ANALOG DEVICES AN-222 数据手册说明书.pdf

ANALOG AN-222 DEVICES APPLICATION NOTE by Matt Smith Single rail power supplies are the normal Source of AD7569 contains an internal voltage Teference，8a power for the electronics in many disk drive circuits. For samplehold amplifier，an 8-bit ADC，an 8-bit DAC, a a typical application such as head positioning, the sen- buffer amplifier plus all the digital control circuitry, The AD7669 is similar with the addition of an extra 8-bit DAC. sor and control signals are often referenced to a voltage Both parts may be operated from a single 5V power above ground potential. This is done in order to ensure that both the signal conditioning and the control cif- supply with 8 choice of 0 to 1.25V or 0 to 2.5V signal cuitry is operating within its linear region. With any lin- ranges for both the ADC and the DAC. For further infer ear circuitry, such as op amps, there must be sufficient mation on both parts consult the data sheet. headroom between the signal extremes and the power To accommodate input signals which are not referenced supplies in order to maintain linear operation over the to 0Vbut to some offset voltage, VorFsET' it is necesSary entire signal range. With single supply linear circuitry, to bias the ground of the ADC, AGNDabpc, with the same there must be sufficient headroom between the mini- voltage offeet， This ensures that no unused codes or mum signal level and ground for the same reason. TO deadband wiil exist at the bottom of the ADC code table. achieve this, the linear circuitry is often operated with an Additionally in orde