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CS5330A-BS Arkusz danych(PDF) 10 Page - Cirrus Logic |
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CS5330A-BS Arkusz danych(HTML) 10 Page - Cirrus Logic |
10 / 30 page Analog Connections Figure 1 shows the analog input connections. The analog inputs are presented to the modula- tors via the AINR and AINL pins. Each analog input will accept a maximum of 4 Vpp centered at +2.4 V. The CS5330A/31A samples the analog inputs at 128 × Fs, 6.144 MHz for a 48 kHz sample-rate. The digital filter rejects all noise above 29 kHz except for frequencies right around 6.144 MHz ± 21.7 kHz (and multiples of 6.144 MHz). Most audio signals do not have significant energy at 6.144 MHz. Nevertheless, a 150 Ω resistor in se- ries with each analog input and a 10 nF capacitor across the inputs will attenuate any noise energy at 6.144 MHz, in addition to pro- viding the optimum source impedance for the modulators. The use of capacitors which have a large voltage coefficient must be avoided since these will degrade signal linearity. It is also im- portant that the self-resonant frequency of the capacitor be well above the modulator sampling frequency. General purpose ceramics and film capacitors do not meet these requirements. How- ever, NPO and COG capacitors are acceptable. If active circuitry precedes the ADC, it is recom- mended that the above RC filter is placed between the active circuitry and the AINR and AINL pins. The above example frequencies scale linearly with Fs. High Pass Filter The operational amplifiers in the input circuitry driving the CS5330A/31A may generate a small DC offset into the A/D converter. The CS5330A/31A includes a high pass filter after the decimator to remove any DC offset which could result in recording a DC level, possibly yielding "clicks" when switching between de- vices in a multichannel system. The characteristics of this first-order high pass filter are outlined below for Fs equal 48 kHz. This filter response scales linearly with sample rate. Frequency response:-3 dB @ 3.7 Hz -0.1 dB @ 20 Hz Phase deviation:10 degrees @ 20 Hz Passband ripple:None Initialization and Power-Down The Initialization and Power-Down sequence is shown in Figure 4. Upon initial power-up, the digital filters and delta-sigma modulators are re- set and the internal voltage reference is powered down. The device will remain in the Initial Power-Down mode until MCLK is presented. Once MCLK is available, the CS5330A/31A will make a master/slave mode decision based upon the presence/absence of a 47 kohm pull-down re- sistor on SDATA as shown in Figure 1. The master/slave decision is made during initial power-up as shown in Figure 4. In master mode, SCLK and LRCK are outputs where the MCLK / LRCK frequency ratio is 256 ×. LRCK will appear as an output 127 MCLK cycles into the initialization sequence. At this time, power is applied to the internal voltage reference and the analog inputs will move to ap- proximately 2.4 Volts. SDATA is static low during the initialization and high pass filter set- tling sequence, which requires 11,265 LRCK cycles (235 ms at a 48 kHz output sample rate). In slave mode, SCLK and LRCK are inputs where the MCLK / LRCK frequency ratio must be either 256 ×, 384× or 512×. Once the MCLK and LRCK are detected, MCLK occurrences are counted over one LRCK period to determine the MCLK / LRCK frequency ratio. At this time, power is applied to the internal voltage reference and the analog inputs will move to approxi- mately 2.4 Volts. SDATA is static high during the initialization and high pass filter settling se- quence, which requires 11,265 LRCK cycles (235 ms at a 48 kHz sample rate). CS5330A/CS5331A 10 DS138F2 |
Podobny numer części - CS5330A-BS |
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Podobny opis - CS5330A-BS |
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