? on opamp I-to-V converter schematic

R80, 81 are current source for the D/A.

R60 and C42 make a low pass filter.

tm

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Thanks tm. Could you please elaborate little bit on "R80, 81 are current source for the D/A"? Are they not part of I-V conversion but part of DAC current output?

TIA Ma.jnk

From the data sheet:

The AD1955 audio outputs sink a current proportional to the

input signal, superimposed on a steady bias current. The current-

to-voltage (I/V) converters used need to be able to supply

this bias current, as well as the signal current, or a resistor or

current source can be used to a positive voltage to null this

current in order to center the range of the I/V converters.

If pull-up resistors are used to bring the output of the I/V converters

to 0 V for maximum headroom and THD balance, as shown

in the applications circuits, the following equation can be used:

HTH

tm

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R80 and R81 are as "tm" stated -- note too that they add some compliance to the current outputs, so the "IOUT+" and "IOUT-" aren't perfect current sources (if they were, it sounds like they wouldn't work with the DAC).

R60 and C42 are either there to make the circuit low-pass from input to output, or they are there to stabilize the amplifier circuits against the loading to the loop imposed by C16*, or both.

• In fact, I'm a bit surprised that the circuit is stable at all -- normally any capacitance on the V- input to an op-amp is death on stability. I can only assume that because C16 is connected between two like points on the two op-amps that it's effect gets washed out, but I can't imagine it's a terribly good thing. You certainly wouldn't want to put anything over a few pF at C15 and C17.

Thanks a lot for all the responses. Its pretty clear now.

Ma.jnk