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PCM54HP Fiches technique(PDF) 5 Page  BurrBrown (TI) 


PCM54HP Fiches technique(HTML) 5 Page  BurrBrown (TI) 
5 / 7 page ® PCM54/55 5 POWER SUPPLY SENSITIVITY Changes in the DC power supplies will affect accuracy. The PCM54 and PCM55 power supply sensitivity is shown by Figure 2. Normally, regulated power supplies with 1% or less ripple are recommended for use with the DAC. See also Power Supply Connections paragraph in the Installation and Operating Instructions section. SETTLING TIME Settling time is the total time (including slew time) required for the output to settle within an error band around its final value after a change in input (see Figure 3). Settling times are specified to ±0.006% of FSR; one for a large output voltage change of 3V and one for a 1LSB change. The 1LSB change is measured at the major carry (0111…11 to 10000.00), the point at which the worstcase settling time occurs. STABILITY WITH TIME AND TEMPERATURE The parameters of a D/A converter designed for audio applications should be stable over a relatively wide tempera ture range and over long periods of time to avoid undesirable periodic readjustment. The most important parameters are bipolar zero, differential linearity error, and total harmonic distortion. Most of the offset and gain drift with temperature or time is due to the drift of the internal reference zener diode. The PCM54 and PCM55 are designed so that these drifts are in opposite directions so that the bipolar zero voltage is virtually unaffected by variations in the reference voltage. Both DLE and THD are dependent upon the match ing and tracking of resistor ratios and upon VBE and hFE of the currentsource transistors. The PCM54 and PCM55 were designed so that any absolute shift in these components has virtually no effect on DLE or THD. The resistors are made of identical links of ultrastable nichrome thinfilm. The current density in these resistors is very low to further enhance their stability. DYNAMIC RANGE The dynamic range is a measure of the ratio of the smallest signals the converter can produce to the fullscale range and is usually expressed in decibels (dB). The theoretical dy namic range of a converter is approximately 6 x n, or about 96dB for a 16bit converter. The actual, or useful, dynamic range is limited by noise and linearity errors and is therefore somewhat less than the theoretical limit. However, this does point out that a resolution of at least 16 bits is required to obtain a 90dB minimum dynamic range, regardless of the accuracy of the converter. Another specification that is useful for audio applications is total harmonic distortion. TOTAL HARMONIC DISTORTION THD is useful in audio applications and is a measure of the magnitude and distribution of the linearity error, differential linearity error, and noise as well as quantization error. To be useful, THD should be specified for both high level and low level input signals. This error is unadjustable and is the most meaningful indicator of D/A converter accuracy for audio applications. The THD is defined as the ratio of the square root of the sum of the squares of the values of the harmonics to the value of the fundamental input frequency and is expressed in percent or dB. The rms value of the PCM54/55 error referred to the input can be shown to be: (1) where n is the number of samples in one cycle of any given sine wave, EL(i) is the linearity error of the PCM54 or PCM55 at each sampling point, and EQ(i) is the quantization 10.0 3.0 1.0 0.30 0.10 0.03 0.01 0.003 0.001 510 15 ±V CC Supplies (V) 0dB –60dB –20dB FIGURE 2. Effects of ±V CC on Total Harmonic Distortion (PCM54JP; VCCswithapproximately2%ripple). ε rms i n LQ n ii =+ = 1 1 2 Σ ΕΕ [( ) ( )] FIGURE 3. FullScale Range Settling Time vs Accuracy. 1.0 0.3 0.1 0.03 0.01 0.003 0.001 0.01 0.1 1.0 10.0 Settling Time ( µs) R L = 200Ω Current Output Mode Voltage Output Mode 
Numéro de pièce similaire  PCM54HP 

Description similaire  PCM54HP 


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