Apparatus and method for phase lock loop gain control

• US 7,397,319 B2
• Filed: 06/25/2007
• Issued: 07/08/2008
• Est. Priority Date: 03/20/2001
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Gomez, Ramon A.
• Primary Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US11/767,899
• Publication Number:
  US 20070247238A1
• Time in Patent Office: 379 Days
• Field of Search: 331/2, 331/16, 331/36.C, 331/179, 331/177.V, 331/34
• US Class Current: 331/179
• CPC Class Codes: H03B 2200/0046 including measures to switch the gain of an amplifier
• CPC Class Codes: H03B 2200/0048 including measures to switch the frequency band, e.g. by harmonic selection
• CPC Class Codes: H03B 2200/005 including measures to switch a capacitor
• CPC Class Codes: H03B 2201/02 Varying the frequency of the oscillations by electronic means
• CPC Class Codes: H03B 2201/0208 the means being an element with a variable capacitance, e.g. capacitance diode
• CPC Class Codes: H03B 2201/025 the means being an electronic switch for switching in or out oscillator elements
• CPC Class Codes: H03B 5/1212 the amplifier comprising a pair of transistors, wherein an output terminal of each being connected to an input terminal of the other, e.g. a cross coupled pair
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/1243 the means comprising voltage variable capacitance diodes
• CPC Class Codes: H03B 5/1253 the transistors being field-effect transistors
• CPC Class Codes: H03B 5/1265 switched capacitors
• CPC Class Codes: H03B 5/1278 the parameter being an amplitude of a signal, e.g. maintaining a constant output amplitude over the frequency range
• CPC Class Codes: H03D 7/165 at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature combined with amplitude demodulation H03D1/2245, combined with angle demodulation H03D3/007; N-path filters H03H19/002
• CPC Class Codes: H03D 7/18 Modifications of frequency-changers for eliminating image frequencies H03D7/16 takes precedence
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03J 5/244 using electronic means
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation
• CPC Class Codes: H03L 7/0898 the source or sink current values being variable H03L7/0896 takes precedence
• CPC Class Codes: H03L 7/093 using special filtering or amplification characteristics in the loop H03L7/087 - H03L7/091 take precedence
• CPC Class Codes: H03L 7/099 : concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/1072 : by changing characteristics of the charge pump, e.g. changing the gain
• CPC Class Codes: H03L 7/18 : using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence

Abstract

A gain compensator compensates for the gain variation of a varactor-tuned voltage tuned oscillator (VCO) in a phase lock loop (PLL). The VCO includes a parallel LC circuit having multiple fixed capacitors that can be switched-in or switched-out of the LC circuit according to a capacitor control signal to perform band-select tuning of the VCO. The gain compensator compensates for the variable VCO gain by generating a charge pump reference current that is based on the same capacitor control signal that controls the fixed capacitors in the LC circuit. The gain compensator generates the charge pump reference current by replicating a reference scale current using unit current sources. The number of times the reference scale current is replicated is based on the fixed capacitance that is switched-in to the LC circuit and therefore the frequency band of the PLL. The reference scale current is generated based on a PLL control that specifics certain PLL characteristics such as reference frequency, loop bandwidth, and loop damping. Therefore, the reference pump current can be efficiently optimized for-changing PLL operating conditions, in addition to compensating for variable VCO gain.

Claims

1. A system for compensating the gain of a phase lock loop (PLL), comprising:

a plurality of voltage controlled oscillators (VCOs) operatively coupled to a plurality of gain compensator cells, each VCO corresponding to a respective gain compensator cell,

wherein the VCOs are operatively coupled to a tuning circuit, the VCOs being tuned by the tuning circuit, the tuning circuit adding or removing capacitance according to a capacitance control signal, and

wherein at least one gain compensator cell comprises switches and current groups, the switches being operatively coupled to the current groups, the switches being operatively coupled to the capacitance control signal, each current group corresponding to a respective switch, each current group comprising a plurality of identical current sources, the identical current sources of each current group being configured in a current mirror arrangement, each current group being operatively coupled to a voltage, the voltage being a function of one or more PLL characteristics.

2. The system according to claim 1, wherein one of the VCOs is selected at a time.

3. The system according to claim 2, wherein each current group is operatively coupled to the voltage through the respective switch.

4. The system according to claim 2, wherein the capacitance control signal determines which of the current groups receives the voltage.

5. The system according to claim 3, wherein the current groups that receive the voltage generate current that is summed.

6. The system according to claim 5, wherein the summed current is used to compensate for the gain of the PLL.

7. The system according to claim 2, wherein the selected VCO is selected a VCO selection signal.

8. The system according to claim 7, wherein the VCO selection signal selects the respective gain compensation cell.

9. The system according to 2, wherein the capacitance control signal controls the switches.

10. The system according to claim 1, comprising:

a voltage generator operatively coupled to the gain compensator cells,

wherein the voltage generator generates the voltage based on a PLL control signal.

11. The system according to claim 10, wherein, in generating the voltage, the voltage generator weights different PLL characteristics provided by the PLL control signal.

12. The system according to claim 11, wherein the different PLL characteristics comprise two or more of the following:

PLL bandwidth, PLL damping factor, loop bandwidth and loop damping factor and frequency of PLL reference signal.

13. The system according to claim 10, wherein, in generating the voltage, the voltage generator combines contributions from different PLL characteristics.

14. The system according to claim 13, wherein the different PLL characteristics comprise two or more of the following:

PLL bandwidth, PLL damping factor, loop bandwidth and loop damping factor and frequency of PLL reference signal.

15. The system according to claim 1, wherein the one or more PLL characteristics comprises one or more of the following:

PLL bandwidth, PLL damping factor, loop bandwidth and loop damping factor and frequency of PLL reference signal.

16. The system according to claim 1, wherein the identical current sources comprise field effect transistors (FETs).

17. The system according to claim 2, wherein the identical current sources comprise FETs.

18. The system according to claim 1, wherein the voltage is generated by a voltage generator, the voltage generator comprising weighted current sources.

19. The system according to claim 2, wherein the voltage is generated by a voltage generator, the voltage generator comprising weighted current sources.

20. The system according to claim 19, wherein the voltage generator comprises a FET operatively coupled to the weighted current sources.