Amplifier, Timer & Filter Calculators
Gain, timing, and bandwidth all come down to a few resistors and capacitors. Amplifier, Timer & Filter Calculators pick the values. Set op-amp and instrumentation gain, add comparator hysteresis, run a 555, and place a passband.
What Amplifier, Timer & Filter Calculators Set
Analog blocks are mostly resistor ratios. Gain, trip points, oscillator frequency, and passband edges all come from a handful of parts around an op-amp or a timer chip. Amplifier, Timer & Filter Calculators work out those values, then show what the circuit does with them.
Each tool starts from the result you want. Enter the gain, the threshold, the frequency, or the duty cycle, and it returns the components that get there.
Op-Amp Gain
The Op Amp Gain Calculator covers both basic configurations. Inverting gain is the feedback resistor divided by the input resistor, with a sign flip. Non-inverting gain is 1 plus that same ratio.
With 100 kΩ feedback and 10 kΩ input, the inverting stage gives −10 and the non-inverting stage gives 11. The non-inverting form can never go below unity gain, which is why attenuation needs the inverting version or a divider ahead of it.
The Non-Inverting Op-Amp Resistor Calculator runs that backward. Give it the gain you want and it returns the resistor pair, along with the nearest standard values.
Gain costs bandwidth. A voltage-feedback op-amp has a fixed gain-bandwidth product, so closed-loop bandwidth is that figure divided by the gain. A 12 MHz part set to a gain of 10 gives about 1.2 MHz. Push the gain to 100 and you have 120 kHz left.
Instrumentation Amplifier Gain
The Instrumentation Amplifier Gain Calculator handles the classic three-op-amp block used with bridges, strain gauges, and thermocouples.
Gain comes in two stages. The input stage gives 1 plus twice its feedback resistor over the gain resistor. The output difference stage multiplies by its own resistor ratio.
With 25 kΩ input resistors, a 1 kΩ gain resistor, and a unity output stage, total gain is 51. One resistor sets the whole gain, which is why these parts are built with a single external Rg.
Common-mode rejection depends on how well the output stage resistors match. Mismatch there lets shared noise through, so the four resistors matter as much as the gain value.
Schmitt Trigger Thresholds
The Schmitt Trigger Calculator gives the upper and lower trip points of a comparator with positive feedback, and the hysteresis band between them.
A plain comparator chatters when the input crosses its threshold slowly or carries noise. Feedback moves the threshold after each switch, so the input has to travel back across a gap before the output flips again.
The resistor ratio and reference voltage set both thresholds. Wider hysteresis rejects more noise but delays the response to a real signal, so the band is usually set just above the noise on the input.
555 Timer Oscillator
The 555 Timer Astable Oscillator Circuit Calculator returns frequency, period, duty cycle, and the high and low times from two resistors and a capacitor.
Inside the chip, two comparators watch the timing capacitor at one-third and two-thirds of the supply. The capacitor charges through both resistors and discharges through the second one alone, which is what makes the two halves unequal.
| Mode | Result |
|---|---|
| Astable frequency | 1.44 ÷ ((R1 + 2 × R2) × C) |
| Astable duty cycle | (R1 + R2) ÷ (R1 + 2 × R2) |
| Monostable pulse | 1.1 × R × C |
Take R1 at 1 kΩ, R2 at 6.8 kΩ, and C at 100 nF. That gives about 986 Hz at a 53% duty cycle. A monostable with 100 kΩ and 10 µF gives a 1.1 second pulse.
Duty cycle in the standard astable circuit is always above 50%, because the charge path includes both resistors. A diode across R2 bypasses it on discharge and brings the output near square.
Chip choice sets the supply range. The bipolar NE555 runs from about 4.5 V to 16 V, while CMOS versions such as the TLC555 work from about 2 V and draw far less quiescent current.
Bandpass Filters
The Bandpass Filter Calculator works between the two corner frequencies, the centre frequency, bandwidth, and Q.
Centre frequency is the geometric mean of the two corners, not the average. Bandwidth is the gap between them, and Q is centre frequency divided by bandwidth.
A voice band from 300 Hz to 3.4 kHz centres near 1,010 Hz with a Q of about 0.33. That is a wide, gentle passband. A 455 kHz IF filter with 10 kHz of bandwidth has a Q of 45.5, which is sharp and needs high-tolerance parts.
Q below about 0.7 usually means a low-pass and a high-pass stage in series works better than a single tuned section. Above roughly 10, component tolerance and op-amp bandwidth start to dominate the result.
Common Mistakes
Forgetting the gain-bandwidth limit. A gain of 100 on a 12 MHz part leaves only 120 kHz of bandwidth.
Expecting 50% duty from a plain 555. The charge path is longer than the discharge path, so it always runs above half.
Averaging filter corners. Centre frequency is the geometric mean, so 300 Hz and 3.4 kHz centre at 1,010 Hz, not 1,850 Hz.
Using a bare comparator on a slow signal. Without hysteresis the output oscillates around the threshold.
Amplifier and Timer FAQs
How do I set op-amp gain?
Pick the resistor ratio. Inverting gain is the feedback resistor over the input resistor, so 100 kΩ and 10 kΩ give −10. Non-inverting gain is 1 plus that ratio, so the same parts give 11. Keep the input resistor large enough not to load the source, and small enough to keep noise down. Values in the 1 kΩ to 100 kΩ range suit most audio and sensor work.
Why does my amplifier lose bandwidth at high gain?
Voltage-feedback op-amps hold gain times bandwidth roughly constant. A part rated at 12 MHz gives about 1.2 MHz at a gain of 10 and only 120 kHz at a gain of 100. Splitting the gain across two stages, for instance 10 in each, keeps more bandwidth than one stage of 100.
How do I calculate 555 astable frequency?
Divide 1.44 by R1 plus twice R2, times the capacitance. With 1 kΩ, 6.8 kΩ, and 100 nF, that comes to about 986 Hz. Duty cycle is R1 plus R2 over R1 plus twice R2, or about 53% here. For a one-shot instead, the pulse is 1.1 times R times C.
How do I get a 50% duty cycle from a 555?
Add a diode across R2 so the capacitor charges through R1 and discharges through R2 alone. With R1 and R2 equal, the output sits close to square, though the diode drop leaves a small imbalance. A CMOS 555 or a divide-by-two flip-flop on the output gives a cleaner result.
What does hysteresis do in a comparator?
It separates the switch-on and switch-off thresholds. Once the output flips, feedback shifts the threshold away from the input, so noise near the trip point cannot flip it back. Set the band a little wider than the noise on the signal. Too wide and the circuit responds late to real changes.
What is Q in a bandpass filter?
Q is centre frequency divided by bandwidth, so it measures how narrow the passband is. A 1 kHz filter passing 300 Hz to 3.4 kHz has a Q near 0.33, while a 455 kHz filter with 10 kHz of bandwidth has a Q of 45.5. High Q means sharper selectivity, more ringing, and tighter component tolerances.