| Electronics > Projects, Designs, and Technical Stuff |
| Ultra-low THD generator, audio+ band. |
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| MasterT:
--- Quote from: Marco on May 26, 2019, 06:48:17 pm ---You can actually do better than that, the ADC doesn't need to be a limiting factor. As I said in the last thread on this topic. --- End quote --- No like that, we are talking about 3-4 decade frequency range. You have to adjust a filter, otherway one side of the range just disappear . --- Quote from: Audioguru on May 26, 2019, 07:03:15 pm ---I made a sinewave with 10 steps using a high frequency digital oscillator feeding a CD4018 IC and 5 resistors then filtered it with an 8th-order switched capacitor Butterworth lowpass filter IC. Look at Digital Sinewave in Google. The distortion is unmeasurable. I used filter ICs that are now obsolete but today Maxim has some. Since the filter IC has digital settings then its cutoff frequency is set with an internal or external high frequency oscillator. --- End quote --- I haven't seen any filter with THD below 0.01%. Though this approach helps to generate sine by 8-10 bits ADC.Topic is about 20+ (linearity, not dummy bits they put into crappy WM8731 datasheet). --- Quote from: Yansi on May 26, 2019, 08:13:28 pm ---A stupid question: What is this all good for? --- End quote --- Lately I was exploring high resolution ADC area, and find out that requirements for OPA driver for such ADC is really demanding, capable to withstand all terrible EMI coming back to its output from switching capacitor SAR ADC in the frequency range up to 10 MHz (even with CS5361 sampling at 48 kHz). LInearity for simple buffer +-1 (w/o amplification) has to be more than linearity ADC itself, but for much wider freq. range. There are only a few OPA I know, like ADA4841-1 or THS4521. This project about testing this drivers. |
| Marco:
--- Quote from: MasterT on May 26, 2019, 09:33:31 pm ---No like that, we are talking about 3-4 decade frequency range. You have to adjust a filter, otherway one side of the range just disappear . --- End quote --- Low pass filters and analogue switches are cheap, have one per octave. |
| MasterT:
Marco, please open at least one DS for any analog switch. Here is the example, first comes in the folder: --- Quote ---d sin sine-wave distortion f i = 1 kHz; R L = 10 k; see Figure 16 Max Unit V is = 4.0 V (p-p); V CC = 2.25 V; V EE = 2.25 V - 0.04 - % V is = 8.0 V (p-p); V CC = 4.5 V; V EE = 4.5 V - 0.02 - % V is = 4.0 V (p-p); V CC = 2.25 V; V EE = 2.25 V - 0.12 - % V is = 8.0 V (p-p); V CC = 4.5 V; V EE = 4.5 V - 0.06 - % --- End quote --- There is no alternative to do this project in analog domain, old fashion a-la 90-th. It was a time when cheating in the DS becomes a norm, manipulation bit's depth, cpu frequencies, etc. There was a financial group intentionally slow-downing digitalization, creating the traps on analog -to-digital interface. Switching capacitors ADC just one of them, posing a threat to any high resolution circuits even in our days. Digital pre-distortion, feed forward or whats ever they vacabulate it's design I only could think off . |
| Marco:
--- Quote from: MasterT on May 26, 2019, 10:38:58 pm ---Marco, please open at least one DS for any analog switch. --- End quote --- Note the load resistance ... a small amount amount of channel modulation matters with 10s of Ohms of load, less so with 10^9. |
| coppercone2:
--- Quote from: MasterT on May 26, 2019, 10:38:58 pm ---Marco, please open at least one DS for any analog switch. Here is the example, first comes in the folder: --- Quote ---d sin sine-wave distortion f i = 1 kHz; R L = 10 k; see Figure 16 Max Unit V is = 4.0 V (p-p); V CC = 2.25 V; V EE = 2.25 V - 0.04 - % V is = 8.0 V (p-p); V CC = 4.5 V; V EE = 4.5 V - 0.02 - % V is = 4.0 V (p-p); V CC = 2.25 V; V EE = 2.25 V - 0.12 - % V is = 8.0 V (p-p); V CC = 4.5 V; V EE = 4.5 V - 0.06 - % --- End quote --- There is no alternative to do this project in analog domain, old fashion a-la 90-th. It was a time when cheating in the DS becomes a norm, manipulation bit's depth, cpu frequencies, etc. There was a financial group intentionally slow-downing digitalization, creating the traps on analog -to-digital interface. Switching capacitors ADC just one of them, posing a threat to any high resolution circuits even in our days. Digital pre-distortion, feed forward or whats ever they vacabulate it's design I only could think off . --- End quote --- that sounds a bit paranoid... |
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