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AD1865N Scheda tecnica(PDF) 4 Page - Analog Devices |
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AD1865N Scheda tecnica(HTML) 4 Page - Analog Devices |
4 / 12 page AD1865 REV. 0 –4– TOTAL HARMONIC DISTORTION + NOISE Total harmonic distortion plus noise (THD+N) is defined as the ratio of the square root of the sum of the squares of the am- plitudes of the harmonics and noise to the value of the funda- mental input frequency. It is usually expressed in percent. THD+N is a measure of the magnitude and distribution of lin- earity error, differential linearity error, quantization error and noise. The distribution of these errors may be different, depend- ing on the amplitude of the output signal. Therefore, to be most useful, THD+N should be specified for both large (0 dB) and small (–20 dB, –60 dB) signal amplitudes. THD+N measure- ments for the AD1865 are made using the first 19 harmonics and noise out to 30 kHz. SIGNAL-TO-NOISE RATIO The signal-to-noise ratio is defined as the ratio of the amplitude of the output when a full-scale code is entered to the amplitude of the output when a midscale code is entered. It is measured using a standard A-Weight filter. SNR for the AD1865 is mea- sured for noise components out to 30 kHz. CHANNEL SEPARATION Channel separation is defined as the ratio of the amplitude of a full-scale signal appearing on one channel to the amplitude of that same signal which couples onto the adjacent channel. It is usually expressed in dB. For the AD1865 channel separation is measured in accordance with EIAJ Standard CP-307, Section 5.5. D-RANGE DISTORTION D-Range distortion is equal to the value of the total harmonic distortion + noise (THD+N) plus 60 dB when a signal level of –60 dB below full scale is reproduced. D-Range is tested with a 1 kHz input sine wave. This is measured with a standard A-Weight filter as specified by EIAJ Standard CP-307. GAIN ERROR The gain error specification indicates how closely the output of a given channel matches the ideal output for given input data. It is expressed in % of FSR and is measured with a full-scale out- put signal. INTERCHANNEL GAIN MATCHING The gain matching specification indicates how closely the ampli- tudes of the output signals match when producing identical in- put data. It is expressed in % of FSR (Full-Scale Range = 6 V for the AD1865) and is measured with full-scale output signals. MIDSCALE ERROR Midscale error is the deviation of the actual analog output of a given channel from the ideal output (0 V) when the twos complement input code representing half scale is loaded into the input register of the DAC. It is expressed in mV and is mea- sured with half-scale output signals. INTERCHANNEL MIDSCALE MATCHING The midscale matching specification indicates how closely the amplitudes of the output signals of the two channels match when the twos complement input code representing half scale is loaded into the input register of both channels. It is expressed in mV and is measured with half-scale output signals. FUNCTIONAL DESCRIPTION The AD1865 is a complete, monolithic, dual 18-bit audio DAC. No external components are required for operation. As shown in the block diagram, each chip contains two voltage references, two output amplifiers, two 18-bit serial input registers and two 18-bit DACs. The voltage reference section provides a reference voltage for each DAC circuit. These voltages are produced by low-noise bandgap circuits. Buffer amplifiers are also included. This com- bination of elements produces reference voltages that are unaf- fected by changes in temperature and age. The output amplifiers use both MOS and bipolar devices and incorporate an all NPN output stage. This design technique produces higher slew rate and lower distortion than previous techniques. Frequency response is also improved. When com- bined with the appropriate on-chip feedback resistor, the output op amps convert the output current to output voltages. The 18-bit D/A converters use a combination of segmented de- coder and R-2R architecture to achieve consistent linearity and differential linearity. The resistors which form the ladder struc- ture are fabricated with silicon chromium thin film. Laser trim- ming of these resistors further reduces linearity errors resulting in low output distortion. The input registers are fabricated with CMOS logic gates. These gates allow the achievement of fast switching speeds and low power consumption, contributing to the low glitch and low power dissipation of the AD1865. 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 AD1865 +VS NC TRIM MSB SJ DL LL DGND AGND VOUT IOUT RF –VS IOUT +VL VOUT TRIM MSB LR CLK DR AGND SJ RF 18-BIT LATCH 18-BIT D/A REFERENCE 18-BIT LATCH 18-BIT D/A REFERENCE NC = NO CONNECT AD1865 Block Diagram (DIP Package) |
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