The AD7874 is a four-channel simultaneous sampling， 12-bit data acquisition system. The part contains a high speed 12-bit ADC， on-chip reference， on-chip clock and four track/hold amplifiers. This latter feature allows the four input channels to be sampled simultaneously， thus preserving the relative phase information of the four input channels， which is not possible if all four channels share a single track/hold amplifier. This makes the AD7874 ideal for applications such as phased-array sonar and ac motor controllers where the relative phase information is important. The aperture delay of the four track/hold amplifiers is small and specified with minimum and maximum limits. This allows several AD7874s to sample multiple input channels simultaneously without incurring phase errors between signals connected to several devices. A reference output/reference input facility also allows several AD7874s to be driven from the same reference source. In addition to the traditional dc accuracy specifications such as linearity， full-scale and offset errors， the AD7874 is also fully specified for dynamic performance parameters including distortion and signal-to-noise ratio. The AD7874 is fabricated in Analog Devices’ Linear Compatible CMOS （LC2 MOS） process， a mixed technology process that combines precision bipolar circuits with low-power CMOS logic. The part is available in a 28-pin， 0.6“ wide， plastic or hermetic dual-in-line package （DIP）， in a 28-terminal leadless ceramic chip carrier （LCCC） and in a 28-pin SOIC.