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ML2258 データシート(PDF) 9 Page - Micro Linear Corporation |
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ML2258 データシート(HTML) 9 Page - Micro Linear Corporation |
9 / 12 page ML2258 9 Intermodulation Distortion With inputs consisting of sine waves at two frequencies, fA and fB, any active device with nonlinearities will create distortion products, of order (m+n), at sum and difference frequencies of mfA + nfB, where m, n = 0, 1, 2, 3,... . Intermodulation terms are those for which m or n is not equal to zero. The ML2258 (IMD) intermodulation distortion specification includes the second order terms (fA + fB) and (fA – fB) and the third order terms (2fA + fB), (2fA – fB), (fA + 2fB) and (fA – 2fB) only. 1.7 DIGITAL INTERFACE The analog inputs are selected by the digital addresses, ADDR0–ADDR2, and latched on the rising edge of ALE. This is described in the Multiplexer Addressing section. A conversion is initiated by the rising edge of a START pulse. As long as this pulse is high, the internal logic is reset. The sampling interval starts with the 4th CLK rising edge after a START falling edge and ends on the 8th rising edge of CLK, 4 CLK periods later. On the rising edge of the 8th CLK pulse, the conversion starts and EOC goes low. Each bit conversion in the successive approximation process takes 7 CLK periods. On the rising edge of the 64th CLK pulse, the digital output of the conversion is updated on the outputs DB0–DB7. On the rising edge of the 65th CLK pulse, EOC goes high indicating the conversion is done and data on DB0–DB7 is valid. One feature of the ML2258 over conventional devices is that the data is double-buffered. This means that the outputs DB0–DB7 will stay valid until updated at the end of the next conversion and will not become invalid when the next conversion starts. This facilitates interfacing with external logic of µP. The signal OE drives the data bus, DB0–DB7, into a high impedance state when held low. This allows the ML2258 to be tied directly to a µP system bus without any latches or buffers. 1.5 POWER SUPPLY AND REFERENCE DECOUPLING A 10µF electrolytic capacitor is recommended to bypass VCC to GND, using as short a lead length as possible. In addition, with clock frequencies above 1MHz, a 0.1µF ceramic disc capacitor should be used to bypass VCC to GND. If REF+ and REF– inputs are driven by long lines, they should be bypassed by 0.1µF Ceramic disc capacitors at the reference pins (pins 12, 16). 1.6 DYNAMIC PERFORMANCE Signal-to-Noise Ratio Signal-to-noise ratio (SNR) is the measured signal to noise at the output of the converter. The signal is the rms magnitude of the fundamental. Noise is the rms sum of all the nonfundamental signals up to half the sampling frequency. SNR is dependent on the number of quantization levels used in the digitization process; the more levels, the smaller the quantization noise. The theoretical SNR for a sine wave is given by SNR = (6.02N + 1.76)dB where N is the number of bits. Thus for ideal 8-bit converter, SNR = 49.92dB. Harmonic Distortion Harmonic distortion is the ratio of the rms sum of harmonics to the fundamental. Total harmonic distortion (THD) of the ML2258 is defined as THD VVV V V = ++ + 20 2 2 3 2 4 2 5 2 12 1 log / where V1 is the rms amplitude of the fundamental and V2, V3, V4, V5 are the rms amplitudes of the individual harmonics. |
同様の部品番号 - ML2258 |
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同様の説明 - ML2258 |
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