KR19990006583A - Apparatus and tuning method for voltage controlled oscillators - Google Patents

Abstract

The method of tuning the voltage controlled oscillator (VCO) includes initializing the programmable voltage and applying the programmable voltage to the VCO to tune the VCO 502. A control voltage is applied to the VCO to lock the VCO, and the VCO is checked to determine if it is in the locked state 504. If the VCO is locked, the control voltage is measured and compared with the selected voltage range. If it is detected that the VCO is not locked or if the control voltage is not within the predetermined voltage range, adjust the programmable voltage and repeat the steps until the VCO is locked to the control voltage within the selected control voltage range.

Description

Apparatus and tuning method for voltage controlled oscillators

The present invention relates generally to voltage controlled oscillators, and more particularly to tuning of voltage controlled oscillators.

Voltage controlled oscillator (VCO) circuits are used in communication devices as a means of generating a predetermined operating frequency. It is typically necessary to tune the VCO as part of a phase lock loop (PLL) circuit so that the communication device locks at a given frequency. This tuning process typically requires manual tuning or laser trimming of the tuning capacitors in the VCO circuit. 1 shows a prior art Colpitts VCO circuit 100 including a trim capacitor 102. Trim capacitor 102 controls the tuning of tank circuitry 104 while active circuit 106 generates a radio frequency (RF) output. Some problems may arise during the manufacturing of VCOs using trim capacitors, especially in wireless manufacturing environments. For example, laser trimming or manual tuning of trim capacitor 102 is required to lock the VCO to a predetermined frequency. Trimming or tuning is very costly in terms of production time and cost, as well as equipment, test software, and human resources. The maintenance and rework of incorrectly laser trimmed parts as well as the maintenance of the laser equipment itself can be costly.

In the past, one way to correct the tuning problem of VCOs in a wireless environment has been to eliminate frequency tuning by designing the VCO frequency to a wider band than is required. However, the disadvantage of increasing the VCO band is that it is much larger than it requires Ko (the VCO gain parameter measured in MHz / V). This large Ko compromises the VCO's electrical performance, resulting in poor wireless performance. For example, the PLL loop filter response and ability for balanced modulation can be counterproductive. The resulting VCO has sideband noise and hum-to-noise performance worse than the frequency-tuned VCO. This degraded VCO parameter results in reduced adjacent channel and hum noise performance in the radio in both transmit and receive modes.

In addition, many tuning operations in today's factories still require direct frequency measurements from the radio during the tuning process. This often requires the use of additional equipment, such as spectrum analyzers, in a manufacturing environment.

Accordingly, there is a need for improved VCO and VCO tuning techniques while eliminating manual tuning or laser trim tuning of the VCO.

Therefore, the voltage controlled oscillator (VCO) circuit of the present invention comprises the steps of: initializing a programmable voltage; Applying a programmable voltage to the VCO to tune the VCO; Applying a control voltage to the VCO to lock the VCO; Determining whether the VCO is locked; Measuring a control voltage to determine if the VCO is in a locked state; Comparing the control voltage with a predetermined range; Adjusting the programmable voltage whether the VCO is in a locked state or the control voltage is not within the predetermined range; And repeating the determining, measuring, comparing, and adjusting steps until the VCO is locked and the control voltage is within a predetermined range.

1 shows a voltage controlled oscillator of the prior art;

2 is a block diagram of a PLL in accordance with the present invention.

3 is a block diagram of the VCO of FIG. 2 in accordance with the present invention;

4 is a circuit diagram of a VCO in accordance with a preferred embodiment of the present invention.

5 is a flow chart of a VCO tuning technique in accordance with the present invention.

6 is a graph showing an example of a response representing Ko versus control voltage for a VCO in accordance with the present invention.

Explanation of symbols for the main parts of the drawings

202: reference input

204: phase detector

210: loop filter

214: voltage controlled oscillator

218: D / A Converter

220: microprocessor

222 loop divider

Although the specification concludes with the claims, which define the features of the invention, which are considered to be novel, the invention will be better understood upon consideration of the following description with reference to the drawings, wherein like reference numerals are assigned.

