VTO-8000

Frequency agile systems, such as digitally controlled receivers and active jamming transmitters often use externally linearized varactor-tuned oscillators. HP oscillators are monotonic making external linearization easy using analog (opamp) or digital (EPROM) linearizing techniques. The HP VTO Series has been designed with a tuning input bypass capacitance which is sufficient to provide the necessary RF filtering action yet as low as possible to maximize DV/DT characteristics for excellent tuning speeds. Used in a phase locked loop PLL circuit, a VTO provides a receiver LO with stability equivalent to the reference oscillator (usually crystal controlled), yet variable in discrete steps or continuously depending on the PLL configuration.

Another important aspect of VTOs used in an LO application is their power vs. frequency flatness (± 1.5Ê dB). This assures that once a receiver mixer is biased for best dynamic range the local oscillator drive will remain constant throughout the tuning range without complex leveling circuitry.

HP VTO-8000 Series oscillators use a silicon transistor chip as a negative resistance oscillator. The oscillation frequency is determined by a silicon abrupt varactor diode acting as a voltage-variable capacitor in a thin-film micro striplineresonator. This provides extremely fast tuning speed, limited primarily by the internal impedance of the user-supplied voltage driver. Fast settling is another feature of the HPVTO-8000 Series oscillators. Typical settling times for the VTO-8090 are <200Ê kHz within one microsecond while the VTO-8950 settles to <2Ê MHz within two microseconds referenced to ten milliseconds. The VTO-8850 combines a bipolar transistor oscillator with a GaAs FET buffer stage. This GaAs FET buffer isolates the oscillator from variations in load impedance for low frequency pulling, allows the oscillator to run lighty-loaded for low phase noise content and provides +10 dBm of minimum output power over the full tuning range. The VTO-8000 Series varactor-tuned oscillators are packaged in TO-8 transistor cans for simple installation in a conventional 50-ohm microstripline PC board. They are ideal for most compact, lightweight commercial and military equipment designs. Test fixturing is also available for lab bench test applications. See the "Test Fixtures for TO-8 Packages" section for additional information and outlines.