CS4270-CZZR Cirrus Logic Inc, CS4270-CZZR Datasheet - Page 28

• Manufacturer Part Number: CS4270-CZZR
• Description: 24-bit, 192kHz Stereo Codec
• Manufacturer: Cirrus Logic Inc

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5.4
5.4.1 Input Connections
The analog modulator samples the input at 6.144 MHz.The digital filter will reject signals within the stopband of the
filter. However, there is no rejection for input signals which are multiples of the input sampling frequency
(n
network. The capacitor values chosen not only provide the appropriate filtering of noise at the modulator sampling
frequency, but also act as a charge source for the internal sampling circuits. The use of capacitors which have a
large voltage coefficient (such as general purpose ceramics) must be avoided since these can degrade signal lin-
earity.
×
6.144 MHz), where n=0,1,2,... Refer to
Analog Connections
Three parameters determine the values of resistors R1 and R2 as shown in
attenuation, and input impedance. Source impedance is defined as the impedance as seen from the ADC
looking back into the signal network. Analog performance is optimized for small source impedance and a
source impedance above 2.5 kΩ results in degraded THD+N.
The required attenuation factor depends on the magnitude of the input signal. The full-scale input voltage
scales with VA; for VA = 5 V, the CS5344 full-scale input magnitude is 1 Vrms. R1 and R2 should be set
such that an input signal greater than the full-scale input should be attenuated to the appropriate magni-
tude. Typical line-level voltage in audio applications is 2 Vrms, in which case R1 and R2 must combine to
form an attenuation factor of 2, thus giving the CS5344 a 1 Vrms input.
Input impedance is the impedance from the signal source to the ADC analog input pins. The target input
impedance depends on the overall system specifications, but typical audio systems require an input im-
pedance of 10 kΩ.
illustrates an example configuration for a source impedance of 46 Ω, an attenuation factor of 1, and input
impedance of 9.8 kΩ.
Analog
Input
Table 6
Figure 12. CS4270 Recommended Analog Input Network
R1
Source Impedance
Attenuation Factor
Table 6. Analog Input Design Parameters
shows the input parameters and the associated design equations.
Input Impedance
Figure 12
R2
which shows the recommended topology of the analog input
10 µF
(
------------------------ -
(
R1 R2
R1
R1
------------------- -
R1 R2
R2
×
+
+
2200 pF
×
R2
R2
)
)
AINx
CS4270
Figure
12: source impedance,
CS4270
DS686A1
Figure 13