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Temperature-Compensated, Wide-Range, Voltage-Controlled Oscillator

IP.com Disclosure Number: IPCOM000099752D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 89K

Publishing Venue

IBM

Related People

Buchholtz, TC: AUTHOR

Abstract

A high-speed, temperature-compensated voltage-controlled oscillator (VCO) function designed for monolithic integration has balanced temperature coefficients of devices and elements to provide a temperature-compensated operating frequency range. The external voltage swing is largely determined by a ratio of resistor values, which is also stabilized by the tracking of on-chip components placed in close proximity. The design avoids the use of excessively small resistor values, preventing the need to use many resistor bars in parallel to achieve an acceptable resistor tolerance.

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Temperature-Compensated, Wide-Range, Voltage-Controlled Oscillator

       A high-speed, temperature-compensated voltage-controlled
oscillator (VCO) function designed for monolithic integration has
balanced temperature coefficients of devices and elements to provide
a temperature-compensated operating frequency range.  The external
voltage swing is largely determined by a ratio of resistor values,
which is also stabilized by the tracking of on-chip components placed
in close proximity.  The design avoids the use of excessively small
resistor values, preventing the need to use many resistor bars in
parallel to achieve an acceptable resistor tolerance.

      The figure shows a schematic of the VCO.  Partial temperature
compensation is achieved if a voltage with a zero temperature
coefficient at the emitters of Q3-Q5 is developed.  Such temperature
compensation is easily accomplished using standard design techniques.
 BG1 is a voltage reference supplied for this purpose.  The currents
through resistors R5, R6, and R8 have a temperature coefficient
inverse that of the resistors themselves.  This allows the
temperature coefficient of the current through the external capacitor
to partially offset the coefficient of the voltage across it.
Therefore, resistors are of the same type and in a balanced design,
R5=R6 and R7=R9.

      Adjustment of the output frequency is made by varying the
CONTROL input.  In normal linear operation, Q3-Q7 are always active,
and CONTROL establishes the balance of current between Q3-Q5.  As
CONTROL increases, the current in Q3-Q4 increases with an associated
increase in the operating frequency and a corresponding decrease in
the current through Q5.  As CONTROL decreases, the reverse occurs.
As long as Q5 remains active, it provides a bias current to D1 which
varies as CONTROL varies but is sufficient to keep D1 on.  In this
way, the collector of Q5 remains approximately 1 VBE below the supply
at all times.  The VCO provides a large signal oscillation developed
across an external ca...