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Title:
RECEIVER HAVING A CALIBRATING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2004/093355
Kind Code:
A1
Abstract:
A calibrating system for a receiver receiving an input signal (Rf) having an input frequency (fRf) and working in a receiving mode (R) and in a calibrating mode (C) comprising an intermediate frequency circuit (IF) coupled to a first mixer and comprising a bulk acoustic wave filter (BAW) determining the intermediate frequency (BAWf). The calibrating system further comprises a level detecting circuit (LD) coupled to the intermediate frequency circuit (IF) via a first switch (S1) in the calibrating mode (C) for determining an amplitude of the intermediate frequency signal. The receiver includes a tuning control processor (TC) coupled to the first synthesizer (LO1) and to the second synthesizer (L02) controlling the frequencies generated by said synthesizers (LO1, L02). A level detecting circuit (LD) is coupled to the intermediate frequency circuit (IF) for determining an amplitude of the intermediate frequency signal and providing a signal indicative for said amplitude to the tuning control processor (TC). The system further comprises a register (Reg) coupled to the tuning control processor (TC) for memorizing a number corresponding to the intermediate frequency (BAWf), the number being used as a correction factor for the first and second synthesizers (LO I, L02) in the receiving mode (R).

Inventors:
VAUCHER CICERO S (NL)
STIKVOORT EDUARD F (NL)
Application Number:
PCT/IB2004/050413
Publication Date:
October 28, 2004
Filing Date:
April 08, 2004
Export Citation:
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Assignee:
KONINKL PHILIPS ELECTRONICS NV (NL)
VAUCHER CICERO S (NL)
STIKVOORT EDUARD F (NL)
International Classes:
H03J1/00; H03L7/16; H04B1/28; (IPC1-7): H04B17/00; H03J1/00; H03J7/04
Foreign References:
EP1253715A12002-10-30
Attorney, Agent or Firm:
Duijvestijn, Adrianus J. (AA Eindhoven, NL)
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Claims:
CLAIMS:
1. A receiver for receiving an input signal (Rf) having an input frequency (fRf) and having a receiving mode (R) and a calibrating mode (C), the receiver comprising a first mixer (Ml) coupled to receive the input signal (Rf) and a first signal generated by a first synthesizer (L01) for converting the input signal frequency (fla into an intermediate signal having a first intermediate frequency (BAWf), an intermediate frequency circuit (IF) coupled to the first mixer and comprising a filter (BAW) tuned to a frequency substantially equal to the intermediate frequency (BAWf), a second mixer (M2) coupled to receive a signal provided by the intermediate frequency circuit (IF) and a signal generated by a second frequency synthesizer (L02) and having a frequency substantially equal to the first intermediate frequency (BAWf), a tuning control processor (TC) coupled to the first synthesizer (L01) and to the second synthesizer (L02) controlling the frequencies generated by said synthesizers (L01, L02), a level detecting circuit (LD) coupled to the intermediate frequency circuit (IF) for determining an amplitude of the intermediate frequency signal and providing a signal indicative for said amplitude to the tuning control processor (TC), and a register (Reg) coupled to the tuning control processor (TC) for memorizing a number corresponding to the intermediate frequency (BAWf), the number being used as a correction factor for the first and second synthesizers (L01, L02) in the receiving mode (R).
2. A receiver as claimed in claim 1, wherein in the calibrating mode (C) the intermediate frequency circuit (IF) is coupled to the second frequency synthesizer (L02), and the second frequency synthesizer (L02) works in a sweeping mode for determining the intermediate frequency (BAWf).
3. A method of calibrating of a receiver as claimed in claim 2, the method comprising the steps of turning the receiver into the calibrating mode (C), sweeping a second synthesizer (L02) signal frequency, determining a maximum amplitude of the intermediate frequency signal (BAWf), and memorizing the number corresponding to the maximum amplitude of the intermediate signal in the register (Reg).
4. A receiver as claimed in claim 1, wherein in the calibrating mode a frequency divider (D) is coupled to an input of the receiver and to the first synthesizer (L01) via respective switch (S'), the frequency divider providing a divided signal (fOl) having a frequency that is an nth part of the frequency of the signal generated by the first synthesizer (fLOl), the divided signal (fOl) and the signal generated by the first synthesizer being mixed in the first mixer (Ml).
5. A method of calibrating a receiver as claimed in Claim 4, the method comprising steps of, turning the receiver into calibrating mode (C), sweeping a first synthesizer (LO1) signal frequency (fLOl), dividing by a number n the first synthesizer (LO1) signal frequency (fLOl), for obtaining a divided signal (fOl), mixing the divided signal (fDl) with the signal of the first synthesizer (LO1) for obtaining a signal having a frequency substantially equal to the intermediate frequency signal (BAWf), determining a maximum amplitude of the intermediate frequency signal (BAWf), memorizing the number corresponding to the maximum amplitude of the intermediate signal in the register (Reg),.
6. A receiver as claimed in claim 1, wherein the level detecting circuit (LD) comprises a level detector (1) coupled to a differentiation circuit (2) followed by a slicer (3).
7. A receiver as claimed in claim 6, wherein the level detector (1) is coupled to an automatic gain control amplifier (AGC) included in the intermediate frequency circuit (IF).
Description:
RECEIVER HAVING A CALIBRATING SYSTEM

