Automatically calibrated frequency-synthesis apparatus

Automatically calibrated frequency synthesis device

The present invention relates to a frequency synthesis device and method, in particular to an automatic correction frequency synthesis device and method.

The oscillation frequency of a Voltage-Controlled Oscillator (VCO) can be determined by parallel inductors and capacitors. The oscillation frequency of the voltage controlled oscillator can be changed by controlling the capacitance value.

Please refer to Figure 1 for the prior art frequency synthesizer.

The frequency synthesizer includes: a voltage-controlled oscillator 120, a frequency divider 200, a frequency phase detector 300, and a low-pass filter 190. The voltage controlled oscillator 120 generates an output signal, the frequency divider 200 divides the output signal into a feedback signal, and the phase detector 300 compares the frequency and phase of the input signal with the feedback signal. If the frequency of the input signal is higher than the frequency of the feedback signal, the control voltage of the voltage controlled oscillator 120 is increased; otherwise, the control voltage of the voltage controlled oscillator 120 is reduced.

Because the voltage-controlled oscillator has multiple frequency bands, the control method is roughly adjusted with digital signals, setting the working frequency band of the voltage-controlled oscillator, and fine-tuning with analog signals to lock the output signal at a predetermined frequency.

The frequency synthesis device proposed by US6,731,176 sets the voltage-controlled oscillator at the starting frequency band and uses a frequency-locking detector to detect whether the frequency has been successfully locked. If the frequency has not been successfully locked after a period of time, the voltage-controlled oscillation is adjusted Switch to the adjacent frequency band and restart the frequency lock until the frequency lock is successful, then set in this frequency band. Since the frequency lock detector operates at the comparison frequency, its speed is slower.

The frequency synthesizer proposed in US 6,747,519 uses the method of comparing voltages for rough adjustment. If the control voltage of the voltage controlled oscillator still exceeds the preset voltage range after a period of time, it means that the frequency lock has not been successful, and the voltage controlled oscillator is adjusted to The adjacent frequency band, restart the frequency lock, until the frequency lock is successful, it is set in this frequency band. This device often needs to try many frequency bands to successfully lock the frequency; moreover, compared to analog voltage signals, it is susceptible to process variations.

Although these two patents propose feasible frequency locking methods, it is necessary to wait for a period of time for the frequency synthesizer to lock the frequency to determine whether the currently selected frequency band is correct. Therefore, it takes a longer time to complete the coarse adjustment. For applications in frequency synthesis It is not feasible in a time-critical system.

In view of the problems of the conventional technology, the present invention proposes an automatic correction frequency synthesis device.

The purpose of the present invention is to provide a frequency synthesizer that can quickly complete rough adjustment, is suitable for high-speed operation, and is not affected by process variation.

The automatic correction frequency synthesis device proposed by the present invention is used to synthesize signals of a predetermined frequency, including: voltage controlled oscillator, pre-frequency division unit, feedback frequency division unit, automatic correction unit, phase frequency comparator, low-pass filter Device.

The voltage controlled oscillator has a plurality of working frequency bands, receives the coarse adjustment signal and the fine adjustment signal, and generates an output signal in the working frequency band set by the coarse adjustment signal. The pre-frequency division unit receives the output signal of the voltage-controlled oscillator, and generates an intermediate signal through frequency division. The feedback frequency elimination unit receives the intermediate signal and generates a feedback signal through frequency elimination. The automatic correction unit receives the input signal and the intermediate signal, and generates a coarse adjustment signal. The phase frequency comparator compares the input signal with the feedback signal, and generates an error signal according to the frequency and phase difference between the input signal and the feedback signal. The low-pass filter filters the error signal to generate a fine-tuning signal.

If the operating frequency of the automatic correction unit is high enough, the pre-frequency dividing unit can be omitted and the output signal can be directly received.

With regard to the features and implementation of the present invention, the preferred embodiments are described in detail as follows in conjunction with the drawings.

Specific embodiments are listed below to illustrate the content of the present invention in detail, and the figures are used as an auxiliary description. The symbols mentioned in the description refer to the schematic symbols.

Please refer to Figure 2 for the first embodiment of the present invention.

The automatic correction frequency synthesis device includes: a voltage-controlled oscillator 120, a pre-frequency division unit 130, a feedback frequency division unit 140, an automatic correction unit 160, and a phase frequency comparator 180.

The voltage controlled oscillator 120 has a plurality of working frequency bands, and the working frequency bands may or may not overlap. The voltage controlled oscillator 120 receives the coarse adjustment signal and the fine adjustment signal, and generates an output signal in the working frequency band set by the coarse adjustment signal.

The coarse adjustment signal is an N-bit digital signal, and the fine adjustment signal is an analog signal.

The pre-frequency division unit 130 receives the output signal, and generates an intermediate signal through frequency division.

The feedback frequency elimination unit 140 receives the intermediate signal, and generates a feedback signal through frequency elimination.

The automatic correction unit 160 receives the input signal and the intermediate signal, and generates a coarse adjustment signal.

The automatic correction unit 160 includes an accumulator 162, an arithmetic unit 164, and a control unit 166.

The accumulator 162 takes the intermediate signal as an input, calculates the number of periods of the intermediate signal in a period of the comparison signal, and obtains the frequency of the intermediate signal.

