The Davone Module in Detail
The Davone module is a so called mixed signal PCB design, meaning it has both analog circuits and digital circuits on a single board. Through a careful lay out of components and multipoint high frequency grounding, the mixing of analog and digital signals is avoided while retaining the shortest signal paths. The main components are highlighted below:
- The microcontroller is the brain of the Davone module. It's large memory contains the entire DSP and functional program, also called the firmware, written by Davone. This way the often used separate EEPROM memory is avoided and replaced with the internal memory of a microcontroller. This is much better protected against unpredictable power supply swings and therefore more reliable as long term memory storage. During normal operation, when a music signal is detected, it programs the DSP and checks if it is functioning well. If the temperature is within the set limits, it will program the DAC and unmute the amplifier. It will continuously monitor the presence of the mains power and the status of the input signal and act accordingly to ensure stable and noise free operation and reduce power consumption whenever possible.
- Quartz Crystal Oscillator for low jitter, packaged in ceramics with metal lid for high precision and reliability. The oscillator signal is used to generate a clock signal which is fed into the DSP's dejitter circuits to guarantee that jitter related clocking errors are avoided. The master clock output of the DSP is fed directly into the DAC with a jitter less than 100ps rms.
- Within the 32 bit Digital Signal Processor, the wireless received signal is first routed into the Asynchronous Sampling Rate Converter (ASRC) to minimise jitter. Then the signal is filtered with a FIR filter into the high and low bands and also small imperfections of the drivers are removed.
- The high performance 32 bit Velvet Sound AKM Delta Sigma DAC is handling the conversion to analog. The power is supplied through ultralow noise linear regulators and ample capacitance of different types for a virtual battery like performance.
- The fully balanced output stage minimises noise and is connected directly to the balanced input of the ICE power amplifier.
- The multipoint high frequency ground ensures lowest impedance returns paths to ground for high frequency noise and effectively prevents ground loop noise.
High Frequency Design
High frequency digital signals above 1 MHz, like for example the master clock, need to be routed carefully to maintain high signal integrity. Ideally the connections should be short and direct, but often this is not possible because another signal line crosses it’s path. Textbook four layer print design would divert the trace through a so called via to the bottom layer to cross the obstacle. The second and third layer are used for the ground and power supply planes and therefore already occupied.
However, in high frequency circuit design it is vital to keep the distance between the forward and return current traces at a minimum (the path of least inductance). It is therefore much better to route the forward current through the third layer instead of the fourth. That way the return current only has to switch sides on the second layer instead of also jumping planes through one extra via with possible added ground plane noise as a consequence. The improved high frequency current flow is shown in the image above and explained below.
- Trace on top layer of Printed Circuit Board (PCB). High frequency forward current shown in red flows at underside of trace.
- A small copper tube, or so called "via", connects the top and third layer. The via's are visible at the top of the PCB as tiny holes. The forward current flows at the outside of the via.
- Trace on third PCB layer. The high frequency forward current in red now flows at top of trace.
- The Second PCB layer is a continuous plane at ground potential. The return current in blue flows at the bottom of the plane nearest the forward current on the third layer, following the path of least inductance.
- Around the via, the return current now simply switches sides of the ground plane. The distance between the forward and return current is minimal at all times and signal integrity is optimal.
- Bottom layer of PCB. This is where normally the forward current trace would be routed to.