The invention relates to a calibrating system for a receiver.

Receivers are wide spread devices used in various technical fields. Present application refers to receivers used in television applications and radio applications both analog and digital.

A block diagram of a prior art up-conversion tuner is shown in Figure 5. In this example, the channel filtering is done by a Bulk Acoustic Wave (BAW) filter, which replaces the conventional Surface Acoustic Wave (SAW) filter. The BAW filter is smaller than today's SAW filters and can be bumped to the die of a"semi-integrated"tuner. When compared to a"fully-integrated tuner"the BAW filter replaces the on-chip Radio Frequency (RF) and Intermediate Frequency (IF) filtering sections. That saves power dissipation and the die area of the integrated RF and IF filters.

In the circuit of Fig. 5 the RF input signal is converted into a balanced signal and forwarded to the mixer. The output signal of the mixer is amplified and given to the BAW filter, with a nominal center frequency BAWf of e. g. 1200 MHz and a bandwidth of 1 TV channel of about 8 MHz. The BAW filter determines the channel selectivity. For reception of a RF signal at frequency fRf, the frequency of the first local oscillator signal f must be set to: fLo= fRf + BAW£ (1) The output signal of the BAW filter passes through the Automatic Gain Control amplifier (AGC) and is down-converted by the second mixer. The second local oscillator signal has a frequency of flein the case of analog TV, as shown in Fig. 5, the down-conversion is the demodulation (picture carrier to dc). In this case the following relation holds for fLO2 : IL02-BAWf-foffcamer, (2) foffcarrier being offset frequency of the picture carrier with respect to the center frequency of the BAW filter. A polyphase filter implements the Nyquist slope filtering and provides an additional suppression of the lower neighbor.

For digital TV reception zero-IF down-conversion may be used, as depicted in Figure 6. In this application, the frequency fLo2 should be set to: fLo2= BAWf

A bottle-neck related to the system concepts depicted in Figs. 5 and 6 is that the center frequency BAWf of the BAW filter is subject to production spread, which can be in the order of several times its bandwidth. Note, however, from Equations (1), (2) and (3) that knowledge of BAWf is required for the tuning and demodulation operations.

US-A-6, 051,907 describes a method for tuning Thin Film Bulk Acoustic Wave Resonator located on a wafer. A first step of the method includes measuring a frequency at which the resonator exhibits a resonance. As a consequence, next steps provide the necessary information and methods to modify the geometrical properties of the resonator such that an error of the resonance frequency of the resonators on the wafer is below certain value e. g. 1%. Let us observe that assuming a 1% error in resonant frequency of the resonator conducts for certain intermediate frequencies in a receiver to errors that are not tolerable e. g. larger that a bandwidth of a TV channel i. e. 8 MHz. Indeed, considering a 1% error for a resonator working at 1200 MHz results in an error of 12 MHz, which is larger that 8 MHz.

Furthermore, trimming a ready made resonator in a receiver is not practically possible.

The standard solution for the problem is to perform"test-bench"measurements on each manufactured tuner, in order to find the frequency BAWf in an experimental way.

The value may then be stored in a non-volatile memory as an EPROM, or given it to the TV set manufacturer in"written-on-paper"format. Such a solution has serious drawbacks, such as a long test time at the tuner manufacturer, which decreases the profitability of the product, and the added cost of the EPROM or the additional logistic problems associated with "written-on-paper"formats. Besides, this method can not account for long-term shift in the center frequency of the BAW filter caused by aging, neither frequency shifts due to temperature variations.

