72BD Boonton Capacitance Meter
- Measurement range: 2 pF to 2000 pF full scale
- Test Frequency: 1 MHz
- Test level: 15 mV
- ±600 V external bias capability
- DC output response time to 50 μs
All Boonton capacitance meters make rapid, accurate, low test-level, three-terminal measurements of shunt capacitance. Measurements are unaffected by the shunt loss of the test component down to Q values as low as 1.
If the loss of the test component is predominantly in series, as is the case with most junction capacitance measurements, the capacitance indicated is also essentially the same as the equivalent series capacitance value, provided that the series loss does not result in a Q value below 10.
The Boonton 72BD is recommended for most measurements where a 1 MHz test frequency is specified, but especially where the fastest DC output response is required.
Three-terminal input configuration is needed to accurately measure low values of capacitance in the presence of relatively large values of shunt capacitance to ground. The Model 72 Series provides two types of three-terminal input connection adapters as standard.
All Model 72 Series instruments use a phase-sensitive detector that effectively ignores the quadrature signal associated with capacitor loss. As a result, accurate shunt capacitance measurements may be made on components whose Q is as low as 1.
Provision for DC Bias
DC bias up to ± 600 V may be applied to the test specimen through fused rear panel terminals from an external floating supply. This voltage appears between HI and LO posts on both the TEST and DIFF inputs, making it possible, for example, to compare the C-V characteristics of two varactors.
Two separate bias voltages may be applied between HI and ground and LO and ground. This is convenient when making small-signal capacitance measurements on transistors because it allows separate bias on both test terminals, or either HI or LO post to be at DC ground.
The 72BD has remote control capabilities of capacitance ranging via TTL logic inputs. In addition, the digital Model 72BD allows control of auto range, hold and trigger and has serial BCD outputs as standard, and parallel BCD outputs as an option. Autoranging capability is standard on the 72BD. A Model 10A-03 Bus Interface Unit is available to adapt the Model 72BD to the IEEE-488 data bus. A separate 8" x 10" x 3" cabinet is cabled directly to a rear panel connector and allows the 72BD to be addressed as either a listener or a talker. All functions, except zeroing, can then be under the direction of a remote controller.