データシートサーチシステム |
|
AD7870AJN データシート(PDF) 6 Page - Analog Devices |
|
AD7870AJN データシート(HTML) 6 Page - Analog Devices |
6 / 12 page AD7870A –6– REV. 0 CONVERTER DETAILS The AD7870A is a complete 12-bit A/D converter, requiring no external components apart from power supply decoupling ca- pacitors. It is comprised of a 12-bit successive approximation ADC based on a fast settling voltage-output DAC, a high speed comparator and SAR, a track/hold amplifier, a 3 V buried Zener reference, a clock oscillator and control logic. INTERNAL REFERENCE The AD7870A has an on-chip temperature compensated buried Zener reference that is factory trimmed to 3 V ± 10 mV. In- ternally it provides both the DAC reference and the dc bias re- quired for bipolar operation. The reference output is available (REF OUT) and capable of providing up to 500 µA to an ex- ternal load. The maximum recommended capacitance on REF OUT for normal operation is 50 pF. If the reference is required for use external to the AD7870A, it should be decoupled with a 200 Ω resistor in series with a parallel combination of a 10 µF tantalum capacitor and a 0.1 µF ceramic capacitor. These decoupling components are required to remove voltage spikes caused by the AD7870A’s internal operation. Figure 3. Reference Circuit TRACK-AND-HOLD AMPLIFIER The track-and-hold amplifier on the analog input of the AD7870A allows the ADC to accurately convert an input sine wave of 6 V peak-peak amplitude to 12-bit accuracy. The input bandwidth of the track/hold amplifier is much greater than the Nyquist rate of the ADC even when the ADC is operated at its maximum throughput rate. The 0.1 dB cutoff frequency occurs typically at 500 kHz. The track/hold amplifier acquires an input signal to 12-bit accuracy in less than 2 µs. The overall throughput rate is equal to the conversion time plus the track/hold amplifier ac- quisition time. For a 2.5 MHz input clock the throughput rate is 10 µs max. The operation of the track/hold is essentially transparent to the user. The track/hold amplifier goes from its tracking mode to its hold mode at the start of conversion. The track-to-hold transi- tion occurs on the falling edge of CONVST. Figure 4. Analog Input ANALOG INPUT Figure 4 shows the AD7870A analog input. The analog input range is ±3 V into an input resistance of typically 15 kΩ. The designed code transitions occur midway between successive integer LSB values (i.e., 1/2 LSB, 3/2 LSBs, 5/2 LSBs . . . FS 3/2 LSBs). The output code is twos complement binary with 1 LSB = FS/4096 = 6 V/4096 = 1.46 mV. The ideal input/out- put transfer function is shown in Figure 5. Figure 5. Bipolar Input/Output Transfer Function BIPOLAR OFFSET AND FULL SCALE ADJUSTMENT In most digital signal processing (DSP) applications, offset and full-scale errors have little or no effect on system performance. Offset error can always be eliminated in the analog domain by ac coupling. Full-scale error effect is linear and does not cause problems as long as the input signal is within the full dynamic range of the ADC. Some applications will require that the input signal span the full analog input dynamic range. In such applica- tions, offset and full-scale error will have to be adjusted to zero. Where adjustment is required, offset error must be adjusted be- fore full-scale error. This is achieved by trimming the offset of the op amp driving the analog input of the AD7870A while the input voltage is 1/2 LSB below ground. The trim procedure is as follows: apply a voltage of 0.73 mV (–1/2 LSB) at V1 in Figure 6 and adjust the op amp offset voltage until the ADC output code flickers between 1111 1111 1111 and 0000 0000 0000. Gain error can be adjusted at either the first code transition (ADC negative full scale) or the last code transition (ADC positive full scale). The trim procedures for both cases are as follows (see Figure 6). |
同様の部品番号 - AD7870AJN |
|
同様の説明 - AD7870AJN |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト 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 |