(SMX2044). Signametrics SMX2040

Figure 4-16. Sourcing DC current and meas uring voltage in the two wire configuration. This function can be used for semiconductor parametric tests.

T he SM2044 synthesizes resistance using an iterative method, which requires repeated reading of the DMM to m ake corrections to the synthesized value. While in synthesizing resistance, the readings return the measured value.

There are two basic circuit types into which resistance is synthesized; current source, such as the resistance function of another Multimeter, and voltage divider type load, as in a voltage divider circuit, where one of the two resistors in the network is being synthesized as in Figure 4-16. When synthesizing a resistance into a current source, it is important to consider its compliance voltage limits. For instance, a DMM’s 20k Ohms range will typically sources

100uA, and have a compliance limit of 2.5V. This means that the DMM current source does not behave as a curren t source when the voltage at its terminals is allowed to exceed 2.5V. Therefore synthesizing a resistance value greater than 25k

Ω (2.5V/100uA) will result in the SM2044 indicating an unstable reading.

For improved accuracy, perform open terminal calibration by using the DMMOpenTerminalCal() function with all terminals are open.

The following are limits that must be observed while synthesizing resistances:

Limitations synthesizing into current source:

1) The maximum load current, I

S

, is 10mA or 3.3/R

S

whichever is smaller. R

S

is the external resistor.

2) The maximum value that can be synthesized is 6.7/I

S

– 220 or V

C

/I

S

, whichever is smaller. V

C

is the current source compliance voltage.

3) Resistance settings resolution equals 0.1mV/ I

S.

is 100

Ω.

This means that with a source current of 1uA the resolution

Limitations synthesizing into a voltage divider:

1) The maximum current the SM2044 can provide to the load is 10mA or 3.3/R

S

, or (10 – V x

) / (R x

+ R s

+

220), whichever is smaller. R

S

is the external resistor.

2) The approximate value that can be synthesized is between 0.1 * R s

to about 100 * R s

41 Signametrics