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821024 Datasheet(PDF) 5 Page - Integrated Device Technology |
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821024 Datasheet(HTML) 5 Page - Integrated Device Technology |
5 / 14 page REVISION A 06/25/14 821024 DATA SHEET 5 QUAD NON-PROGRAMMABLE PCM CODEC FUNCTIONAL DESCRIPTION The IDT821024 contains four channel PCM CODEC with on chip digital filters. It provides the four-wire solution for the subscriber line circuitry in digital switches. The device converts analog voice signal to digital PCM data, and converts digital PCM data back to analog signal. Digital filters are used to bandlimit the voice signals during the conversion. Either A-law or μ-law is supported by the IDT821024. The law selection is performed by A/μ pin. The frequency of the master clock (MCLK) can be 2.048 MHz, 4.096 MHz, or 8.192 MHz. Internal circuitry determines the master clock frequency automatically. The serial PCM data for four channels are time multiplexed via two pins, DX and DR. The time slots of the four channels are determined by the individual Frame Sync signals at rates from 256 kHz to 8.192 MHz. For each channel, the IDT821024 provides a transmit Frame Sync signal and a receive Frame Sync signal. Each channel of the IDT821024 can be powered down independently to save power consumption. The Channel Power Down Pins PDN1-4 configure channels to be active (power-on) or standby (power-down) separately. Signal Processing High performance oversampling Analog-to-Digital Converters (ADC) and Digital-to-Analog Converters (DAC) are used in the IDT821024 to provide the required conversion accuracy. The associated decimation and interpo- lation filtering are realized with both dedicated hardware and Digital Signal Processor (DSP). The DSP also handles all other necessary functions such as PCM bandpass filtering and sample rate conversion. Transmit Signal Processing In the transmit path, the analog input signal is received by the ADC and converted into digital data. The digital output of the oversampling ADC is decimated and sent to the DSP. The transmit filter is implemented in the DSP as a digital bandpass filter. The filtered signal is further decimated and compressed to PCM format. Transmit PCM Interface The transmit PCM interface clocks out 1 byte (8 bits) PCM data out of DX pin every 125 μs. The transmit logic, synchronized by the Transmit Frame Sync signal (FSXn), controls the data transmission. The FSXn pulse identifies the transmit time slot of the PCM frame for Channel N. The PCM Data is transmitted serially on DX pin with the Most Significant Bit (MSB) first. When the PCM data is being output on DX pin, the TSC signal will be pulled low. Receive Signal Processing In the receive path, the PCM code is received at the rate of 8,000 samples per second. The PCM code is expanded and sent to the DSP for interpolation. A receive filter is implemented in the DSP as a digital lowpass filter. The filtered signal is then sent to an oversampling DAC. The DAC output is post-filtered and delivered at VOUT pin by an amplifier. The amplifier can drive resistive load higher than 2 K Ω. Receive PCM Interface The receive PCM interface clocks 1 byte (8 bits) PCM data into DR pin every 125 μs. The receive logic, synchronized by the Receive Frame Sync signal (FSRn), controls the data receiving process. The FSRn pulse identifies the receive time slot of the PCM frame for Channel N. The PCM Data is received serially on DR pin with the Most Significant Bit (MSB) first. Hardware Gain Setting In Transmit Path The transmit gain of the IDT821024 for each channel can be set by 2 resistors, R REF and RTXn (as shown in Figure 1), according to the following equation: The receive gain of IDT821024 is fixed and equal to 1. Figure 1. IDT821024 Transmit Gain Setting for Channel 1 |
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