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Voltage Control Oscillation (VCO) Delta-V Circuit

IP.com Disclosure Number: IPCOM000103047D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 47K

Publishing Venue

IBM

Related People

Strom, JD: AUTHOR

Abstract

Described is a circuit (illustrated in the figure) which increases the voltage control oscillation (VCO) frequency range by 30 percent over a design which uses a fixed current in NPN Q1.

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Voltage Control Oscillation (VCO) Delta-V Circuit

      Described is a circuit (illustrated in the figure) which
increases the voltage control oscillation (VCO) frequency range by 30
percent over a design which uses a fixed current in NPN Q1.

      Frequency of oscillation (F) of VCO in the figure is given by F
= ((ICP / (4 * C * DELTA-V)).  It is desirable that the statistical
variation of F for a fixed charge-pump current (ICP) be as small as
possible.  It is also desirable that F vary linearly with changes in
ICP.  DELTA-V (DV) is the differential voltage across nodes N7 and
N8.  This is also the voltage across the capacitor as well as the
output of the VCO.  If Q5, Q5a, are conducting current, DV can be
written as follows:  Vbeq7 - (Vbeq1*R7/(R5+R7).  If Q6, Q6a are
conducting current, DV is Vbeq8 - (Vbeq1*R8/(R6+R8).  In order for
the variation of DV as well as F to be small, Vbeq8,Vbeq7 and Vbeq1
must track closely as the various circuit parameters change.

      In the circuit, the NPN Q1 is biased at ((ICP-(Vbeq1/(R8 R6))
by the current source formed by resistor R3 and NPN Q3.  NPN's Q7 and
Q7a are biased at (2*ICP-(Vbeq7/R7))/2 which is equal to the current
carried by Q8, Q8a when they are conducting current via symmetry.
Since resistors R7, R8, R5 and R6 are equal, the current in NPNs Q1,
Q7, Q7a, Q8, Q8a are all equal.  Thus, the voltage at nodes N7 and N8
track closely, and the variation of the differential voltage between
nodes N8 and N7...