Oscillators – Ring oscillators
Patent
1998-03-02
1999-12-28
Grimm, Siegfried H.
Oscillators
Ring oscillators
330252, 330254, 331109, 331115, 331135, 331177R, H03B 502, H03B 506, H03L 500
Patent
active
060087013
ABSTRACT:
A quadrature oscillator based on two cross-coupled gm/C cells utilizes the inherent nonlinearity of positive and negative impedance cells to control the amplitude of oscillation, thereby simplifying the oscillator and eliminating the need for an outer control loop. The oscillator includes a pair of cross-coupled gm/C stages. A negative impedance cell is coupled to each gm/C cell for assuring proper start-up and enhancing the amplitude of oscillation. A positive impedance cell is also coupled to each gm/C cell to dampen the amplitude of oscillation. The transconductance of each impedance cell varies in response to the bias current provided to the cell. Thus, by controlling the bias currents through the cells, the negative and positive impedances seen by each gm/C cell can made to cancel at the desired oscillation amplitude, so that the circuit oscillates without any damping or enhancement. By utilizing the inherent nonlinearity of positive and negative impedance cells, the bias currents provided to the impedance cells can remain fixed for a given frequency of operation, thereby simplifying the design of the oscillator and providing precise, robust control.
REFERENCES:
patent: 5117205 (1992-05-01), Nauta
patent: 5489878 (1996-02-01), Gilbert
patent: 5635879 (1997-06-01), Sutardja et al.
patent: 5714911 (1998-02-01), Gilbert
Analog Devices,Inc.
Grimm Siegfried H.
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