Analog base band unit for a RF receiver and method for using the same

• US 20030017815A1
• Filed: 06/19/2002
• Published: 01/23/2003
• Est. Priority Date: 06/19/2001
• Status: Active Grant

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America), U-Blox AG (u-blox Holding AG)
• Original Assignee: Mu-Blox AG
• Inventors: Spiegel, Solon
• Granted Patent: US 7,065,336 B2
• Time in Patent Office: Days
• US Class Current: 455/234.1
• CPC Class Codes: H03G 1/04 Modifications of control circuit to reduce distortion caused by control modifications to reduce influence of variations of internal impedance of amplifying elements caused by control H03F1/08
• CPC Class Codes: H03G 3/30 in amplifiers having semiconductor devices
• CPC Class Codes: H03G 3/3052 in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver H03G3/32, H03G3/34 take precedence

Abstract

A feedback circuit for amplification of the output signal of an analog front end and suppression of its DC and low frequency components comprises a variable gain amplification unit (2) controlled by a gain control signal and a reverse path unit (6) comprising a filter unit (8) with variable time constant. A control unit (13) produces the gain control signal as well as a reverse path control signal (S) which causes adaptation of variable resistances (12) and capacitances (10) in such a way that the time constant of the filter unit (8) varies essentially proportionally with the gain of the variable amplifier unit (2). Thereby the gain of the feedback circuit as a function of the frequency retains its shape with varying gain. As the reverse path control signal (S) can be produced from different inputs selectable by selectors (20a, 20b) in the control unit (13) and due to the adaptability of the reverse path unit (6) and other features the analog base band unit is suited for the processing of signals of various types, e.g. signals pertaining to GPS and mobile telecommunication systems.

Claims

1. Analog base band unit for a RF receiver with a feedback circuit comprising a variable gain amplifier unit (2) whose gain is set depending on a gain control signal derived from its output signal and a reverse path unit (6) connecting the output of the variable gain amplifier unit (2) with its input, characterized in that it further comprises a control unit (13) for controlling at least one time constant of the reverse path unit (6) dependent on the gain.

2. Analog base band unit according to claim 1, characterized in that the at least one time constant is controllable in such a way that it varies approximately proportionally with the gain.

3. Analog base band unit according to claim 1 or 2, characterized in that the variable gain amplifier unit (2) is a variable gain amplifier chain made up of Gilbert cells or of amplification cells comprising operational amplifiers and switching networks.

4. Analog base band unit according to one of claims 1 to 3, characterized in that the reverse path unit (6) comprises a filter network (8) defining the at least one time constant of the reverse path unit (6).

5. Analog base band unit according to claim 4, characterized in that the filter network (8) comprises at least one variable resistance (10) controllable by the control unit (13).

6. Analog base band unit according to claim 5, characterized in that the variable resistance (10) comprises several resistors (23a-23d, 23a′

-23d′

), at least part of them each in series with at least one switch (24a-e, 24a′

-e′

) controllable by the control unit (13).

7. Analog base band unit according to one of claims 4 to 6, characterized in that the filter network (8) comprises at least one variable capacitance (12) controllable by the control unit (13).

8. Analog base band unit according to claim 7, characterized in that the at least one variable capacitance (12) comprises several capacitors (26a, 26b, 26a′

, 26b′

), at least part of them in series each with at least one switch (27a, 27b, 27a, 27b′

) controllable by the control unit (13).

9. Analog base band unit according to claim 7 or 8, characterized in that the variable capacitance (12) is part of a local feedback loop comprising an operational amplifier (11).

10. Analog base band unit according to one of claims 1 to 9, characterized in that the control unit (13) comprises a quantizer (15) comparing an input signal voltage (V_c) with several reference voltages (V_r1-V_r4) and providing digital output signals (A₁-A₄), each reflecting the result of one of the voltage comparisons and a decoder (16) for processing the said digital signals to provide at least part of a reverse path control signal (S) for controlling the time constant of the reverse path unit (6).

11. Analog base band unit according to one of claims 1 to 10, characterized in that the control unit (13) comprises an integrator (14).

12. Analog base band unit according to claim 11, characterized in that the integrator (14) has a speed-up input (19) for receiving a speed-up signal.

13. Analog base band unit according to one of claims 1 to 12, characterized in that it comprises a selector (20a) for connecting one of several inputs of the control unit (13) to further components of the same.

14. Analog base band unit according to claim 13, characterized in that it comprises a first monitoring unit connected between the output of the variable gain amplifier unit (2) and a first input of the selector (20a).

15. Analog base band unit according to claim 14, characterized in that the first monitoring unit is a synchronous AM detector (21).

16. Analog base band unit according to one of claims 1 to 15, characterized in that it comprises an A/D converter (3) for converting the output signal of the variable gain amplifier unit (6) to a digital signal.

17. Analog base band unit according to one of claims 13 to 15 and claim 16, characterized in that it further comprises a second monitoring unit connected between the output of the A/D converter (3) and a second input of the selector (20a).

18. Analog base band unit according to claim 17, characterized in that the second monitoring unit comprises a D/A converter or a logic control unit (22).

19. Analog base band unit according to one of claims 7 to 18, characterized in that it comprises at least one switch (27a, 27a′

) controllable by a burst control signal to shut off the at least one variable capacitance (12) in the reverse path unit (6).

20. Analog base band unit according to one of claims 1 to 19, characterized in that it comprises a low pass filter unit (1) preceding the variable gain amplifier unit (2).

21. Method for using an analog base band unit according to one of claims 1 to 20 to process a GPS signal, characterized in that the analog base band unit is controlled so as to process the signal with an acquisition bandwidth during a signal acquisition phase and with a larger tracking bandwidth during a subsequent signal tracking phase.

22. Method according to claim 21, characterized in that the tracking bandwidth is at least twice the acquisition bandwidth.