The arithmetic unit 164 calculates the working frequency band to which the predetermined frequency belongs based on the first frequency and the second frequency.

The control unit 166 is connected to the arithmetic unit 164 for generating a coarse adjustment control signal.

The phase frequency comparator 180 compares the input signal and the feedback signal, and generates an error signal according to the frequency and phase difference between the input signal and the feedback signal, and the fine-tuning signal is generated according to the error signal.

The low-pass filter 190 is connected between the phase frequency comparator 180 and the voltage-controlled oscillator 120, and receives the error signal to generate a fine-tuning signal.

The switch 170 is switched so that the voltage-controlled oscillator 120 is connected to the low-pass filter 190 or the fixed voltage VC. When the voltage-controlled oscillator 120 is connected to the low-pass filter 190, the voltage-controlled oscillator 120 receives the fine-tuning signal from the low-pass filter 190. When the voltage controlled oscillator 120 is connected to the fixed voltage VC, the fine-tuning signal is the fixed voltage VC. The switch 170 is controlled by the switch control signal generated by the automatic calibration unit 160.

The frequency lock operation of the frequency synthesis device is divided into four stages.

In the first stage, the switch control signal generated by the automatic correction unit 160 controls the analog input terminal of the voltage-controlled oscillator 120 to connect to a fixed voltage VC, and the coarse adjustment signal of the automatic correction unit 160 sets the voltage-controlled oscillator 120 to a frequency band. The accumulator 162 and the calculation unit 164 perform calculations to obtain the first frequency.

In the second stage, the coarse adjustment signal of the automatic correction unit 160 sets the voltage-controlled oscillator 120 to another frequency band, and the accumulator 162 and the arithmetic unit 164 perform calculations to obtain the second frequency.

In the third stage, the control unit 166 will judge according to the predetermined frequency of the desired frequency lock and the calculation result of the arithmetic unit 164, and output an appropriate N-bit digital control signal to the voltage controlled oscillator 120 to determine the voltage The appropriate operating frequency band of the controlled oscillator 120.

In the fourth stage, the automatic correction unit 160 connects the analog input terminal of the voltage-controlled oscillator back to the low-pass filter 190, so that the frequency synthesizer enters the frequency lock state.

Please refer to Figure 3 for the characteristic curve of the voltage controlled oscillator.

For example, in the first stage, the frequency band of the voltage-controlled oscillator 120 is set to S=1 and the first frequency is obtained as freq1, and in the second stage, the frequency band of the voltage-controlled oscillator 120 is set to S=8 and the second frequency is obtained as freq8. Because the characteristic curves of the voltage-controlled oscillator have the same interval, frequencies such as freq1 to freq8 can be obtained by interpolation, and the working frequency band to which the predetermined frequency belongs can be obtained.

For example, in the first stage, the frequency band of the voltage-controlled oscillator 120 is set to S=1 and the first frequency is obtained as freq1, and in the second stage, the frequency band of the voltage-controlled oscillator 120 is set to S=2 and the second frequency is obtained as freq2. Because the characteristic curves of the voltage-controlled oscillator have the same interval, frequencies such as freq1 to freq8 can be obtained by extrapolation, and the working frequency band to which the predetermined frequency belongs can be obtained.

Please refer to Figure 4 for the second embodiment of the present invention.

The automatic correction frequency synthesis device includes: a voltage controlled oscillator 120, a feedback frequency elimination unit 140, an automatic correction unit 160, and a phase frequency comparator 180.

The main difference between the second embodiment and the first embodiment is that the pre-frequency dividing unit is omitted. The automatic correction unit 160 directly receives the output signal. The feedback frequency divider 140 also directly receives the output signal. This embodiment is suitable for a system where the automatic correction unit can operate at a high enough frequency.

The automatic correction unit 160 receives the input signal and the output signal, and generates a coarse adjustment signal.

The automatic correction unit 160 includes an accumulator 162, an arithmetic unit 164, and a control unit 166.

The accumulator 162 takes the output signal as input, calculates the number of periods of the intermediate signal in a period of the comparison signal, and obtains the frequency of the intermediate signal.

The arithmetic unit 164 calculates the working frequency band to which the predetermined frequency belongs based on the first frequency and the second frequency.

The control unit 166 is connected to the arithmetic unit 164 for generating a coarse adjustment control signal.

The feedback frequency elimination unit 140 receives the output signal, and generates a feedback signal through frequency elimination.

Although the present invention is disclosed in the foregoing preferred embodiments as above, it is not intended to limit the present invention. Anyone familiar with similar art can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of patent protection for inventions shall be determined by the scope of patent applications attached to this specification.

<p>120. . . Voltage controlled oscillator</p><p>130. . . Pre-divider unit</p><p>140. . . Feedback frequency elimination unit</p><p>160. . . Automatic correction unit</p><p>162. . . accumulator</p><p>164. . . Arithmetic unit</p><p>166. . . control unit</p><p>170. . . Toggle switch</p><p>180. . . Phase frequency comparator</p><p>190. . . Low pass filter</p><p>200. . . Frequency divider</p><p>300. . . Phase detector</p>

Figure 1 is a frequency synthesizer of the prior art.

Figure 2 illustrates the first embodiment of the present invention.

Figure 3 is the characteristic curve diagram of the voltage controlled oscillator.

Figure 4 illustrates the second embodiment of the present invention.