It is therefore an object of present invention to overcome the above-mentioned problems. The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

It is considered ab initio that the first and the second frequency synthesizers provide signals whose frequency is controlled by digital signals provided by e. g. an internal processor or an external processor via an adequate interface protocol as e. g. I2C. Hereinafter said processor is named tuning control processor. It is also mentioned that the intermediate

frequency circuit has a band-pass characteristic centered on the intermediate frequency and therefore when an input signal has a frequency substantially equal with the intermediate frequency the signal provided by the intermediate frequency circuit has a maximum amplitude value. Hence, intermediate frequency circuit behaves as a maximum detector in the calibrating mode.

In an embodiment of the calibrating system the level detecting circuit comprises a level detector coupled to a differentiation circuit followed by a slicer. The level detector is coupled to an automatic gain control amplifier included in the intermediate frequency circuit.

The output level of the intermediate frequency circuit is detected by the level detector that may be a part of the intermediate frequency circuit, the level detector being coupled to an automatic gain control circuit (AGC) amplifier. The frequency for which the AGC setting is for the smallest gain is stored.

In another embodiment of the invention the intermediate frequency circuit is coupled to the second frequency synthesizer in the calibrating mode, the second frequency synthesizer working in a sweeping mode for determining the intermediate frequency, a binary number corresponding to the intermediate frequency being memorized in the register. During initialization the frequency of the second synthesizer is swept step-wise from a minimum value to a maximum value e. g. from 1100 MHz till 1300 MHz if the intermediate frequency is 1200 MHz. Recall that the frequency is binary controlled. With increasing frequency the output level of the intermediate frequency signal increases, so that at each step of a controller controlling the second synthesizer the register receives a clock pulse. When the maximum has been passed, the pulses are negative and the register does not receives any clock pulse from the tuning control processor. With this algorithm the frequency with maximum transfer of the BAW filter is stored.

As it was explained above, the simplest way to carry out the calibration is using the second synthesizer as a sweeping generator but it may be carried out using an external sweeping generator controlled by a processor.

In an embodiment of the invention in a calibrating mode a frequency divider is coupled to an input of the receiver and to the first synthesizer via respective switches, the frequency divider providing a divided signal having a frequency that is n-th part of the frequency of the signal generated by the first synthesizer, the divided signal and the signal generated by the first synthesizer being mixed up in the first mixer, the Register being coupled to a second divider performing a n/ (n-l) division of the binary number memorized in

the register and providing a binary number being indicative for the first intermediate frequency. After the first mixer, the signal has a frequency that equals (n-1)/n of the frequency generated by the first synthesizer and this frequency has to be in the intermediate frequency band. For example, if the frequency generated by the first synthesizer is 1700 MHz and the intermediate frequency is 1200 MHz it results that n should be 3.

The above-mentioned calibration may be carried out in a sequential manner, with method steps that may be in form of a computer program controlling the first frequency synthesizer and the switches. The communication between the processor running the program and the synthesizer may be implemented with standard protocols as e. g. I2C.

The above and other features of the invention will be apparent from the following description of the exemplary embodiments of the invention with reference to the accompanying drawings, in which: Fig. 1 depicts a block schematic of a receiver comprising a calibrating system according to a first embodiment of the invention, Fig. 2 depicts a block schematic of a receiver comprising a calibrating system according to a second embodiment of the invention, Fig. 3 depicts a more detailed description of a level detection circuit for use in a receiver according to the invention, Fig. 4 depicts a more detailed description of an intermediate frequency circuit for use in a receiver according to the invention, Fig. 5 depicts a prior-art analog receiver, and Fig. 6 depicts a prior-art digital receiver.

Fig. 1 depicts a block schematic of a calibrating system according to a first embodiment of the invention. The calibrating system is designated for a receiver receiving an input signal Rf having an input frequency fRf and working in a receiving mode R and in a calibrating mode C. The calibrating system comprises a first mixer Ml receiving the input signal Rf and a first signal generated by a first synthesizer LO1 for converting the input signal frequency fRf in an intermediate signal having a first intermediate frequency BAWf.

