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AD1870 数据表(PDF) 7 Page - Analog Devices |
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AD1870 数据表(HTML) 7 Page - Analog Devices |
7 / 20 page AD1870 REV. A –7– (Continued from Page 1 ) The flexible serial output port produces data in two’s complement, MSB-first format. The input and output signals are TTL compatible. The port is configured by pin selections. Each 16-bit output word of a stereo pair can be formatted within a 32-bit field of a 64-bit frame as either right-justified, I 2S compatible, word clock controlled, or left-justified positions. Both 16-bit samples can also be packed into a 32-bit frame, in left-justified and I 2S compatible positions. The AD1870 is fabricated on a single monolithic integrated circuit using a 0.5 µm CMOS double polysilicon, double metal process and is offered in a plastic 28-lead SOIC package. Analog and digital supply connections are separated to isolate the analog circuitry from the digital supply and reduce digital crosstalk. The AD1870 operates from a single 5 V power supply over the temperature range of –40 °C to +85°C and typically consumes less than 260 mW of power. THEORY OF OPERATION - Modulator Noise Shaping The stereo, internally differential, analog modulator of the AD1870 employs a proprietary feedforward and feedback archi- tecture that passes input signals in the audio band with a unity transfer function yet simultaneously shapes the quantization noise generated by the one-bit comparator out of the audio band (see Figure 1). Without the - architecture, this quanti- zation noise would be spread uniformly from dc to one-half the oversampling frequency, 64 × fS. DAC DAC SINGLE-TO- DIFFERENTIAL CONVERTER MODULATOR BITSTREAM OUTPUT VIN VIN VIN Figure 1. Modulator Noise Shaper (One Channel) - architectures “shape” the quantization noise-transfer function in a nonuniform manner. Through careful design, this transfer function can be specified to high-pass filter the quantization noise out of the audio band into higher frequency regions. The AD1870 also incorporates a feedback resonator from the fourth integrator’s output to the third integrator’s input. This resona- tor does not affect the signal transfer function but allows the flexible placement of a zero in the noise transfer function for more effective noise shaping. Oversampling by 64 simplifies the implementation of a high performance audio analog-to-digital conversion system. Antialias requirements are minimal; a single pole of filtering will usually suffice to eliminate inputs near fS and its higher multiples. A fourth order architecture was chosen both to strongly shape the noise out of the audio band and to help break up the idle tones produced in all - architectures. These architectures have a tendency to generate periodic patterns with a constant dc input, a response that looks like a tone in the frequency domain. These idle tones have a direct frequency dependence on the input dc offset and an indirect dependence on temperature and time as it affects the dc offset. The AD1870 suppresses idle tones 20 dB or better below the integrated noise floor. The AD1870’s modulator was designed, simulated, and ex- haustively tested to remain stable for any input within a wide tolerance of its rated input range. The AD1870 is designed to internally reset itself should it ever be overdriven, to prevent it from going unstable. It will reset itself within 5 µs at a 48 kHz sampling frequency after being overdriven. Overdriving the inputs will produce a waveform “clipped” to plus or minus full scale. See TPCs 1 through 6 for illustrations of the AD1870’s typical analog performance as measured by an Audio Precision System One. Signal-to-(distortion + noise) is shown under a range of conditions. Note that there is a small variance between the AD1870 analog performance specifications and some of the performance plots. This is because the Audio Precision System One measures THD and noise over a 20 Hz to 24 kHz band- width, while the analog performance is specified over a 20 Hz to 20 kHz bandwidth (i.e., the AD1870 performs slightly better than the plots indicate). The power supply rejection graph (TPC 5) illustrates the benefits of the AD1870’s internal differential ar- chitecture. The excellent channel separation shown in TPC 6 is the result of careful chip design and layout. Digital Filter Characteristics The digital decimator accepts the modulator’s stereo bit stream and simultaneously performs two operations on it. First, the decimator low-pass filters the quantization noise that the modu- lator shaped to high frequencies and filters any other out-of- audio-band input signals. Second, it reduces the data rate to an output word rate equal to fS. The high frequency bit stream is decimated to stereo 16-bit words at 48 kHz (or other desired fS). The out-of-band one-bit quantization noise and other high frequency components of the bit stream are attenuated by at least 90 dB. The AD1870 decimator implements a symmetric finite impulse response (FIR) filter that possesses a linear phase response. This filter achieves a narrow transition band (0.1 × f S), high stop-band attenuation (>90 dB), and low pass-band ripple (<0.006 dB). The narrow transition band allows the unattenu- ated digitization of 20 kHz input signals with fS as low as 0 –80 1.0 –60 –70 0.1 0.0 –40 –50 –30 –20 –10 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 –110 –90 –100 NORMALIZED f S –120 10 TPC 7. Digital Filter Signal Transfer Function to fS |
类似零件编号 - AD1870 |
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类似说明 - AD1870 |
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