Methods and Systems for Production Testing of DCO Capacitors

• US 20120112768A1
• Filed: 05/19/2011
• Published: 05/10/2012
• Est. Priority Date: 11/10/2010
• Status: Active Grant

• Current Assignee: ST-Ericcson SA (Telefonaktiebolaget LM Ericsson)
• Original Assignee: ST-Ericcson SA (Telefonaktiebolaget LM Ericsson)
• Inventors: KUENEN, Jeroen
• Granted Patent: US 8,760,176 B2
• Time in Patent Office: Days
• US Class Current: 324/647
• CPC Class Codes: G01R 23/00 Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
• CPC Class Codes: G01R 23/09 using analogue integrators, e.g. capacitors establishing a mean value by balance of input signals and defined discharge signals or leakage
• CPC Class Codes: G01R 27/04 in circuits having distributed constants , e.g. having very long conductors or involving high frequencies
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G01R 27/32 in circuits having distributed constants , e.g. having very long conductors or involving high frequencies
• CPC Class Codes: G01R 31/2824 testing of oscillators or resonators
• CPC Class Codes: G01R 31/31727 Clock circuits aspects, e.g. test clock circuit details, timing aspects for signal generation, circuits for testing clocks G01R31/31725 takes precedence; concerning scan test G01R31/318552, for tester hardware G01R31/31922
• CPC Class Codes: H03L 2207/50 All digital phase-locked loop
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop

Abstract

Systems provide for a test system for capacitors in a digitally controllable oscillator (DCO). The system includes: capacitor toggling logic configured to switch on and off a selected one of the capacitors at a modulation frequency; a tone generator configured to generate a tone; a mixer configured to receive the tone and an output carrier signal from the DCO while the capacitor toggling logic is switching the selected one of the capacitors on and off and to output an intermediate frequency signal having FM sidebands based on the modulation frequency and relative capacitor size; and an evaluation circuit configured to evaluate a frequency deviation associated with the selected one of the capacitors based on at least one of the FM sidebands.

Claims

1. A test system for capacitors in a digitally controllable oscillator (DCO) comprising:

capacitor toggling logic configured to switch on and off a selected one of the capacitors at a modulation frequency;

a tone generator configured to generate a tone;

a mixer configured to receive the tone and an output carrier signal from the DCO while the capacitor toggling logic is switching the selected one of the capacitors on and off, and to output an intermediate frequency signal having FM sidebands based on the modulation frequency and relative capacitor size; and

an evaluation circuit configured to evaluate a frequency deviation associated with the selected one of the capacitors based on at least one of the FM sidebands.

2. The test system of claim 1, wherein the modulation frequency is generated by using a frequency source which is independent of the DCO.

3. The test system of claim 1, wherein the selected one of the capacitors is switched on and off when conditions of an XOR gate and an AND gate are met.

4. The method of claim 3, wherein selecting of the first capacitor is performed by a decoder.

5. The test system of claim 1, wherein the modulation frequency is selected such that a measured FM sideband value is approximately −

20 dBc.

7. The method of claim 1, further comprising:

generating the modulation frequency by dividing a frequency of the DCO by a divider.

8. The method of claim 7, further comprising:

deselecting the first capacitor; and

selecting a second capacitor.

9. The method of claim 8, wherein when the second capacitor has a different capacitance from the first capacitor the value of the divider is changed such that the FM sideband level remain substantially unchanged.

6. A method for testing a plurality of capacitors within a digital controllable oscillator (DCO), the method comprising:

selecting a first capacitor of the plurality of capacitors to be tested;

generating a carrier signal from the DCO while switching the first capacitor on and off at a modulation frequency;

mixing the carrier signal from the DCO with a test signal to generate an intermediate frequency (IF) signal; and

determining a relative sideband level associated with a frequency modulated (FM) IF signal.

10. The method of claim 6, further comprising:

generating the modulation frequency using a frequency source which is independent of the DCO.

11. The method of claim 6, wherein the selected first capacitor is switched on and off when conditions of an XOR gate and an AND gate are met.

12. The method of claim 11, wherein selecting of the first capacitor is performed by a decoder.

13. The method of claim 6, wherein the modulation frequency is selected such that a measured FM sideband value is approximately −

20 dBc.

14. A digital controllable oscillator (DCO) manufactured by the process comprising the steps of:

selecting a first capacitor of the plurality of capacitors to be tested;

generating an output signal from the DCO associated with the first capacitor;

mixing the output signal from the DCO with a test signal; and

evaluating a frequency deviation of a frequency modulated (FM) sideband of the first capacitor.

15. The DCO manufactured by the process of claim 14, wherein the process further comprises:

generating the modulation frequency by dividing a frequency of the DCO by a divider.

16. The DCO manufactured by the process of claim 15, wherein the process further comprises:

deselecting the first capacitor; and

selecting a second capacitor.

17. The DCO manufactured by the process of claim 16, wherein when the second capacitor has a different capacitance from the first capacitor the value of the divider is changed such that the FM sideband level remains substantially unchanged.

18. The DCO manufactured by the process of claim 14, wherein the process further comprises:

generating the modulation frequency using a frequency source which is independent of the DCO.

19. The DCO manufactured by the process of claim 14, wherein the selected first capacitor is switched on and off when conditions of an XOR gate and an AND gate are met.

20. The DCO manufactured by the process of claim 19, wherein selecting of the first capacitor is performed by a decoder.