The system further comprises an intermediate frequency circuit IF coupled to the first mixer and comprising a bulk acoustic wave filter BAW tuned on a frequency substantially equal

with the intermediate frequency BAWf. the system includes a second mixer M2 receiving a signal provided by the intermediate frequency circuit IF and a second frequency synthesizer L02 generating a signal having a frequency substantially equal with the first intermediate frequency BAWf. The calibrating system further includes a level detecting circuit LD coupled to the intermediate frequency circuit IF for determining an amplitude of the intermediate frequency signal. The label R or C attached to the switch S terminals indicate the mode of operation i. e. receiving and calibrating, respectively. A tuning control processor TC is coupled to the first synthesizer LO1 and to the second synthesizer L02 for controlling the frequencies generated by said synthesizers LO1, LO2. The level detecting circuit LD is coupled to the intermediate frequency circuit IF for determining an amplitude of the intermediate frequency signal and provides a signal indicative for said amplitude to the tuning control processor TC. A register Reg is coupled to the tuning control processor TC for memorizing a number corresponding to the intermediate frequency BAWf, the number being used as a correction factor for the first and second synthesizers LO1, L02 in the receiving mode R.

The intermediate frequency circuit IF is coupled to the second frequency synthesizer L02 in the calibrating mode C, the second frequency synthesizer L02 working in a sweeping mode for determining the intermediate frequency BAWf, a binary number corresponding to the intermediate frequency BAWf being memorized in the register Reg. the first and the second frequency synthesizers provide signals whose frequency is controlled by digital signals provided by the tuning control processor TC. The tuning control processor may be embedded in the same chip with the receiver or may be an external processor.

Furthermore, it may be interfaced with the receiver via an adequate interface protocol as e. g.

I2C. It is mentioned that the intermediate frequency circuit has a band-pass characteristic centered on the intermediate frequency and therefore when an input signal has a frequency substantially equal with the intermediate frequency the signal provided by the intermediate frequency circuit has a maximum amplitude value. Hence, it behaves as a maximum detector in calibrating mode. During calibration the frequency of the second synthesizer is swept step- wise from a minimum value to a maximum value e. g. from 1100 MHz till 1300 MHz if the intermediate frequency is 1200 MHz. Recall that the frequency is binary controlled. With increasing frequency the output level of the intermediate frequency signal increases, so that at each step of the tuning control processor TC controlling the second synthesizer L02 the register receives a clock pulse. When the maximum has been passed, the pulses are negative

and the register does not receives any clock pulse. With this algorithm the frequency with maximum transfer of the BAW filter is stored.

After calibration the receiver is switched in the receiving mode. The calibration may take place at the beginning of a receiving session or anytime when this is necessary for preventing the errors that may appear determined by aging and/or climatic factors as temperature and humidity.

Fig. 2 depicts a block schematic of a calibrating system according to a second embodiment of the invention. In this embodiment the receiver is slightly modified and comprises a frequency divider D coupled to an input of the receiver and to the first synthesizer L01 via respective switches S'. The frequency divider provides a divided signal fOl having a frequency that in n-th part of the frequency of the signal generated by the first synthesizer fL01. The divided signal fOl and the signal generated by the first synthesizer are mixed in the first mixer Ml. The Register Reg provides a binary number being indicative for the first intermediate frequency BAWf.

In Fig. 2, common blocks with blocks in Fig. 1 have same letters. After the first mixer Ml, the signal has a frequency that equals (n-1)/n of the first synthesizer LO 1 frequency and this frequency has to be in the intermediate frequency band BAWf. For example, if the frequency generated by the first synthesizer is 1700 MHz and the intermediate frequency is 1200 MHz it results that n should be 3.

Fig. 3 depicts a more detailed description of a level detection circuit according to the invention. The intermediate frequency circuit IF has a band-pass transfer characteristic centered on the intermediate frequency BAWf and therefore when an input signal has a frequency substantially equal with the intermediate frequency BAWf the signal provided by the intermediate frequency circuit IF has a maximum amplitude value. The level detecting circuit LD comprises a level detector 1 coupled to a differentiation circuit 2 followed by a slicer 3. The level detector 1 is coupled to an automatic gain control amplifier included in the intermediate frequency circuit IF as shown in Fig. 4.

The output level of the intermediate frequency circuit IF is detected by the level detector 1 that may be a part of the intermediate frequency circuit IF, the level detector LD being coupled to an automatic gain control amplifier AGC. The frequency for which the AGC is set for the smallest gain, is stored in the register.

It is remarked that the scope of protection of the invention is not restricted to the embodiments described herein. Neither is the scope of protection of the invention restricted by the reference signs in the claims. The word'comprising'does not exclude other parts than those mentioned in the claims. The word'a (n)' preceding an element does not exclude a plurality of those elements. Means forming part of the invention may both be implemented in the form of dedicated hardware or in the form of a programmed purpose processor. The invention resides in each new feature or combination of features.