Abstract : AD9244 is manufactured ANALOG DEVICES high-speed high-precision 14-bit AD converter. It has a 750MHz input bandwidth, the maximum allowable sampling rate up to 65MHz. It is specifically applied to less than 2V peak to peak small-signal analog-digital conversion system, its greatest feature is the small size , low power consumption and high accuracy. This paper introduces the main features of AD9244 and pin function , given the typical application circuit AD9244 . Keywords : AD converter ; data sampling rate ; AD9244 1 Overview AD9244 is AD the company launched a 14-bit high-precision high-speed ADC . It consists of an analog voltage +5 V power supply, can also +3 V or +5 V digital voltage work. AD9244 provide on-chip reference voltage , and integrated high-performance sample and hold amplifier . Under normal operating conditions , the highest sampling rate of up to 65MSPS. AD9244 differential sub- circuits using multiple internal structure and logic circuits with automatic error correction , you can input data rate of 65MSPS guarantee the accuracy of 14bit . In addition, the device also has a wide operating temperature range , can be -40 ° C to +85 ° C temperature range work. AD9244 has 750MSPS analog input signal bandwidth . 65MSPS 5V supply voltage and the input data rate, the device 's power consumption is only 590mW, and the differential nonlinearity error of only ± 0.6LSB, while at the Nyquist sampling rate can get 74dB of SNR and 83dB of SFDR. AD9244 can be designed to handle peak value of 1 ~ 2V analog small signal . Its input signal and clock signals can be differential input form to enable the system to get the best performance. 14-bit digital output signal can be expressed directly in binary form , can also be a complement binary form . An overflow that bit (OTR) can be used to output overflow signal , this signal and a 14-bit signal in a certain way with the highest combined to determine the input signal is on the overrun or under the overflow . AD9244 uses advanced CMOS manufacturing process , a 48 -pin surface mount package . Therefore, it can be used for small-signal communications subsystem , high-end image processing equipment and high-frequency devices. AD9244 features are as follows : ? single +5 V analog power supply, digital power supply +5 V or +3 V are two options ; ? high precision , small- signal input for 1V , AD9244 with 14bit precision ; ? high speed , the maximum sampling rate of up to 65MSPS; ? Low power consumption , in 40MSPS sampling rate, power consumption is only 340mW, at 65MSPS sampling rate, the power consumption of 590mW; ? Input frequency bandwidth, with bandwidth of 750MHz analog input signal ; at the highest sampling rate up to 74dB signal to noise ratio ; ? On-chip integrated high-performance sample and hold amplifier , the input signal can be used single-ended input and differential input can also be used ; ? chip offers +1 V ~ +2 V reference voltage , and can interface resistance by changing set ; ? with overflow that bit (OTR), when the input signal outside the normal scope of work set to 1 ; ? high-speed parallel output interface ; ? highly under-sampled , and when the input signal to 100MHz, when the sampling frequency of 65MSPS , SNR up to 70dB, SFDR up to 82dB; ? 48-pin surface mount package . 2 pin function Figure 1 is a functional block diagram of AD9244 . One SHA for the high-performance amplification and hold amplifier ; then use 8 channel ADC and DAC structure to achieve the conversion of the input signal and error correction ; timing module for processing the input clock ; reference module is used to provide reference Voltage ; output register output is usually connected to the 14-bit digital output pins . Figure 2 AD9244 pinout diagram . The basic function of each pin is as follows : VIN +, VIN-: analog signal input. Single input form, the VIN + input signal termination , VIN- grounded ; differential form of input analog signal , VIN +, VIN- differential signals were received at both ends . Differential input in the form of high-precision high-speed applications for easier access to good results. In general, the input signal is single form , so often dedicated 1:1 transformer or a differential conversion chip to achieve the single signal to differential signal conversion. CLK +, CLK-: the clock signal input . And VIN +, VIN- similar input clock can also be two single- input and differential input form , but in the AD9244 's internal end- all to a single differential input clock signal into the form . The quality of the input clock signal ADC results have great impact , it should try to ensure the purity and accuracy of the clock signal and the clock input signal to avoid interference . DUTY: clock stable signal . The high termination when the external input in internal clock to adjust the duty cycle to produce an accurate 50% duty cycle clock signal . REFSENSE, VREF, REFGND: internal reference voltage pin . These three pins can have different connections within 1V ~ 2V reference voltage , in the three -pin connection between the appropriate resistance can also generate random between 1V and 2V reference to any voltage . REFT, REFB: ADC internal reference voltage decoupling pin . The two pins of the AD9244 output voltage is within the actual reference voltage . Between them should 10µF electrolytic capacitor decoupling , taking a 0.1µF small capacitor in parallel , so that effect may be better. Each pin must be grounded with a 0.1µF capacitor . CML, VR: AD9244 internal use of the analog bias point , usually the client will have more than 300µA of current , it must be grounded with a 0.1µF capacitor for decoupling . OEB: output allows pin . AD9244 has three-state output. If the OEB ground , then the AD9244 's output driver will be activated , and outputs the converted digital signal ; OEB then if high , the output signal output pin is high impedance state . DB0 ~ DB13: data output pin , where the highest bit DB0 . OTR: overflow direction voltage pin . When the OTR output to 1, that can convert the input voltage exceeds the voltage range of AD . OTR and DB0 simple logical combination can accurately determine the input voltage is under the overflow or overflow . DFS: output data format selection pin . When the DFS access number to the output data for the direct binary form; when DFS access digital power , the output data for the binary complement form . Figure 3 AD9244 typical external circuit Click to enlarge 3 Typical Application Circuit Figure 3 is a typical AD9244 external application circuit . One analog power , analog ground and digital power and digital ground are respectively from the external input . Analog input and clock signals are differential input form input in order to get the best ADC effect . REFSENSE, VREF , and REFGND through a 10µF capacitor and a 0.1µF capacitor connected to a small , providing an internal reference voltage of 1V . Analog input signal peak value is embedded within the 1V , but the clock frequency can reach 65MHz. REFT and REFB should be grounded through a capacitor network , and CML , and VR also should be grounded through the 0.1µF capacitor . DUTY received analog signal power can AD9244 input clock duty cycle adjustment of 50% . OEB pin to ground will enable the output enable ; DFS through the 1kO resistance grounding , choose the output data for the direct binary form . The output data pin through 22O resistor connected to the next level of digital circuits, can prevent the output current is too large, while there are other digital circuit isolation and reduce interference. Analog power and analog , the digital power and digital ground should be made through the decoupling capacitor network , to reduce the input noise power . In practical applications, the analog ground and digital ground preferably in the form of strata , and the analog ground and digital ground should be a single point under the ground in the chip . In addition, because AD9244 is a static sensitive device , the board should also adopt various anti-static measures to ensure the normal operation of AD9244