recommended ADC driver, external reference and reference buffer options?

Question What are the recommended ADC driver, external reference and reference buffer options? Answer The AD7961 datasheet recommended ADC drivers are the two single-ended op amps ADA4899-1 and AD4897-1 or differential amplifier ADA4932-1. The low-noise, low-power AD8031 rail-to-rail amplifier is recommended to buffer the external reference and the common-mode (Vcm) output voltage of the AD7961. The recommended low noise, low-drift external precision voltage references for the AD7961 are the ADR4520/ADR4540/ADR4550 and ADR440/ADR444/ADR445.

What are the reference options available for the AD7961?

Question What are the reference options available for the AD7961? Answer The AD7961 conversions are referred to a 5 V or 4.096 V reference voltage. There are three options for using an external reference. • Externally buffered reference source of 5 V applied to the REF pin. • Externally buffered reference source of 4.096 V applied to the REF pin. • External reference of 2.048 V applied to the REFIN pin (high impedance input). The on-chip buffer gains this by 2 and drives the REF pin with 4.096 V. The various options for using the above any of the above references are controlled by the EN1 and EN0 pins. Refer to the datasheet Table 8 for further information.

Question Page 17 of data sheet rev c set the enables to 0100X, to get test pattern out of the adc serial link. Great, can include that in the self test code fo the unit to prove the adc interface is working and meeting timing, BUT what is the pattern ? I can’t make a checker of the pattern unless I know the pattern , I guess PRBS or walking ones or alternate 1, 0 , 1 but, can’t find it specified anywhere, Answer The AD7960 generates an 18-bit pseudo random test pattern based on the polynomial series - . To generate this pattern, you need to power-up the AD7960 and set EN[3:0] = 0100. Then Initiate a conversion CNV± and run the CLK± at 200MHz (max up to 300MHz). The pseudo random generator is reset into a known state at the start of the first conversion. At the end of conversion, the pseudo random number is loaded into the LVDS block instead of the 18-bit conversion result. The pseudo random number can be read back the same way the conversion result is read back. To exit this mode, you need to change EN[3:0] from 0100 to any other combination mentioned in the datasheet.

Question What is AD7961? Answer The AD7961 16-bit, 5-MSPS PulSAR differential ADC, uses a capacitive digital-to-analog converter (CAPDAC) based successive-approximation register (SAR) architecture to provide the unprecedented speed, noise and linearity performance without latency or pipeline delay. The AD7961 is offered in a 5mm X 5mm, 32 lead, Lead Frame Chip Scale Package (LFCSP_WQ) and it is specified over the –40°C to +85°C industrial temperature range. The AD7961 consumes 39 mW (typ) at 5 MSPS and is optimized for excellent AC and DC performance even at full 5MSPS throughput. • Dynamic range: 96 dB • SNR: 95.5 dB • THD: −116 dB • INL: ±0.2 LSB (typical), ±0.55 LSB (maximum) • DNL: ±0.14 LSB (typical), ±0.25 LSB (maximum) The AD7960 is an 18-bit, 5 MSPS PulSAR differential ADC and is pin compatible with the AD7961 PulSAR family, so it can be used instead of the AD7961 when only 18-bit performance is required.

What power supplies does the AD7961 require? Does it power down?

Question What power supplies does the AD7961 require? Does it power down? Answer The AD7961 operates from 1.8V and 5V supplies (VDD1 = +5V, VDD2 = +1.8V, VIO = +1.8V), dissipating only 39 mW at 5-MSPS when converting in self-clocked mode. The power dissipation scales linearly with throughput. When powering up the AD7961 device, first apply 1.8 V (VDD2, VIO) to the device, then ramp 5 V (VDD1) and apply an external reference voltage. Apply the analog inputs last. The AD7961 powers down when EN3 to EN0 = X000 and operates in snooze mode when EN3 to EN0 = XX11 using the correct reference choice. Refer to CN-277 or UG-581 for complete information on how to generate the required supplies for the AD7961.

AD7960 LVDS test pattern

Question Could you forward me LVDS test patterns for AD7960 ADC, I cannot find them in the data sheet. Answer The AD7960 generates an 18-bit pseudo random test pattern based on the polynomial series - . To generate this pattern, you need to power-up the AD7960 and set EN[3:0] = 0100. Then Initiate a conversion CNV± and run the CLK± at 200MHz (max up to 300MHz). The pseudo random generator is reset into a known state at the start of the first conversion. At the end of conversion, the pseudo random number is loaded into the LVDS block instead of the 18-bit conversion result. The pseudo random number can be read back the same way the conversion result is read back. To exit this mode, you need to change EN[3:0] from 0100 to any other combination mentioned in the datasheet.

Evaluation board for the AD7961

Question Is there an evaluation board for the AD7961? Answer Yes, the EVAL-AD7961MCZ board can be used to evaluate the AD7961 part, which is compatible with the System Demonstration Platform (SDP) board - EVAL-SDP-CH1Z. Refer to UG-581 for complete information on the EVAL- EVAL-AD7961MCZ test setup. •http://www.analog.com/EVAL-AD7961

Can the ADC inputs exceed the reference voltage or go below ground?

Question Can the ADC inputs exceed the reference voltage or go below ground? Answer The ADC inputs should not exceed the reference voltage or go below ground by more than 0.3V as this may result in the ADC being damaged. If this is a common condition then Schottky diodes should be used to protect the inputs and limit them to Transient currents of up to 100 mA do not cause SCR latch-up on the REF pin.

AD7960: Target markets/applications for this product

Q What are the target markets/applications for this product? A The AD7961 offers unprecedented speed, noise, and high accuracy and it is designed for low-power signal chains, multiplexed systems such as digital X-ray, and oversampling applications including spectroscopy, MRI gradient control and gas chromatography. It significantly reduces power dissipation and cost in multichannel applications such as: • Digital imaging systems • Digital X-rays • Computed tomography • IR cameras • MRI gradient control • High speed data acquisition • Spectroscopy • Test equipment

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