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RI(ICE)-D2A
Notes on D/A Operation The RI(ICE)-D2A can be used in AC coupled mode or DC coupled mode. The RI(ICE)-D2A employs a transformer for use in AC coupled mode. Transformers behave similarly to "Band Pass" filters. With the lower frequency propagation limit approximately equal to 400 KHz and the upper frequency limit above 80 MHz. The upper limit provides no limitations to the D/A in AC coupled mode because it resides above the Nyquist limits of the D/A. On the other hand the lower limit does provide a problem. To use the D/A converter for frequencies below 400-500 KHz DC coupled mode must be used. Since AC coupled mode provides the most frequency range, the unit is shipped AC coupled. The documentation below describes how to convert the D/A from AC coupled mode to DC coupled mode. The AD9754 D/A converter utilizes differential current outputs-IOUTA and IOUTB. These currents range between 0 and 20 mA. Data input of all Logic 1’s produces a 20mA output for IOUTA and a 0 mA output for IOUTB. Data input of all Logic 0’s produces a 0 mA output for IOUTA and a 20 mA output for IOUTB. The D/A chip expects positive binary coding, hence to achieve 2’s complement input the MSB is inverted within the FPGA on the the D/A module before data is passed to the D/A chip. Therefore, the RI(ICE)-D2A module's data input should be in 2’s complement format.
AC Coupled Mode Notes For Jumpers: "B" Position = 2-3 Short
DC Coupled Mode 1. Remove transformer X2.(White, 6 pin thru-hole component in middle of board with markings of "T1-1T".) 2. Set Jumper configurations according to the table below. Modes-Differential, Gain = 1, Non-Inverting Gain = 2, Inverting Gain = 2 **Note-For mode Differential, Gain = 1: Differential, Gain = 1 refers to the mode that the Operational Amplifier is configured for use. The Op Amp is driven differentially by a single differential pair of inputs and the op amp's gain is set = 1. Because the Op Amp is driven differentially the output analog signal will have a gain = 2. For DC coupled mode all of the components (resistors, op amps, etc.) are supplied for Differential Gain = 1 mode and Non-Inverting, Gain = 2. For Inverting Gain = 2 mode the user will need to procure some resistors (op amps are provided) from Digi-Key. (The resistors are cheap-around $0.75 for 10). Resistors are manufactured by BC Components and are distributed by Digi-Key **Warning**-Incorrect Jumper Settings and/or Resistor Values WILL Damage the D/A Module. Be sure that all Jumpers are in their correct positions and resistors are the correct values before applying power. IOUTA = Out 1 (Non-Inverting Current Output) Notes For Jumpers: Table I. D/A Output DC Coupling Amplifier Circuit Configurations
*NOTE-At time of delivery, the RI(ICE)-D2A module is configured for AC coupling. But, removing the transformer X2 and configuring the above jumpers and/or resistors will enable DC coupled output mode. All resistors are thru-hole type and are socketed for ease of replacement.
The RI(ICE)-D2A is shipped configured for AC coupling. However, the
resistors for "Differential Gain of 1" are included on the board in
their correct locations.
Below are their values:
Gain Control DC Coupled Mode Notes For Jumpers: Table II. Gain Control Using Voltage Reference, Internal (Type 1), and External Reference-Type 2
*NOTE-Type 1 Internal is the mode that the RI(ICE)-D2A is configured when shipped. By configuring the module for "External Via Potentiometer" Type 2 mode, the small "screw" on the Blue potentiometer can be turned to increase or decrease the voltage reference and therefore gain of the of the RI(ICE)-D2A. The RI(ICE)-D2A is shipped configured for internal reference. However,
the resistors are included on the board for External reference if that use is
desired. Below are their values:
Jumper Settings For Power Connections Digital 3.3V Power Source
* 3.3V Digital Power Via Voltage Regulator: Default Power Setting When Delivered ** 3.3V Digital Power Via Board Header: Not An Available Source For The ICE-PIC3T or ICE-MBT3 Analog 5V Power Source
* 5V Analog Power Via Board Header: Default Power Setting When Delivered ** 5V Analog Power Via External Power Source: No Shunt Used But The User Should Apply External 5V Power To Pins 2 & 3 Of J1.
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