The VCO apparatus and tuning technique, detailed herein, provide a narrower band VCO that achieves improved communication performance in wireless products without the disadvantages of the tuning technique previously described.

2, a block diagram of a PLL 200 as shown in a wireless communication product in accordance with the present invention is shown. PLL 200 receives a reference input signal 202 that is typically derived from a crystal controlled oscillator (not shown). The phase detector 204 compares the phase difference between the reference input 202 and the divided VCO frequency 206 to produce the error voltage 208. The error voltage 208 is filtered at the loop filter 210 to produce a DC signal to be referred to as the voltage control signal Vcont 212. The control voltage signal 212 is input to the VCO 214 to steer the frequency of the VCO. In accordance with the present invention, tuning of the VCO 214 is performed by checking the locked VCO state, such as through a lock detection circuit (not shown), and the adjustable programmable voltage (Vadj: 216) is set via external programming. This is done by monitoring the control voltage 212 during this drop. Programmable voltage 216 is preferably generated from the D / A converter under microprocessor 220 control. The output of the VCO (RF output) is divided by an integer N through a phase divider loop divider 222.

According to the present invention, the programmable voltage Vadj 216 is initialized to tune the VCO 214 to a predetermined predetermined operating frequency, while the control voltage 212 attempts to lock the VCO by frequency. Once the VCO locks to frequency, the control voltage 212 is preferably measured through the test point 224 and is preferably compared to a predetermined voltage range stored in the memory area of the microprocessor 220. If the control voltage Vcont 212 is within the selected range, the tuning of the VCO is complete. If the VCO fails to lock, the programmable voltage (Vadj: 216) is adjusted to a predetermined amount and the VCO will attempt to lock back to frequency. The D / A converter will continue to adjust the programmable voltage 216 until the VCO locks into frequency or reaches a predetermined programming voltage limit.

3 shows a simplified block diagram of the VCO 214 of FIG. 2 in accordance with the present invention. VCO 214 includes tank circuit 302 and active circuit 304. According to the present invention, the tank circuit 302 receives a programmable voltage (Vadj: 216) to tune the frequency of the VCO while the control voltage (Vcont) 212 attempts to lock the VCO.

4 shows a preferred embodiment of the VCO 214 in a Colpitts oscillator configuration as used in wireless. Programmable voltage 216 tunes tank circuit 302, preferably via a biasing circuit comprising choke 402, varactor 404, and capacitor 406. Other biasing circuit arrangements may also be implemented to tune the VCO through the tank circuit 302.

5, a flowchart 500 of a VCO tuning technique 500 in accordance with a preferred embodiment of the present invention is shown. In step 502, the programmable voltage is initialized to a value corresponding to a predetermined tuning frequency. This initialization step is preferably performed by the D / A converter 218. The VCO is then checked in step 504 to determine if the VCO is in a locked state (via lock detection or other means). If the VCO is locked, then the VCO control voltage Vcont is measured at step 506. Under the locked condition, the control voltage measured at step 506 is compared with a predetermined voltage range with upper and lower voltages to see if the readout value measured at step 508 is within a predetermined window. If the control voltage value is between the limits selected in step 508, then tuning progress is completed in step 510. If the VCO is not locked in step 504 or if the control voltage value in the locked state is not within the predetermined voltage limit of step 508, then in step 512 the programmable voltage is adjusted by a predetermined amount. Adjusting the programmable voltage is preferably performed by increasing or decreasing the D / A converter. The steps of judging, measuring, comparing, and adjusting are repeated until the VCO is locked and the control voltage is within a predetermined voltage range. Before adjusting the programmable voltage in step 512, the programmable voltage is preferably compared to the maximum voltage setting in step 514 where the VCO is considered to have failed the tuning procedure in step 516.

According to the present invention, there are several programmable voltage settings at which the VCO will be locked at the PLL. By monitoring the control voltage Vcont of the VCO under lock conditions for different values of such D / A programmable voltage Vadj, the optimal program voltage setting (or programming word) can be written to the wireless programming code. The final programmable voltage regulation (Vadj) setting will correspond to the control voltage value within the selected upper and lower limits.

