Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1999-09-20
2001-05-22
Grimm, Siegfried H. (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S11300A, C331S143000, C331S144000
Reexamination Certificate
active
06236280
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a voltage controlled oscillator, and, more particularly, to a low-noise, voltage controlled oscillator.
2. Description of the Related Art
In the field of wireless telecommunications, noise problems are a significant problem. For example, in cordless telephone sets, a handset and base communicate over a radio link instead of through a wire. Noise may reduce the useable range, or more problematic, even eliminate proper operation by interfering with the radio link between the handset and the base of the telephone set.
Some noise is environmental in nature. That is, some noise comes from the environment in which the telephone set is located. For example, other electronic equipment operating near the telephone set can produce EMI (electromagnetic interference) that causes noise to be impressed onto the circuitry of the telephone set. Shielding the telephone set can reduce some environmental noise, however, in applications such as cordless telephones, shielding may not be entirely effective. In fact, cordless telephones have been recently designed to operate in a frequency range (~900 MHz) that should normally be outside the range of noise produced by many home appliances. That is, the radio signals delivered between the handset and the telephone base are carried by a 900 MHz electromagnetic signal. Most home appliances do not produce EMI in this frequency range.
Another type of noise that can impair voice signal clarity arises from inside the telephone set. That is, the telephone set may produce noise internally that is impressed on the radio signal. Two examples are device noise and switching noise. Oscillators are commonly used to produce the ~900 MHz carrier signal used in cordless telephones. Any noise introduced by the oscillator will ultimately be delivered over the radio link, interfering with the proper operation.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a voltage controlled oscillator having first and second complementary output terminals is provided. A first edge delay circuit has an input terminal, an output terminal, and a control input terminal. The input terminal is coupled to the first complementary output terminal. The first edge delay circuit is capable of delivering a signal on the output terminal that varies between first and second logic levels at first and second preselected rates in response to detecting a variation between first and second logic levels at the input terminal. The first edge delay circuit is capable of varying at least one of the first and second preselected rates in response to receiving a signal at the control input terminal. A first comparator has a first input terminal, an output terminal, and a control input terminal. The first comparator first input terminal is coupled to the output terminal of the first edge delay circuit. The first comparator output terminal is coupled to the second complementary output terminal. The first comparator circuit is capable of delivering a signal on the output terminal that varies between first and second logic levels at first and second preselected rates in response to detecting a variation between first and second logic levels at said first input terminal. The first comparator is capable of varying at least one of the first and second preselected rates in response to receiving a signal at the control input terminal. The control input terminals of the first edge delay circuit and the first comparator are coupled together. A feedback circuit is coupled between the second complementary output terminals and the first comparator circuit.
In another aspect of the present invention, a voltage controlled oscillator that has first and second complementary output terminals is provided. A first edge delay circuit has an input terminal, an output terminal, and a control input terminal. The input terminal is coupled to the first complementary output terminal. A first comparator has a first, second and third input terminal, an output terminal, and a control input terminal. The first input terminal is coupled to the output terminal of the first edge delay circuit. The second input terminal is coupled to the first complementary output terminal. The first comparator output terminal is coupled to the second complementary output terminal. A second edge delay circuit has an input terminal, an output terminal, and a control input terminal. The input terminal is coupled to the second complementary output terminal. A second comparator has a first, second and third input terminal, an output terminal, and a control input terminal. The first input terminal is coupled to the output terminal of the second edge delay circuit. The second input terminal is coupled to the second complementary output terminal. The first comparator output terminal is coupled to the first complementary output terminal. The control inputs of the first and second comparators and the first and second edge delay circuits are coupled together and adapted to allow each circuit to transition from at least one logic level to another logic level at a rate responsive to the magnitude of a signal applied thereto. A feedback circuit is coupled between the first and second complementary output terminals and the third inputs of the first and second comparator circuit.
REFERENCES:
patent: 4236121 (1980-11-01), Senturia
patent: 4972162 (1990-11-01), Banu
patent: 5233315 (1993-08-01), Verhoeven
Advanced Micro Devices , Inc.
Grimm Siegfried H.
Williams Morgan & Amerson
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