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Voltage-Controlled Oscillator

IP.com Disclosure Number: IPCOM000102003D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 81K

Publishing Venue

IBM

Related People

Schulz, RA: AUTHOR

Abstract

The varactor diode has been used extensively in recent years to implement mixer oscillators which can be tuned with a DC voltage. These devices can be built in BICMOS technologies, but are limited in range by the low breakdown voltages of logic/memory processes. Consequently, there is a need to find another way to voltage-tune the kind of oscillators which can be built in BICMOS technologies.

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Voltage-Controlled Oscillator

       The varactor diode has been used extensively in recent
years to implement mixer oscillators which can be tuned with a DC
voltage.  These devices can be built in BICMOS technologies, but are
limited in range by the low breakdown voltages of logic/memory
processes.  Consequently, there is a need to find another way to
voltage-tune the kind of oscillators which can be built in BICMOS
technologies.

      The small signal output resistance of an emitter-follower
circuit has been described in (*, equation 10.15):

                            (Image Omitted)

        Ro = RE @@ (re + (RB @@ RS)/(BETA +1))        (1)
where RE is the emitter load resistor, RB ¯¯ RS represents the
equivalent source resistance in the base circuit, re is the
incremental emitter resistance of the transistor model, and BETA is
the common emitter current gain of the transistor.  Under the
conditions that the source impedance is low and the load resistance
is high, the equivalent output resistance Ro reduces to approximately
re.  The emitter resistance term re is further expanded as
 Ro Z re = (kT/q)/IE                                  (2)
where k is Boltzman's constant, q is the charge of an electron, T is
absolute temperature, and IE is the DC emitter bias current.  At room
temperature kT/q is approximately 26 mV.  The key thing to note in
equation (2) is that the emitter-follower output resistance re is
well defined by physical constants and the DC emitter current. That
is, re is predictable and can be controlled by altering the DC
emitter current.

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