In a certain amount this can be compensated by D2.1, R2.1 and C2.1. Thus, the signal's average value becomes more positive the more slopes are present in the bitstream. Though the ♜'s CMOS outputs are specified to be fully symmetrical, i.e., the pulldown FET is as strong as the pullup FET, it turned out that the signal's positive and negative slopes were not as equal as could be expected. The ADR4533A features typically 4 ppm/☌ and 25 ppm/1000 h. I provided a simple 3.3 V source with a TL431 as reference and alternatively an improved (and of course more expensive) 3.3 V source using the ADR4533A. Thus the ♜'s power supply must be precise. The ♜'s bitstream output is directly used as an analog signal, i.e., there is no extra 1-bit digital to analog converter provided. Because the analog (and thus reference) levels are the ♜'s power supply rails of 0 and 3.3 V, the 1 kHz signal has an approximate value of 2,97 V PP resp 1.05 V RMS. The reason for these 90% instead of 100% is declared later. The ♜'s bitstream's 1 st order modulator clock frequency is 800 kHz and it is modulated by the 1 kHz sine wave with a modulation index of 90%. This also allows that the BNC connector's ground is connected to the negative line of the balanced outputs. Power Supplyīecause the generator should neither have a direct (galvanic) connection to its enclosure nor to the external power supply, I used a DC-DC converter with floating outputs for the internal ☑2 V supply. So far there is nothing exotic (except probably the delta sigma sine wave generator), but the details are important. Finally it is amplified and converted to a balanced signal for the XLR outputs. This bitstream is low-pass filtered in order to remove the quantization noise, divided either in 5 steps of 3 dB or with a potentiometer from 0 to 10 V RMS. The sine wave "leaves" the ♜ as a delta sigma bitstream. The sine wave is generated by a microcontroller, a simple and cheap TI MSP430F2011. Thus I hope to have achieved a precision of about 0.1%. I assumed the Agilent 34410A to be better calibrated than my HM8112 and calibrated the generator using the correction factor I got from the comparison. Both matched well or even clearly within these specified values. I compared it to a probably much better Agilent 34410A multimeter. I own a quite good but old multimeter, a Hameg HM8112-2, which displays up to 6½ digits even in AC-ranges and was originally specified with an error of less than 0.3% of reading + 0.1% of full scale in the here relevant AC-ranges of 2 V RMS and 20 V RMS. I don't specify the precision of the level, because I simply have no means to measure it as precise as I would like and ought to. Output amplitude: 9, 12, 15, 18 21 and 24 dBu and 0 - 10 V RMS variable.Output frequency: 1 kHz, crystal controlled.Output connectors: 2 (paralleled) XLR jacks, balanced, + 1 BNC jack.It is not too difficult to reproduce this device. This is actually not meant to be a DIY project, but should anybody be interested in reproducing it, I can hand out the Gerber and Excellon files for the PCB and the hex and possibly even the source code for the ♜. Here I describe the circuit diagram and the sine wave generating microcontroller's firmware. Thus I laid the emphasis on a constant and precise output voltage. This is a delta sigma based analog 1 kHz sine wave generator with the main intention to generate a precise 1 kHz tone for calibration of analog level meters. At 4.5 volts, a smaller resistor can be used.DS1kGen - Precision 1 kHz Audio Sine Wave Generator Electronic PagesĭS1kGen - Precision 1 kHz Audio Sine Wave Generator The 51 ohm resistor limits the current to less than 200 mA to prevent overloading the timer output at 9 volts. The series capacitor (100 uF) increases the output by supplying an AC current to the speaker and driving it in both directions rather than just a pulsating DC current which would be the case without the capacitor. In the circuit on the right, the speaker is directly driven from the 555 timer output. Lower volume levels can be obtained by adding a small resistor in series with the speaker (10-100 ohms). Lower frequencies can be obtained by increasing the 6.2K value, higher frequencies will probably require a smaller capacitor as R1 cannot be reduced much below 1K. Frequency is about 1.44/(R1 + 2*R2)C where R1 (1K) is much smaller than R2 (6.2K) to produce a near squarewave. A small capacitor is used at the transistor base to slow the switching times which reduces the inductive voltage produced by the speaker. In the circuit on the left, the speaker is isolated from the oscillator by the NPN medium power transistor which also provides more current than can be obtained directly from the 555 (limit = 200 mA). This is a basic 555 squarewave oscillator used to produce a 1 Khz tone from an 8 ohm speaker.
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