AD781–SPECIFICATIONS DC SPECIFICATIONS (TMIN to TMAX, VCC = +12 V 6 10%, VEE = –12 V 6 10%, CL = 20 pF, unless otherwise noted) Parameter Min AD781J Typ SAMPLING CHARACTERISTICS Acquisition Time 10 V Step to 0.01% 10 V Step to 0.1% Small Signal Bandwidth Full Power Bandwidth HOLD CHARACTERISTICS Effective Aperture Delay (25°C) Aperture Jitter (25°C) Hold Settling (to 1 mV, 25°C) Droop Rate Feedthrough (25°C) (VIN = ± 5 V, 100 kHz) –35 Max 600 500 4 1 700 600 –25 50 250 0.
AD781 (TMIN to TMAX, VCC = +12 V 6 10%, VEE = –12 V 6 10%, CL = 20 pF, unless otherwise noted)1 HOLD MODE AC SPECIFICATIONS Parameter Min AD781J Typ TOTAL HARMONIC DISTORTION FIN = 10 kHz FIN = 50 kHz FIN = 100 kHz –90 –73 –68 SIGNAL-TO-NOISE AND DISTORTION FIN = 10 kHz 72 FIN = 50 kHz FIN = 100 kHz 78 73 67 INTERMODULATION DISTORTION FIN1 = 49 kHz, FIN2 = 50 kHz 2nd Order Products 3rd Order Products –77 –78 Max Min –80 AD781A Typ Max –90 –73 –68 72 Min –80 78 73 67 AD781S Typ –90 –73 –68
AD781 80 EFFECTIVE APERTURE DELAY – ns 70 V+ 1.0 DROOP RATE – µV/µs 60 PSRR – dB –10 10.0 50 V– 40 30 20 0.1 0.01 10 0 0.001 1 100 10 1k 10k 100k 0 1M 25 50 75 100 125 –15 –20 –25 –30 100 150 1k TEMPERATURE – °C FREQUENCY – Hz Power Supply Rejection Ratio vs. Frequency Droop Rate vs. Temperature, VIN = 0 V 100k 1M Effective Aperture Delay vs.
AD781 Signal-To-Noise and Distortion (S/N+D) Ratio—S/N+D is the ratio of the rms value of the measured input signal to the rms sum of all other spectral components below the Nyquist frequency, including harmonics but excluding dc. The value for S/N+D is expressed in decibels. DEFINITIONS OF SPECIFICATIONS Acquisition Time—The length of time that the SHA must remain in the sample mode in order to acquire a full-scale input step to a given level of accuracy.
AD781 DYNAMIC PERFORMANCE (VOUT HOLD – VIN ), mV VOUT ACQUISITION ACCURACY – % The AD781 is compatible with 12-bit A-to-D converters in terms of both accuracy and speed. The fast acquisition time, fast hold settling time and good output drive capability allow the AD781 to be used with high speed, high resolution A-to-D converters like the AD674 and AD7672. The AD781’s fast acquisition time provides high throughput rates for multichannel data acquisition systems.
AD781 Measurements of Figures 7 and 8 were made using a 14-bit A/D converter with VIN = 10 V p-p and a sample frequency of 100 kSPS. common pin should also be connected to the digital ground, which is usually tied to analog common at the A-to-D converter. Figure 4 illustrates the recommended decoupling and grounding practice. 1% NOISE CHARACTERISTICS 1/2 BIT @ 8 BITS Designers of data conversion circuits must also consider the effect of noise sources on the accuracy of the data acquisition system.
AD781 AD781 TO AD674 INTERFACE 20 Figure 9 shows a typical data acquisition circuit using the AD781, a high linearity, low aperture jitter SHA and the AD674 a 12-bit high speed ADC. The time between the AD674 status line going high and the actual start of conversion allows the AD781 to settle to 0.01%. As a result, the AD674 status line can be used to control the AD781; only an inverter is needed to interface the two devices.
