Often, one needs a simple low voltage sinusoidal oscillator with good amplitude and frequency stability and low harmonic distortion; here, the Peltz oscillator becomes a viable candidate. Please see the Peltz oscillator Analog Devices Wiki page here (Ref. 1) and a discussion on my Peltz oscillator here (Ref. 2).
Shown in Figure 1, the Peltz oscillator requires only two transistors, one capacitor, one inductor and one resistor. In this configuration, the output voltage is a ground referenced, direct coupled, low distortion sinewave, swinging above and below ground at ~1 VBE, while operating from a low negative supply voltage (AAA battery).
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| Figure 1. | Basic configuration of a Peltz oscillator with a low component count yielding a low distortion sinewave output. |
The oscillating frequency is shown:
A simplified analysis shows the minimum negative supply voltage (VEE) is:
Where VT is the Thermal Voltage (kT/q), Z is the total impedance “seen” at the parallel resonant LC network, VBE is the base emitter voltage of Q1 [VT×ln(IC/IS)], and IS is the transistor saturation current.
Here’s an example with a pair of 2N3904s, a 470 µH inductor, 0.22 µF capacitor, and a 510 Ω bias resistor, powered from a single AAA cell (the oscillator actually works at ~0.7 VDC), producing a stable, low noise ~16 kHz sinewave as shown in Figure 2, Figure 3, and Figure 4.
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| Figure 2. | Peltz oscillator output with a clean 16 kHz sinewave. |
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| Figure 3. | Spectral view of sinewave showing fundamental as well as 2nd and 3rd harmonics. |
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| Figure 4. | Zoomed in view of ~16 kHz sinewave. |
Note the output frequency, peak to peak amplitude and overall waveform quality is not bad for a 5-element oscillator!
