Frequent contributor Nick Cornford just lately shared design concepts incorporating cool circuits for linear-in-pitch voltage-controlled oscillators (LPVCOs):
- Revealing the infrasonic underworld cheaply: Half 1 and Half 2
- A pitch-linear VCO: Half 1 and Half 2
Wow the engineering world together with your distinctive design: Design Concepts Submission Information
The linear in pitch perform, which makes output frequency proportional to the antilog of voltage, is fascinating as a result of it offers a greater perceptual interface to the inherently logarithmic human ear than a linear frequency.
One measure of the efficiency of an LPVCO is its octave vary. That’s the ratio of highest to lowest frequency that its output spans, expressed because the binary (base 2) logarithm of the ratio. Two octaves (22 = 4:1) is nice. Three octaves (23 = 8:1) is healthier. The LPVCO in Determine 1 does seven (27 = 128:1).
Determine 1 A seven-octave LPVCO includes Q1 Q2 antilog pair that converts the 0 V to five V Vin, to a 1 µA to 128 µA Ic2, for a proportional 27 = 128:1 change in C1 ramp fee and U1 oscillation frequency. Counter U2 then scales the U1 oscillation frequency by 4 and converts to a three-level, very vaguely “sine-ish,” output waveform.
Right here’s the way it works.
Management voltage Vin is scaled by a voltage divider (R1/R2 + 1) = 34:1 and utilized to the Q1 Q2 exponential-gain present mirror. There, it’s level-shifted and temperature-compensated by Q1, then anti-logged by Q2 to provide
Ic2 = 2(1.4Vin) µA. The ensuing C1 timing ramp spans from 5 ms (for Vin = 0) to 40 µs (for Vin = 5 V). The ramp ends when it crosses analog timer U1’s 1.67-V set off degree and is reset by way of R5 and D1 to U1’s threshold degree of three.33 V, beginning one other oscillation cycle. The ensuing sawtooth will due to this fact repeat at F = Ic2/(1.67C2) = 2(1.4Vin) µA / 5nCb = 200 (2(1.4Vin) ) Hz.
Nick’s pretty designs present that brief pulses equivalent to U1’s output spikes require conversion to a waveshape with a much less intense harmonic content material if we need to hear a listenable audio output. Subsequently, U2’s switch-tail counter divides U1’s oscillation frequency by 4. This produces a hardly sinusoidal, however not less than considerably much less annoying, tri-level 50 Hz to 6400 Hz last output.
Thanks go to Nick for a enjoyable and well-conceived design matter, and naturally to editor Aalyia for her pleasant Design Thought division format that makes such pleasant collaboration potential!
Stephen Woodward’s relationship with EDN’s DI column goes again fairly a good distance. Over 100 submissions have been accepted since his first contribution again in 1974.
Associated Content material
- Revealing the infrasonic underworld cheaply, Half 1
- Revealing the infrasonic underworld cheaply, Half 2
- A pitch-linear VCO, half 1: Getting it going
- A pitch-linear VCO, half 2: taking it additional
- Can a free working LMC555 VCO discharge its timing cap to zero?
The submit Seven-octave linear-in-pitch VCO appeared first on EDN.
