1701 built-in resonator vs external one

Hi Skfir,

Perhaps you misunderstood the datasheet. There is no built-in resonator, only a built-in oscillator amplifier. An oscillator in its simplest form is a series of inverters, such as in the case of a simple ring oscillator: http://en.wikipedia.org/wiki/Ring_oscillator

The oscillator amplifier requires an external crystal resonator to complete the circuit, forming a crystal oscillator circuit.

In other words, the completed circuit requires both the internal components and the external crystal resonator to operate.

See this app note from Microchip for more details: http://ww1.microchip.com/downloads/en/appnotes/00826a.pdf

The "amp" in figure 1 is inside the ADAU1701, whereas the "filter" is basically the crystal resonator plus the capacitors which are externally provided.

Unfortunately, there is a bit of ambiguity in the naming conventions here (the terms are often incorrectly used interchangeably), so people often get confused.

I believe the technically accurate name for the two-terminal crystal component itself is a crystal resonator (in other words, a crystal with a resonant frequency). The name for a complete circuit consisting of a crystal resonator plus an amp to drive it is a crystal oscillator. The Wikipedia article does a pretty good job of clearing up any confusion between the two: http://en.wikipedia.org/wiki/Crystal_oscillator

Message was edited by: Brett Gildersleeve (added more details to remove ambiguity)

Understand now, thank you Brett!!

Hello Skfir,

Unlike some microcontrollers, DSP chips have no internal (self-contained) clock options because presently, only a crystal can supply a sufficiently stable clock. The clock ultimately times each sample into the ADC, through the DSP and out the DAC. Thus, any irregularities (called jitter) is heard as noise. Only worse, because while the "hiss" of analog recordings merely adds to the desired sound, jitter modulates it. It sounds really bad. In your application, jitter would reduce the resolution of your echo measurements.

Best regards,

Bob

Thank you Bob!!