• Low volume (<250 pcs/day) testing of mixed signal ICs for both, wafer and module test.
• Characterization of mixed signal ICs
• IC / Module debugging
• Testing / Debugging of RF ICs and modules which require high LF stimulus count (i.e. RF section is covered by GPIB instruments while LF stimulus is done by test hardware presented here)

The realized test system is described in the following using a particular project as an example. The DUT in this project has the following key data:

Setting up the test environment

Each ASIC has its own special requirements. This holds true even more for analog/mixed-signal ASICs which may have a lot of unstandardized I/O. In order to be prepared for future requirements in testing we build a test system which incorporates already in-house available RF test equipment. This equipment is enhanced by a ADwin-pro real-time measurement system for LF stimulus and measurements. ADwin-pro is a modular system having its own controller (DSP) with memory, and can be extended with several types of measurement cards. Currently our system contains 24 DAC channels (16bit), 64 ADC channels (14bit) and 32bit digital I/O. A Microsoft Windows based Host-PC is running a Visual Basic program which controls the overall test flow. The Host-PC communicates with ADwin via Ethernet and with several other instruments via GPIB. A wafer prober is also driven by GPIB, allowing us to run extensive automatic wafer tests. If required, measurement capabilities can be extended by either adding cards to the ADwin system or by including further GPIB instruments. The photograph below shows the test system currently used. Additionally, the system overview including the signal flow is shown on the left.

Pin Electronic

Usually a prober uses a pin electronic to transmit and receive arbitrary signals through various interface types. Although we have A/D and D/A cards which support the range of +/- 10 volts, these cards cannot be connected directly to the DUT, but a pin electronic is used. Reasons are:

• The DAC output current is limited to 5mA, which is far to low for driving 50 Ω loads. A buffer on our pin electronic enhances the driving capability to 100mA.
• The input resistance of the I/O's need to be measured. For this purpose, every channel has a selectable output resistancee (currently 50Ω, 1kΩ, 10kΩ). An A/D channel is used to measure the voltage drop across the resistor to calculate either driving/bias current and/or input resistance.
• Some I/O's of the DUT need a specific termination (in our case 50 Ω) for testing, which is implicitely provided by the pin electronic.
• Additionally, the "upper" DAC channel can be routed to the output to generate high slew rates by mux switching rather than DAC reprogramming

The diagram below shows a simplified block diagram of one pin electronic channel.

Currently our pin electronic is equipped with 24 identical channels as shown above. Of course it is possible to extend this further. But since there is no need in the project described here to drive all 35 inputs at the same time, we have developed a Multiplexer Board as an economic way to serve all inputs and additionally measure the resistance of the DUT outputs.

Multiplexer Board

The pin electronic is extended with a multiplexer board. This board maps the 24 pin electronic channels to various chip I/Os and also utilizes the remaining ADC channels for monitoring the DUTs outputs. As a result 24 input pins of the DUT can be driven in parallel, but the total amount of input pins used during testing can be much higher (in this specific example we serve 35 inputs). Both, the amount of parallel I/O and the number of multiplexed channels can be extended easily by adding cards to the ADwin system and/or the pin electronic. An additional multiplexer matrix is used to measure the resistance of the DUT outputs. Furthermore, to enhance debugging, one can snoop into a selected part in the test program and display the pattern on an oscilloscope by using an adaptor and a software controlled trigger output.

Software

The software consists of two programs interacting with each other. The ADwin real-time system is programmed in ADbasic (a basic dialect, which is compiled to ADwin executables). The ADbasic program contains all testing sequences etc. and drives the DAC and ADC channels as well as setting up the pin electronic. Additionally, all data measured during one cycle are stored in the ADwin system. On the other hand we have a host computer running an Visual Basic program. This program does all user interaction (see screenshot), controls the wafer prober and execures longer test sequences (e.g. test of complete wafer, multiple tests per die/module etc.) and drives the GPIB instruments. After test completion, the VB program reads measured data from ADwin, displays some key information and stores all data to disk.
Both, the ADbasic and Visual Basic programs were written modular to enable easy transfer to other measurement tasks.

Testing

In the project used here as an example every IC is tested for I/O termination, supply and voltage drop, input bias currents, output voltage swings, threshold settings with hysteresis and logic verification of all IC modes. Furthermore excessive ring oscillator tests are performed using an external frequency counter controlled via GPIB. Overall test time is approx. 17 sec with ring oscillator tests consuming 13 sec.

Benefits of MICRAM test setup

• Modular Concept: Number of channels is easily extensible.
• Real-Time System: Predictable timing of analog signals
• Visual Basic Control Program: Easy to use (Windows Software); Measured data can be exported to any windows application.
• Inclusion of GPIB: For non-realtime measurements GPIB-Instruments can be used. This extends measurement capabilities for RF-applications dramatically.
• Efficient: On-wafer and Module tests as well as characterization and debugging with identical hardware.