ATUC64L4U Atmel Corporation, ATUC64L4U Datasheet - Page 689

• Manufacturer Part Number: ATUC64L4U
• Manufacturer: Atmel Corporation

Specifications of ATUC64L4U

• Flash (kbytes): 64 Kbytes
• Pin Count: 48
• Max. Operating Frequency: 50 MHz
• Cpu: 32-bit AVR
• # Of Touch Channels: 17
• Hardware Qtouch Acquisition: Yes
• Max I/o Pins: 36
• Ext Interrupts: 36
• Usb Transceiver: 1
• Usb Speed: Full Speed
• Usb Interface: Device
• Spi: 1
• Twi (i2c): 2
• Uart: 4
• Lin: 4
• Ssc: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 12
• Adc Speed (ksps): 460
• Analog Comparators: 8
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 16
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: Yes
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.62 to 3.6
• Operating Voltage (vcc): 1.62 to 3.6
• Fpu: No
• Mpu / Mmu: Yes / No
• Timers: 6
• Output Compare Channels: 18
• Input Capture Channels: 12
• Pwm Channels: 35
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

28.6
28.6.1
28.6.1.1
28.6.1.2
28.6.1.3
28.6.2
32142A–12/2011
Functional Description
Construction
Initialization
CIC Interpolation Filter
Sigma Delta Modulator
Recreating the Analog Signal
The Audio Bitstream DAC is divided into several parts, the user interface, the signal processing
blocks, and the Sigma Delta modulator blocks. See
is used to configure the signal processing blocks and to input new data samples to the con-
verter.The signal processing blocks manages volume control, offset control, and upsampling.
The Sigma Delta blocks converts the parallel data to1-bit bitstreams.
The interpolation filter in the system is a Cascaded Integrator-Comb (CIC) interpolation filter
which interpolates from F
4th order CIC filter, and the basic building blocks of the filter is a comb part and an integrator
part. Since the CIC interpolator has a sinc-function frequency response it is compensated by a
linear phase CIC compensation filter to make the passband response more flat in the range 0-
20kHz, see figure
has the first zero at the input sampling frequency. This means that the first repeated specters
created by the upsampling process will not be fully rejected and the output signal will contain sig-
nals from these repeated specters. See
Since the human ear can not hear frequencies above 20kHz, we should not be affected by this
when the sample rate is above 40kHz, but digital measurement equipment will be affected. This
need to be accounted for when doing measurements on the system to prevent aliasing and
incorrect measurement results.
The Sigma Delta modulator is a 3rd order modulator consisting of three differentiators (delta
blocks), three integrators (sigma blocks), and a one bit quantizer. The purpose of the integrators
is to shape the noise, so that the noise is reduced in the audio passband and increased at the
higher frequencies, where it can be filtered out by an analog low-pass filter. To be able to filter
out all the noise at high frequencies the analog low-pass filter must be one order larger than the
Sigma Delta modulator.
Since the DAC and DACN outputs from the ABDAC are digital square wave signals, they have
to be passed through a low pass filter to recreate the analog signal. This also means that noise
on the IO voltage will couple through to the analog signal. To remove some of the IO noise the
ABDAC can output a clock signal, CLK, which can be used to resample the DAC and DACN sig-
nals on external Flip-Flops powered by a clean supply.
Before enabling the ABDACB the correct configuration must be applied to the Control Register
(CR). Configuring the Alternative Upsampling Ratio bit (CR.ALTUPR), Common Mode Offset
Control bit (CR.CMOC), and the Sampling Frequency field (CR.FS) according to the sampling
rate of the data that is converted and the type of amplifier the outputs are connected to is
required to get the correct behavior of the system. When the correct configuration is applied the
ABDACB can be enabled by writing a one to the Enable bit in the Control Register (CR.EN). The
module is disabled by writing a zero to the Enable bit. The module should be disabled before
entering sleep modes to ensure that the outputs are not left in an undesired state.
Figure 28-4 on page
s
to {125, 128, 136}xF
693. The frequency response of this type of interpolator
Figure 28-6 on page
s
depending on the control settings. This filter is a
Figure 28-1 on page
ATUC64/128/256L3/4U
694.
687. The user interface
689