Products > Test Equipment

Question: Cheap pure sine wave genertor 1khz?

<< < (16/19) > >>

Verticon:
Yes, I've built several of these state variable oscillators. But mostly with wide frequency range from 10Hz to 100kHz. At 1 kHz they have a typical distortion level below 0.001% even with OP-AMPs like 5534. The 1980 Tektronix SG505 (wide frequency range) with a similar oscillator technique has a typical 1kHz distortion of 0.0003% which corresponds to -110dB.

So if they mean 0.0064% (which is only -84dB) it is an easy task. But even -124dB should be not out of reach with this oscillating principle tweaked for a fixed frequency.

trobbins:
A recent enhancement on the approach that uses a soundcard to generate %HD levels down at the 0.00001% level is that REW introduced a 'coherent averaging' capability mid last year.  That option allows the noise floor for assessing HD levels to be dropped by quite a few dB, and hence assists the nulling process of HD contributions.  It should also assist any process that tries to insert a notch filter in the loopback path as a way to confirm that the DAC is actually generating such low levels of HD%, compared to the DAC + ADC generating such low levels.

Grandchuck:
trobbins, do you happen to know if REW software plus an interface like the Focusrite Scarlett Solo would be capable of measuring THD levels around -120dB or better?

Thanks

Marco:

--- Quote from: trobbins on December 28, 2021, 12:17:30 am ---should also assist any process that tries to insert a notch filter in the loopback path as a way to confirm that the DAC is actually generating such low levels of HD%, compared to the DAC + ADC generating such low levels.

--- End quote ---
In principle a low pass filter is enough to distinguish adc distortion from dac distortion, though a notch filter simplifies the calculation.

pandy:
Apologies for reviving this thread but as no one before proposed something that will be probably simplest, cheapest yet very clean source of for example sine (but not only) signal - circuit using some memory (uC?), sequencer (uC or dicrete logic) and additional elements (like for example CD4000 series powered with for example 15V to increase overall SNR). In memory single bit delta-sigma i.e. PDM single bit sine (or other) waveform is stored and sequentially outputted to single pin - i.e. serial out - with sufficient oversampling and wise embedded resources use probably simple uC with sufficient memory will be more than OK - with help of common SPI output it may deliver 1kHz at few MHz sample rate efficiently turning such uC into sinewave signal source with very high quality beyond typical 16..20 bit - something like SACD audio quality.

2000 sine samples (single sine period) with 64 times oversampling will require approx 16KB table - 128 times oversampling will be 32K etc...
Sine frequency can be changed by using different clock. There is possibility to use some tricks to reduce required memory and/or to increase sampled signal phase accuracy if signal is like sine - similar to tricks used in DDS/NCO.

If uC is equipped with PWM then using high order delta sigma (multibit) very high quality signal reproduction can be created even with relatively low PWM resolution (<8 bit) but high sample rate - there is many possibilities to use digital resources and get high quality analog signal.

To create PDM, open source software can be used for example https://pcmdsd.com/Software/PCM-DSD_Converter_en.html

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod