MT-017 Datasheet, PDF (5/7 Pages) Analog Devices – Oversampling Interpolating DACs

MT-017
N-BITS @ f_s
(A) SINGLE BIT
N-BITS @ K f_s
1- BIT @ Kf_S
DIGITAL
INTERPOLATION
FILTER
DIGITAL
ΣΔ
MODULATOR
ANALOG SIGNAL:
2 LEVELS
1-BIT
DAC
ANALOG
OUTPUT
FILTER
ANALOG
OUTPUT
N-BITS @ f_s
(B) MULTIBIT
N-BITS @ K f_s
M- BITS @ Kf_S
DIGITAL
INTERPOLATION
FILTER
DIGITAL
MULTIBIT
ΣΔ
MODULATOR
ANALOG SIGNAL:
2^M LEVELS
M-BIT
DAC
ANALOG
OUTPUT
FILTER
ANALOG
OUTPUT
Figure 5: Sigma-Delta DACs
It is possible to use more than one bit in the Σ-Δ DAC, and this leads to the multibit architecture
shown in Figure 5B. The concept is similar to that of interpolating DACs previously discussed,
with the addition of the digital sigma-delta modulator.
In the past, multibit DACs have been difficult to design because of the accuracy requirement on
the n-bit internal DAC (this DAC, although only n-bits, must have the linearity of the final
number of bits, N). The AD195x-series of audio DACs, however use a proprietary data
scrambling technique (called data directed scrambling) which overcomes this problem and
produces excellent performance with respect to all audio specifications.
The AD1955 multibit sigma-delta audio DAC is shown in Figure 6. The AD1955 also uses data
directed scrambling, supports a multitude of DVD audio formats and has an extremely flexible
serial port. THD + N is typically 110 dB.
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