Its a consequence of the design of the differential sigma-delta modulator, which will be very proprietry...
Well, if you know how much it is, you can take it into account when designing your circuit around it.
Can you give me a simple calculation example so I can understand how it matters ? Is this resistance in series with the output ? If the output will be forced to be fixed by the op-amp in the i/v converter, will this resistance force the internal output of the constant current source to vary in voltage according to the musical program ?
Every signal source can be thought of as an ideal voltage source in series with an impedance (as here), or equivalently as an idea current source in parallel with an impedance (the less commonly used Norton source representation).
For distortion you need to know how linear the source impedance is (if its not linear you'd better not draw much current from it). For a high end voltage DAC it will be pretty linear, but you probably still want to buffer the output to avoid loading that impedance.
For a current DAC the Norton representation is the appropriate one, and its usual there to load with a virtual short circuit as the shunt impedances are definitely not linear in a current output DAC.
For distortion you need to know how linear the source impedance is (if its not linear you'd better not draw much current from it). For a high end voltage DAC it will be pretty linear, but you probably still want to buffer the output to avoid loading that impedance.
For a current DAC the Norton representation is the appropriate one, and its usual there to load with a virtual short circuit as the shunt impedances are definitely not linear in a current output DAC.
Yes, that output resistance is in series with the output. You can say that the output of the convertor is an ideal voltage source with that output resistance in series.Can you give me a simple calculation example so I can understand how it matters ? Is this resistance in series with the output ? If the output will be forced to be fixed by the op-amp in the i/v converter, will this resistance force the internal output of the constant current source to vary in voltage according to the musical program ?
I have not looked at the datasheets of those convertors, so it may not apply in this specific instance. But suppose you use an inverting amp after the output. In an inverting amp, one of the resistors of the feedback would be in series with the output. So that output resistor would be in series with that feedback resistor and it would be important to add it to the feedback resistor to get the final gain of the inverting amp. Likewise that output resistance will make a low pass filter with any capacitance that sits at the output.
Every signal source can be thought of as an ideal voltage source in series with an impedance (as here), or equivalently as an idea current source in parallel with an impedance (the less commonly used Norton source representation).
For distortion you need to know how linear the source impedance is (if its not linear you'd better not draw much current from it). For a high end voltage DAC it will be pretty linear, but you probably still want to buffer the output to avoid loading that impedance.
For a current DAC the Norton representation is the appropriate one, and its usual there to load with a virtual short circuit as the shunt impedances are definitely not linear in a current output DAC.
So, the equivalent schematic of the current output es9038Pro is like in my drawing ?
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Almost. Resistor is referenced to VCC/2, not GND.So, the equivalent schematic of the current output es9038Pro is like in my drawing ?
The output impedance is the equivalent resistance present in series with the output. You need to take this value into account when you design the reconstruction filter at the output of the DAC.Can you give me a simple calculation example so I can understand how it matters ? Is this resistance in series with the output ?
I'm guessing that the DACs that have the output impedance specified are voltage-output types. So for the design process you'd assume that the DAC is an ideal voltage source with the output impedance added in series. The ones that don't have the output impedance specified are likely current-output types. That's just an educated guess. You could look up their respective data sheets.
Tom
ESS DACs appear to be of the rather uncommon switched-resistor type. Those silicon resistors have voltage cooefficient which is why ESS recommends running the output pins into a fixed voltage virtual GND node just like true current-output types.I'm guessing that the DACs that have the output impedance specified are voltage-output types. So for the design process you'd assume that the DAC is an ideal voltage source with the output impedance added in series. The ones that don't have the output impedance specified are likely current-output types. That's just an educated guess. You could look up their respective data sheets.
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