Advertisement
https://www.ecdesigns.nl
Batteries are used in the examples above to simplify the theory of operation, in reality these are linear
power supplies as shown in block diagram above. Each set of switches (top, bottom) represents a
separate divider. We have: two batteries, an RCA output (VU meter), two equal resistors R, and two
electronic switches. Batteries are a short circuit for AC signals (audio signals). The resistor sets attenuate
the battery voltage in order to generate an analogue output signal.
A/D) Upper switches on maximum plus, lower switches on maximum minus, currents cancel, zero output
voltage.
B/E) Only upper or lower switches on maximum, currents partially cancel, attenuated output voltage.
C/F) All switches on maximum and same polarity, all currents add, maximum output voltage.
In all 3 cases we have four resistors with value R in parallel and batteries are short circuit for AC. So
output impedance in all examples remains constant 0.25R regardless of switch position.
By changing the electronic switch settings we can have no voltage, half positive, full positive, half negative
and full negative output voltage.
In the practical converter we also have two converters for generating the output signal (matrix system).
This ensures that only the lowest bits have to change state around the zero crossing as each converter
starts at minimum or maximum and progresses up or down in small steps, not in the middle like with most
multi-bit DACs.
The lower bits are switched with R4R, the upper bits of each converter are split up in sub bits (fractal
system). This helps to further lower output impedance to 50 Ohms with given switch limitations, increase
accuracy and minimise glitches.
The end result is an accurate and clean multi-bit power DA converter with low enough output impedance
to directly drive the outputs. This way all lossy analogue circuits and related unavoidable degrading,
typically required for conventional DACs can be avoided.
4 17
/
© 1990-2023 - All Rights Reserved - ECdesigns
Advertisement
