Electronic Components Datasheet Search |
|
AD7884 Datasheet(PDF) 8 Page - Analog Devices |
|
AD7884 Datasheet(HTML) 8 Page - Analog Devices |
8 / 16 page REV. E AD7884/AD7885 –8– TERMINOLOGY Integral Nonlinearity This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. Differential Nonlinearity This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Bipolar Zero Error This is the deviation of the midscale transition (all 0s to all 1s) from the ideal (AGND). Positive Gain Error This is the deviation of the last code transition (01 . . . 110 to 01 . . . 111) from the ideal (+VREF+S – 1 LSB) after bipolar zero error has been adjusted out. Negative Gain Error This is the deviation of the first code transition (10 . . . 000 to 10 . . . 001) from the ideal (–VREF+S + 1 LSB) after bipolar zero error has been adjusted out. Signal-to-(Noise + Distortion) Ratio This is the measured ratio of signal-to-(noise + distortion) at the output of the A/D converter. The signal is the rms amplitude of the fundamental. Noise is the rms sum of all nonfundamental signals up to half the sampling frequency (fS/2), excluding dc. The ratio is dependent upon the number of quantization levels in the digitization process; the more levels, the smaller the quan- tization noise. The theoretical signal-to-(noise + distortion) ratio for an ideal N-bit converter with a sine wave input is given by Signal to Noise Distortion N dB −− + () =+ () 602 1 76 .. Thus for an ideal 16-bit converter, this is 98 dB. Total Harmonic Distortion Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7884/AD7885, it is defined as THD dB VVV V V V () log = ++ + + 20 2 2 3 2 4 2 5 2 6 2 1 where V1 is the rms amplitude of the fundamental and V2, V3, V4, V5, and V6 are the rms amplitudes of the second through the sixth harmonics. Peak Harmonic or Spurious Noise Peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the ADC output spectrum (up to fS/2 and excluding dc) to the rms value of the fundamental. Normally, the value of this specification is determined by the larg- est harmonic in the spectrum, but for parts where the harmonics are buried in the noise floor, it will be a noise peak. Intermodulation Distortion With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities will create distortion products at sum and difference frequencies of mfa ± nfb where m, n = 0, 1, 2, 3, and so on. Intermodulation terms are those for which neither m nor n are equal to zero. For example, the second order terms include (fa + fb) and (fa – fb), while the third order terms include (2fa + fb), (2fa – fb), (fa + 2fb), and (fa – 2fb). The AD7884/AD7885 is tested using the CCIFF standard where two input frequencies near the top end of the input bandwidth are used. In this case, the second and third order terms are of different significance. The second order terms are usually distanced in frequency from the original sine waves while the third order terms are usually at a frequency close to the input frequencies. As a result, the second and third order terms are specified separately. The calculation of the intermodulation distortion is as per the THD specification, where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the fundamental expressed in dB. Power Supply Rejection Ratio This is the ratio of the change in positive gain error to the change in VDD or VSS, in dB. It is a dc measurement. OPERATIONAL DIAGRAM An operational diagram for the AD7884/AD7885 is shown in Figure 6. It is set up for an analog input range of ±5 V. If a ±3 V input range is required, A1 should drive ±3V INS and ±3V INF with ±5VINS, ±5VINF being tied to system AGND. 3VINF 5VINF –5V +5V AD711, AD845, OR AD817 AD817 AGNDS AGNDF AD7884/ AD7885 AD845, AD817, OR EQUIVALENT NOTE: POWER SUPPLY DECOUPLING NOT SHOWN GND DGND VDD = +5V CONTROL INPUTS VINV VREF+S VREF+F VREF– 3VINS 5VINS AVSS VDD AVDD VSS VIN AD780 2 6 8 4 10 F A1 A2 A3 A4 DATA OUTPUTS AD845, AD817, OR EQUIVALENT Figure 6. AD7884/AD7885 Operational Diagram The chosen input buffer amplifier (A1) should have low noise and distortion and fast settling time for high bandwidth applications. The AD711, AD845, and AD817 are suitable op amps. A2 is the force, sense amplifier for AGND. The AGNDS pin should be at zero potential. Therefore, the amplifier must have a low input offset voltage and good noise performance. It must also have the ability to deal with fast current transients on the AGNDS pin. The AD817 has the required performance and is the recommended amplifier. If AGNDS and AGNDF are simply tied together to star ground instead of buffering, the SNR and THD are not signifi- cantly degraded. However, dc specifications like INL, bipolar zero, and gain error will be degraded. |
Similar Part No. - AD7884_15 |
|
Similar Description - AD7884_15 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |