Oscillators – Ring oscillators
Reexamination Certificate
2000-05-08
2001-10-30
Grimm, Siegfried H. (Department: 2817)
Oscillators
Ring oscillators
C331S10800D, C331S17700V, C331S179000
Reexamination Certificate
active
06310523
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a wide-range voltage-controlled oscillator, and in particular to a wide-range and low-power consumption voltage-controlled oscillator applied in digital circuits and communication systems with high efficiency and low power consumption.
2. Description of the Related Art
Regardless of whether used in digital circuits or communication systems, a voltage-controlled oscillator plays a key role. In a digital circuit, the voltage-controlled oscillator is used to provide a required clock signal; and in a communication system, the voltage-controlled oscillator can provide an oscillation frequency for serving as a carrier wave or for use of a local oscillator when modulating. Meanwhile, the voltage-controlled oscillator is also a key device for both phase-locked circuits and frequency synthesizers.
In general, an oscillator is formed by an LC charge/discharge circuit. An oscillation frequency is generated by the LC charge/discharge circuit for use of above-stated circuits. Recently, since the integrity of ICs has made great progress, inductors used for ICs are no longer suitable for use in ICs manufacture.
For a better stability of an output frequency from an oscillator of a chip, a ring oscillator is usually adopted because it is hard to control the properties of inductors and the inductors use extra area.
FIG. 1
shows a conventional wide-range phase-locked loop. Reference symbol f
ref
represents a reference frequency, f
out
represents an output frequency, S
o
and S
1
represent selecting signals, V
c
represents a control voltage. The reference frequency f
ref
is transmitted from an external circuit (not shown) to a phase detector
100
. The reference frequency f
ref
is converted into the control voltage V
c
after passing through a charge pump
102
and a loop filter
104
. The control voltage Vc and the selecting signals S
0
and S
1
together are inputted to a wide-range voltage-controlled oscillator
106
. At this time, the wide-range voltage controlled oscillator
106
outputs the output frequency f
out
to a required circuit (not shown). Furthermore, a divider
108
receives the output frequency f
out
coming from the wide-range voltage-controlled oscillator
106
and then outputs a corresponding frequency by dividing the output frequency f
out
with a certain multiple. Using the phase detector
100
, the corresponding frequency is compared to the reference frequency f
ref
thereby to determine whether the output frequency f
out
is a required frequency.
FIG. 2
shows a ring voltage-controlled oscillator
200
, having an odd number of inverters
202
electrically connected in series. That is, the output terminal of each inverter
202
is electrically connected to the input terminal of its next inverter
220
, and the like, and the output terminal of a last inverter
202
is electrically connected to the input terminal of a first inverter, thereby forming a closed loop. With a time delay caused by each inverter
202
, an oscillation frequency can be generated. The period of the oscillation frequency is dependent on the entire time delay of the inverters
202
.
Moreover, there is a voltage control load electrically connected between the output terminal of each inverter
202
and ground. The voltage control load consists of a voltage control resistor VCR
204
and a capacitor C
206
electrically connected in series. By adjusting the control voltage V
c
on the voltage control resistor VCR
204
, the charge/discharge time between two adjacent inverters
202
can be changed thereby to control the oscillation frequency. The time delay can be approximately equal to a RC time constant, wherein the C is the capacitance of the capacitor C
206
and R is an equivalent resistance of the voltage control resistor VCR
204
. The equivalent resistance is dependent on the sizes of transistors inside the inverters
202
.
The period of the output oscillation frequency is positively proportional to the RC time constant. In other words, the oscillation frequency is inversely proportional to the RC time constant. Therefore, the power consumption of the ring voltage-controlled oscillator
200
can be expressed by:
P=C*V
2
*f
Wherein, C is the capacitance of the capacitor C
206
, V is a power supply voltage and f is an oscillation frequency. If the oscillation frequency f is replaced with the RC time constant, the power consumption can be obtained by:
P=K
p
*(
C*V
2
)*(1
/RC
)=
K
p
*V
2
/R
Wherein, K
p
is a constant, representing the number of the inverters
202
. It can be known from the above-stated equation that the power consumption of the ring voltage-controlled oscillator
200
is a constant once the sizes of transistors is decided, and is independent of the oscillation frequency.
Generally, to increase the range of the output frequency of the oscillator, the ring oscillator must generate and transmit a high-frequency clock signal to a frequency synthesizer, and in response to the high-frequency clock, the frequency synthesizer can generate a clock having various frequencies. Furthermore, the wide range of output frequency can also be obtained by increasing the number of the inverters. However, Increasing the number of the inverters results in more power consumption.
As to the stability of the output frequency, the oscillation frequency of the ring oscillator is adjusted during time change in a transient region. Therefore, the ring oscillator will be easily affected by noises and temperatures, resulting in a poor stability on the output signal.
SUMMARY OF THE INVENTION
In view of the above, the invention provides a wide-range and low power consumption voltage-controlled oscillator which includes a plurality of series controllable inverter banks electrically connected in parallel, voltage control resistors, capacitors and a control unit. Under the same output load, the control unit is used to select the number of the series controllable inverter banks electrically connected in parallel for adjusting the driving ability thereof.
A wide-range and low power consumption voltage-controlled oscillator according to the invention includes a logic control circuit, a parallel series controllable inverter bank and a voltage control load. The logic control circuit consists of a plurality of logic gates for receiving a selecting signal from an external device and then transmitting a control signal. The parallel series controllable inverter bank consists of a plurality of series controllable inverter banks electrically connected in parallel for receiving the control signal and outputting an oscillation signal, wherein the control signal is used to control the number of the series controllable inverter banks electrically connected in parallel. The voltage control load is electrically connected between the parallel series controllable inverter bank and ground for serving as a load of the parallel series controllable inverter bank.
Each series controllable inverter bank consists of output terminal switch controllable inverters. Each output terminal switch controllable inverter includes a PMOS transistor, an NMOS transistor, an inverted logic switch and a non-inverted logic switch, wherein the drain of the PMOS transistor is electrically connected to a power supply while the drain of the NMOS transistor is electrically connected to ground, and the inverted logic switch and the non-inverted logic switch are electrically connected between the PMOS transistor and the NMOS transistor.
Furthermore, each series controllable inverter bank consists of power supply switch controllable inverters. Each power supply switch controllable inverter includes a PMOS transistor, an NMOS transistor, an inverted logic switch and a non-inverted logic switch, wherein one terminal of the inverted logic switch is electrically connected to a power supply while one terminal of the non-inverted logic switch is electrically connected to ground, and the PMOS transistor and the NMOS transistor are electrically connected between the inverted lo
Chen Oscal Tzyh-Chiang
Sheen Robin Ruey-Bin
Grimm Siegfried H.
Huang Jiawei
J. C. Patents
National Science Council
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