Hardware Reference
In-Depth Information
Fig. 7.8 SRCO proposed
by Bhaskar and Senani [ 18 ]
R 1
x
R 3
CCII−
1
z
V 0
y
C 2
R 2
C 1
2 p which can be made quite large (in fact this
value is almost the largest stability factor attainable by any SRCO).
Another noticeable feature of this circuit is that because of control of FO through
a grounded resistor R 3 the FO can be easily made voltage- controllable by replacing
the frequency controlling resistor R 3 by an FET used as a voltage controlled
resistance.
Using CCII
unity can be approximated as S F
made from LF356 type op-amp in supply current sensing mode
implemented through current mirrors made from CA3096E mixed transistor arrays
and the voltage buffer made from LM310N, the various claims of the circuit have
been verified and the capability to realize voltage-controlled-oscillator have been
verified by using the simplified single buffer based linearized VCR of [ 62 ].
It is also worth mentioning that this configuration is also implementable by the
IC CC, PA630A which however requires additional current mirrors to enable the
realization of a CCII
. In this case it is interesting to note that the VCO version can
be implemented rather easily without requiring any additional voltage followers
because of the availability of two-on chip buffers in the PA630A CC chip.
7.4 SRCOs Employing All Grounded Passive Elements
Oscillator circuits employing all grounded passive components are interesting
because of three basic reasons. Firstly, having all resistors and capacitors grounded
is attractive from the point of view of integrated circuit implementation of an
oscillator having all elements grounded. Secondly, all resistors being grounded is
useful from the point of view of electronic control of the oscillation frequency since
the frequency controlling grounded resistor(s) can be easily replaced by FET/
MOSFET-based linear voltage-controlled-resistances (VCR) [ 61 ] thereby making
the oscillation frequency voltage-controllable thereby converting the oscillator into a
VCO. Thirdly, if the resistor controlling the condition of oscillation is also grounded,
this is useful in incorporating of an automatic feedback system for stabilizing/varying
 
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