output is connected through R to the inverting terminal, where capacitor C connects to ground. The non-inverting terminal receives a fraction of the output through the divider formed by R2 (from the output) and R1 (to ground).

Feedback fraction: β = R1/(R1 + R2).

Operation

  1. Suppose the output is at +Vsat. The reference at the non-inverting input is +βVsat. C charges towards +Vsat through R.
  2. When the capacitor voltage reaches +βVsat, the inverting input exceeds the non-inverting input and the output switches to −Vsat.
  3. The reference now becomes −βVsat. C discharges and then charges towards −Vsat.
  4. When the capacitor voltage reaches −βVsat, the output switches back to +Vsat.
  5. This repeats, giving a square wave between +Vsat and −Vsat. The capacitor voltage rises and falls exponentially between ±βVsat.

Time period: T = 2RC ln[(1 + β)/(1 − β)]

If R1 = R2 (β = 0.5), T = 2RC ln 3 ≈ 2.2 RC, so f = 1/(2.2 RC).

✓ Answer checked by Claude Opus 5.5 (high effort)

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