Digital Signal Processing Reference
In-Depth Information
Delta-modulator
+
-
+
+
Digital
transmission
TP
S&H
1 Bit ADC
Integrator
analog
analog
+
T
A
T
A
Sigma-Delta-
modulated signal
Integrator
Integrator
+
-
Digital
transmission
+
+
TP
S&H
1 Bit ADC
analog
analog
T
A
Sigma-Delta-Modulator/-Encoder
Recorder
Noise
S& H
Di fference
Addi tion
Delay 1
Delay 2
1-Bit-ADC
sym. level
LP 1
LP 2
3
Difference signal (channel 2)
2
Output of Integrator (channel 3)
1
0
Recovered signal (channel 5)
-1
Audio signal and sample &hold (channel 0 and 1)
Sigma-Delta-encoded signal (channel 4)
-2
-3
16:03:00,0
16:03:00,5
16:03:01,0
16:03:01,5
16:03:02,0
16:03:02,5
16:03:03,0
16:03:03,5
16:03:04,0
16:03:04,5
16:03:05,0
16:03:05,5
16:03:06,0
16:03:06,5
16:03:07,0
h:mi n:s
Illustration 230:
From delta modulator to sigma-delta modulator
The form of integrator used here results from the DASYLab circuit in Illustration 228 and Illustration 229:
an adder which adds the last output value of the 1 bit ADC to the next input value. If an integrator of this
kind is connected additionally before the delta-modulator it can be done without in the receiver. The circuit
below in which the the two integrators (in actual fact, the adder, for which the Greek letter
(sigma) is
used) are replaced by a single integrator before the 1 bit ADC is then equivalent. This circuit is therefore
called a
Σ
Σ−Δ−
modulator/encoder.
By means of this process of re-arrangement from the receiver to the transmitter numerous other advan-
tages are achieved which are described in more detail in the text. As a result of these advantages the
Σ−Δ−
modulator/converter has become a kind of standard ADC for high-quality A/D conversion (audio,
measuring technology).
