Agilent Technologies 93000 SOC Series Training Manual page 295

CODEC = Voice Coder/
Decoder
Linear vs. Non-Linear Converters
This training concentrates on linear DACs and ADCs. Of course,
there are also non-linear DACs and ADCs.
Discrete digital
output values
–
Analog input
voltage
Linear ADC
Linear and Non-Linear ADC
CODECs for voice transmission via telephone lines, for example,
often use non-linear ADCs and DACs. They save bits by
considering the properties of speech signals and the human ear.
It should be mentioned that before you start testing a DAC or
ADC, you need to know and consider its transfer characteristics.
Flash ADC Operating Principle
A Flash ADC provides very fast analog-to-digital conversion. A n-
bit Flash ADC has at least 2
simultaneously applied to all these comparators. The reference
voltage for each comparator is derived from a string of resistor
voltage dividers. The reference voltage for each comparator is 1
LSB higher than that of the comparator below. An ADC of this
type, especially with a high resolution (n >12) requires a very
precise and stable reference voltage.
Lesson 1 – The Training ADC
Discrete digital
output values
+ –
Non-linear ADC
n
-1 comparators. The analog input is
+
Analog input
voltage
295