update 2008-05: This page describes a deprecated project design. Please see for the successor project.
This page describes the design decisions and specifications of a portable (handheld, battery-powered) digital oscilloscope based on a LABRADOR3 ASIC developed at the University of Hawaii / department of physics / instrumentation development lab. Development was started on the oscilloscope in January, 2008.
In the above block diagram, the top portion (in blue) is the main circuit board and the bottom portion (in green) is the oscilloscope daughterboard. Red lines indicate analog signals and black lines are digital signals.
The LABRADOR3 is a 9-channel high-speed 12-bit analog-to-digital converter with a narrow buffer (260 samples per channel). It has two modes of operation. First, it acts as a high-speed 9-channel switched-capacitor buffer. This array of capacitors stores charge for later analog-to-digital conversion and gets overwritten in a circular fashion until the desired data is in the buffer, at which time it stops collecting data. The next mode is the Wilkinson analog-to-digital conversion stage. This occurs simultaneously for all 2340 samples. After the data is converted into digital values, the data can be read out by a microcontroller or FPGA in a random fashion via an address and data bus.
The LABRADOR3 is capable of sampling up to 3.7 x 10^9 times per second, leading to a timing measurement precision of approximately 0.27ns. The analog bandwidth, however, is limited to about 900MHz. One of the goals of the design of this oscilloscope is that it not attempt to limit this timing precision or analog bandwidth in any way.
A 2.5V power supply is required by the LABRADOR3.
main circuit board
The main circuit board contains the ARM9 microcontroller, SDRAM and SPI flash memory for holding the program. It also contains a pair of SD/SDHC card slots so that data can be stored indefinitely. It also has a few extraneous circuit elements because it is a dual-purpose circuit board and the other use had functionality that will go unused in this application.
oscilloscope circuit board
The LABRADOR3 is a single-supply AtoD converter (and, moreover, it can only measure signals between 0.5V and 2.0V), so in order to measure a greater dynamic range and allow the input voltages to swing negative, an operational amplifier is used in a summing configuration (to add an offset) with an array of selectable resistors (to set the gain for the input signal).