3 - Installation
38
Output Compensation
High bandwidth performance and stability are achieved by using a software-switchable output
compensation circuit. This compensation circuit has two bandwidth positions to optimize the response
for two different ranges of phone capacitance. The compensation function is set using either the front
panel TYPE:CAP command located in the Output menu (see chapter 5), or the
OUTput:TYPE[:CAPacitance] SCPI command as explained in chapter 8. The circuit covers the
following capacitance ranges:
♦Low Mode: 0 to 12,000 µF
♦High Mode: 5 µF to 12,000 µF
♦H2 Mode: keeps the unit in High mode at all times
The dc source is shipped from the factory with the output compensation set to Low Mode. If you do not
know the input capacitance of the phone that you are testing, leave the input capacitance set to Low
Mode initially. This is because in Low Mode, the output of the dc source will be stable when testing
cellular phones that have virtually any input capacitance (from 0 µF to 12,000 µF). Low mode however,
has a slower transient response (see appendix A).
The High Mode output compensation setting provides faster transient response performance for phones
with input capacitances greater than 5µF. (Most phones have input capacitances greater than 5 µF.) In
High mode, operation of the dc source may be momentarily unstable with phones that have input
capacitances less than 5 µF, or if the output sense leads are not connected. Note that if the dc source
senses that there is no load on the output, it will automatically switch from High compensation mode to
Low compensation mode.
H2 Mode is an additional compensation mode that guarantees that the dc source stays in High
compensation mode at all times. This mode may be the optimal setting in cases where a large capacitor is
connected across the phone input and output 1 is sinking current. (H2 mode is not available in earlier dc
source units.)
Use the output sense detect circuit to first determine that the sense and load leads are properly connected
to the device under test. Then, if you are testing phones in High Mode and want to determine if the input
capacitance of your phone is less than 5 µF, perform the following test.
NOTE: It is important that this test is done with the dc source installed in the test system where it
will be used, since system stability is also dependent on wiring and the phone
impedance.
1. Connect the phone to the dc source and place it in standby mode.
2. Check the last two digits of the voltage reading on the front panel of the dc source.
3. If the last two digits are fluctuating, it is an indication that the phone capacitance may be less than
5 µF and the dc source is momentarily unstable.
4. Place the output compensation of the dc source in Low Mode.
5. If the last two digits of the voltage reading are now stable, your phone has an input capacitance less
than 5 µF.