8-Channel Simultaneous Sample/Hold I/O Module

Most PC-based data acquisition systems employ only one A/D converter to minimize size and cost. Under these circumstances, channels must be read sequentially. The result is that the data representing each channel is separated in time by the finite speed of the A/D (typically, 5 to 100µSec). Utilizing SSH techniques, you can minimize time-skew by capturing inputs simultaneously. This is useful in many applications, including power and other phase-sensitive measurements.

The PCI-20363M-2 option module provides up to 8 channels of simultaneous sample/hold (SSH) for any expandable Intelligent Instrumentation I/O board. All module functions are completely software programmable; no jumpers are required.

Board Architecture - Each single-ended analog input on the PCI-20363M-2 is connected to a separate sample/hold (S/H) circuit. Internal logic ensures that upon a hardware or software command, all channels are captured (held) at the same instant in time. The outputs of the S/Hs are then multiplexed onto the I3 bus for A/D conversion by the analog input subsystem on the host board. The offset voltage and gain accuracy are calibrated at the factory, but you can also calibrate them for optimum performance.

Multiple PCI-20363M-2 option modules can be used in combination to support 40 or more simultaneous channels. If your application requires more than 16 simultaneous channels (more than two PCI-20363M-2 modules and, thus, more than one board), you must plug additional modules into a PCI-20041C Series board, which has an interboard communications bus.

An internal channel scan list controls the high-speed multiplexer of the PCI-20363M-2. You can coordinate the scan lists of other modules, including A/D and channel expanders (multiplexers), so that an arbitrary sequence of up to 128 channels will be scanned and converted.

The trigger portion of the SSH module includes a group generator. When the module receives a single input pulse or software command, it produces a series of pulses that corresponds to the total number of channels to be read at the fastest rate supported by the analog input subsystem on the host board. The trigger for the burst generator can originate from the rate generator on the host board, from an optional counter/timer module, or from an external signal. In either case, the burst output includes pulses for, and is routed to, all analog input devices - including the analog input subsystem on the board or any attached option modules.

You can also interface the single-ended output of the SSH to a differential input A/D converter. For example, you would do this if you wanted to use simultaneous sampling in conjunction with the PCI-20341M-1 High-Resolution Analog Input module or a PCI-20098C Series Multifunction Board in its differential mode. An analog switch automatically connects the unused differential input to ground when SSH channels are being read. This information is contained in the channel scan list.

• Up to 8 Channels Per Module

• Multiple Modules Supported

• Completely Software Programmable

• 5nSec Channel-to-Channel Skew

• Supports up to 180kHz Channel Throughput Rate

• Supports DMA Operations

Parameter	Conditions	Specifications
Analog Inputs
Number of Channels	Single-ended	8
Voltage Ranges		±10V (dc + peak ac)
Overvoltage Protection	Power on	±12V
	Power off	±10V
Gain Accuracy	Gain = 1	±0.02%
Offset Voltage	RTO	±2.44mV
Bias Current		±40nA
Input Impedance		10M ohms/12pF
Linearity Error		0.012%, 0.5LSB
Skew Time	Channel-to-channel	5ns
Acquisition Time	To 0.01%	3.2us
Aperture Delay	To 0.01%	30ns
Aperture Uncertainty		5ns
Droop Rate		5uV/ms
Hold Step		10mV
System Throughput*
	8 simultaneous channels on PCI-20501C-1;	385K channels/second
	±2LSB; F= N/(N-1)T1+T2)**
Physical Characteristics
Power Requirements***	+5V	500mA
	+15V	40mA
	-15V	50mA
Operating Temperature Range		0 to 70° C
* Hardware limit only. Software may reduce speed.
** N = Number of Channels; T1 = 2.5msec or A/D convert time, whichever is greater; T2 = 3.2msec.
*** Refer to the data sheet of the host board to determine available power.