Keithley KPCMCIA-12AIAOH, User Manual, Page: 18 / 58

3-2 Theory of Operation KPCMCIA-12AIAOH User’s Manual
Introduction
The KPCMCIA-12AIAOH PC card consists of four differential or eight single-ended analog
input channels, each having a bipolar input range of ±0.01V (gain = 1000), ±0.1V (gain = 100),
±1V (gain = 10), or ±10V (gain = 1) with programmable gains of 1, 10, 100, and 1000). The A/
D converter, either 12-bit or 16-bit, can be operated at its top speed of 100,000 samples per second
(10µs per sample).
The A/D converter uses left-justified 2’s complement coding. For the 16-bit version, its output
ranges from -32768 to 32767 as usual. However, the 12-bit version has its 12-bit result occupying
the most significant 12 bits and pads its least significant four bits with zeroes to make a 16-bit
output word for each converted input sample.
The KPCMCIA-12AIAOH PC card can be operated as an I/O device, occupying 16 consecutive
bytes in the I/O address space. It can also be configured to operate via memory mapped I/O. It
fully complies with the PCMCIA standard 2.1 as a type II card. The card does not have any jump-
ers or DIP switches; all of its configurable features are programmable.
Functionally, the KPCMCIA-12AIAOH PC card consists of the following components:
• DC/DC power supply
• Analog input multiplexer
• Programmable gain control
• A/D converter
• Data FIFO
• Scan list
• Trigger control
• Pacer clock
• Interrupt and status
• Digital I/O
• D/A circuit
• 16-bit timer/counter circuit
• Associated control circuits
DC/DC power supply
The KPCMCIA-12AIAOH PC card uses a standard 5V power supply for its digital circuit. The
±15V power supplies are used for the analog front end, and the 5V power supply is used
for the A/D converter. All are generated by a DC/DC converter off of the +5 digital input power
supply from the PCMCIA connector. The DC/DC converter takes 140mA, two-thirds of the
210mA total load current, from the input power supply.
According to the new PCMCIA specification, any card that takes more than 100mA must not be
blindly turned on when the card is inserted; the card must be intentionally accessed.The
KPCMCIA-12AIAOH PC card will support the new specification by providing a unique power-
down mode control. When the card is first plugged in, powered up, or reset, the DC/DC converter
shuts off so only the digital portion is up and running, taking only 70mA from the input +5 power
supply. Full-powered mode can then be activated by software.