Although the present invention has been shown and described above as a Colpitts oscillator, one of ordinary skill in the art will appreciate that the VCO 214 and VCO tuning techniques 500 described above by the present invention may be Hartley, Clap, and It can be seen that it can be widely applied to other oscillator configurations such as a pierce oscillator configuration.

The upper and lower control voltages are selected such that the final control voltage value is the result of predictable electrical performance for all radios that go through the tuning process 500 of the present invention. This is accomplished by setting such a control voltage limit so that the final value is substantially fixed and consistent with Ko and the response is within a known set range. An example of such a response is shown in FIG. 6. Graph 600 shows Ko (MHz / V) vs. VCO control voltage (V). For the curve shown in graph 600, the acceptable control voltage limit can be chosen to be about 1.1V (point 602) while the upper limit control voltage limit is acceptable to ensure the locked state of the VCO with a given Ko. It may be chosen to be about 2.3V (point 604) to provide a range of values. By keeping Ko within a reasonable range of the selected value, it helps to maintain most other radio circuit parameters and prevents the radio from deviating from the expected design response.

Thus, a VCO apparatus and tuning technique is provided that allows the VCO to be electronically frequency tuned during the wireless generation phase or the production phase of the transceiver product. The electronically tunable VCO described in accordance with the present invention reduces manufacturing problems associated with tuning and trimming of the VCO. Elimination of trim capacitors eliminates the need for manual tuning and laser trimming, saving both time and money. This minimizes repairs and rework and fundamentally eliminates all manual tuning. The electronically tunable VCO described above in accordance with the present invention also provides the added benefit of tuning the VCO in a closed loop system, eliminating the need for direct frequency measurements from the radio during tuning operation.

While preferred embodiments of the invention have been illustrated and described above, it is clear that the invention is not limited thereto. Numerous variations, changes, variations, substitutions and equivalents may occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims (10)

In the tuning method of a voltage controlled oscillator (VCO) circuit, Initializing the programmable voltage; Tuning the VCO by applying a programmable voltage to the VCO; Applying a control voltage to the VCO to lock the VCO; Determining whether the VCO is locked; Measuring a control voltage to determine if the VCO is in a locked state; Comparing the control voltage to a predetermined range; Adjusting the programmable voltage whether the VCO is in a locked state or the control voltage is not within the predetermined range; And Repeating the determining, measuring, comparing, and adjusting steps until the VCO is locked and the control voltage is within the predetermined range. VCO circuit tuning method comprising a. The method of claim 1, And said programming voltage is generated by a DA converter. The method of claim 2, And said adjusting step comprises increasing said D / A converter. The method of claim 2, And said adjusting step comprises reducing said D / A converter. In a method of optimizing tuning in a VCO circuit, Selecting a control voltage range for the VCO; Initializing a programmable voltage corresponding to the selected tuning frequency; Applying a control voltage to the VCO to lock the VCO at the predetermined tuning frequency; And Adjusting the tuning frequency through the programmable voltage until the VCO locks to a frequency at a control voltage within the predetermined control voltage range Method for optimizing the tuning in the VCO circuit comprising a. The method of claim 5, Increasing the adjustment step when the programming voltage exceeds a predetermined limit. In the programmable VCO, A tank circuit that receives a programmable voltage to tune the frequency of the VCO and a control voltage to lock the VCO onto the tuning frequency—the VCO is characterized by a Ko value, the Ko value Is determined by the VCO locking to a frequency with a control voltage within a predetermined limit; And An active circuit connected to the tank circuit and generating an RF output Programmable VCO comprising a. The method of claim 7, wherein The programmable voltage is generated from a DA converter. The method of claim 8, And the DA converter is under microprocessor control. In a phase lock loop, A VCO generating a radio frequency (RF) output and characterized by a Ko value; A phase detector for generating an error signal by comparing the reference frequency to the divided VCO frequency; A loop filter for filtering the error signal and providing a control voltage to steer the VCO, the VCO receiving an adjustable programmable voltage to tune the VCO to a predetermined operating frequency, wherein the VCO is characterized by a value of Ko And the Ko value is determined by the VCO locking to a frequency with a control voltage within a predetermined limit; And A divider for dividing the RF output into divided VCO frequencies Phase lock loop comprising a.