Datasheet LTC1407-1, LTC1407A-1 (Analog Devices) - 13

LTC1407-1/LTC1407A-1
APPLICATIONS INFORMATION DRIVING THE ANALOG INPUT
the time between conversions. The best choice for an op amp to drive the LTC1407-1/LTC1407A-1 depends on the The differential analog inputs of the LTC1407-1/LTC1407A-1 application. Generally, applications fall into two categories: are easy to drive. The inputs may be driven differentially or AC applications where dynamic specifi cations are most as a single-ended input (i.e., the CH0– input is AC grounded critical and time domain applications where DC accuracy at VCC/2). All four analog inputs of both differential analog and settling time are most critical. The following list is a input pairs, CH0+ with CH0– and CH1+ with CH1–, are summary of the op amps that are suitable for driving the sampled at the same instant. Any unwanted signal that is LTC1407-1/LTC1407A-1. common to both inputs of each input pair will be reduced by the common mode rejection of the sample-and-hold circuit.
LTC1566-1:
Low Noise 2.3MHz Continuous Time Low- The inputs draw only one small current spike while charging pass Filter. the sample-and-hold capacitors at the end of conversion.
LT
®
1630:
Dual 30MHz Rail-to-Rail Voltage FB Amplifi er. During conversion, the analog inputs draw only a small 2.7V to ±15V supplies. Very high A leakage current. If the source impedance of the driving VOL, 500μV offset and 520ns settling to 0.5LSB for a 4V swing. THD and noise circuit is low, then the LTC1407-1/LTC1407A-1 inputs can are – 93dB to 40kHz and below 1LSB to 320kHz (A be driven directly. As source impedance increases, so will V = 1, 2V acquisition time. For minimum acquisition time with high P-P into 1kΩ, VS = 5V), making the part excellent for AC applications (to 1/3 Nyquist) where rail-to-rail perfor- source impedance, a buffer amplifi er must be used. The mance is desired. Quad version is available as LT1631. main requirement is that the amplifi er driving the analog input(s) must settle after the small current spike before
LT1632:
Dual 45MHz Rail-to-Rail Voltage FB Amplifi er. the next conversion starts (settling time must be 39ns for 2.7V to ±15V supplies. Very high AVOL, 1.5mV offset and full throughput rate). Also keep in mind, while choosing 400ns settling to 0.5LSB for a 4V swing. It is suitable for an input amplifi er, the amount of noise and harmonic applications with a single 5V supply. THD and noise are distortion added by the amplifi er. – 93dB to 40kHz and below 1LSB to 800kHz (AV = 1, 2VP-P into 1kΩ, VS = 5V), making the part excellent for AC applications where rail-to-rail performance is desired.
CHOOSING AN INPUT AMPLIFIER
Quad version is available as LT1633. Choosing an input amplifi er is easy if a few requirements
LT1801:
80MHz GBWP, –75dBc at 500kHz, 2mA/ampli- are taken into consideration. First, to limit the magnitude fi er, 8.5nV/√Hz. of the voltage spike seen by the amplifi er from charging the sampling capacitor, choose an amplifi er that has a low
LT1806/LT1807:
325MHz GBWP, –80dBc distortion at output impedance (<100Ω) at the closed-loop bandwidth 5MHz, unity-gain stable, rail-to-rail in and out, 10mA/am- frequency. For example, if an amplifi er is used in a gain plifi er, 3.5nV/√Hz. of 1 and has a unity-gain bandwidth of 50MHz, then the
LT1810:
180MHz GBWP, –90dBc distortion at 5MHz, output impedance at 50MHz must be less than 100Ω. The unity-gain stable, rail-to-rail in and out, 15mA/amplifi er, second requirement is that the closed-loop bandwidth must 16nV/√Hz. be greater than 40MHz to ensure adequate small-signal settling for full throughput rate. If slower op amps are LinearView is a trademark of Linear Technology Corporation. used, more time for settling can be provided by increasing 14071fb 13