Abstract:
The present invention relates to temperature compensation of a tuner, and more particularly, to a tuner in which Take-Over Point (TOP) is compensated for according to a temperature. The tuner according to the present invention down-converts a Radio Frequency (RF) wireless signal and outputs the converted signal. The tuner compensates for a TOP depending on a temperature and includes: received signal strength detection means for detecting a received signal strength depending on a RF output of the tuner and transmitting the detected strength to a gain control unit; temperature measurement means for measuring an operating temperature of the tuner and transmitting the measured temperature value; a compensation unit for receiving the measured temperature value from the temperature measurement means to compare the received temperature value with a reference TOP value, compensating for the TOP value depending on variation in temperature and outputting the compensated value; and a gain control unit for receiving the compensated value from the compensation unit to controls the RF output based on the TOP value and the received signal strength received from the received signal strength detection means.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to temperature compensation of a tuner, and more particularly, to a tuner in which Take-Over Point (TOP) is compensated for according to a temperature.  
         [0003]     2. Background of the Related Art  
         [0004]      FIG. 1  shows the construction of a tuner according to the related art.  
         [0005]     FIG. Shows a tuner (receiver)  1  according to the related art.  
         [0006]     After a received signal passes through an antenna  2 , a bandpass filter  3  located at the front end of a first (variable) amplification stage  4  selects a desired frequency band (e.g., WCDMA/GSM, etc.).  
         [0007]     The bandpass filter  3  can be a part of a dual filter shape such as duplexer mode including a transmission-side bandpass filter.  
         [0008]     A mixer  5  down-converts the filtered signal into a zero Intermediate Frequency (IF) by using an orthogonal local oscillator signal ( 6 ) (whose phase is shifted by 90 degrees), which is tuned by a RX synthesizer  7  of a carrier frequency of a received channel.  
         [0009]     The down-converted signal is adapted to bandpass filters  8 ,  10  and a filter  9 . In a digital communication system, this information is converted into digital form by an A/D converter  11  and is then digitally filtered ( 12 ).  
         [0010]     Channel decoding ( 13 ) and other digital functions necessary to recover received information are performed after the operation by the A/D converter ( 11 ).  
         [0011]     A gain control function is an important function in that a range of an input signal is extended such that it can be used in all kinds of tuners. A signal of a Received Signal Strength Indicator (RSSI) block  14  is supplied to a gain control logic block  15  that maintains a received signal to a desired level by controlling the gains of the amplifiers  4 ,  8  and  10 .  
         [0012]     In the conventional tuner, however, a Radio Frequency (RF) gain can be kept constant by the gain control unit and the RSSI. A TOP in which a RF gain falls depending on variation in temperature outside the tuner is varied. Due to this, a problem arises because a signal to noise (S/N) ratio is not kept constant.  
       SUMMARY OF THE INVENTION  
       [0013]     Accordingly, the present invention has been made in view of the above problems occurring in the prior art, and it is an object of the present invention to provide a tuner in which influence depending on variation in temperature can be minimized by changing TOP according to a temperature.  
         [0014]     To achieve the above object, according to the present invention, there is provided a tuner that down-converts a RF wireless signal and outputs the converted signal, wherein the tuner compensates for a TOP depending on a temperature and includes: received signal strength detection means for detecting a received signal strength depending on a RF output of the tuner and transmitting the detected strength to a gain control unit; temperature measurement means for measuring an operating temperature of the tuner and transmitting the measured temperature value; a compensation unit for receiving the measured temperature value from the temperature measurement means to compare the received temperature value with a reference TOP value, compensating for the TOP value depending on variation in temperature and outputting the compensated value; and a gain control unit for receiving the compensated value from the compensation unit to controls the RF output based on the TOP value and the received signal strength received from the received signal strength detection means.  
         [0015]     The reference TOP value may be a value when normal temperature is a reference, and may be a value at about 25° C.  
         [0016]     A measurement range of the temperature measurement means may be set to be in the range of −50° C. to 100° C.  
         [0017]     The tuner may further include an analog-to-digital (A/D) converter that converts an analog value measured by the temperature measurement means into a digital value. In the A/D converter, control bit values may be set as 5-bit depending on a temperature.  
         [0018]     The tuner may further include an A/D converter that converts an analog value measured by the temperature measurement means into a digital value. In the A/D converter, control bit values may be set as 5-bit depending on a temperature. A measurement range of the temperature measurement means may be set to be in the range of −50° C. to 100° C.  
         [0019]     Furthermore, the reference TOP value may have a constant TOP value at a first reference temperature falling within a predetermined range from a normal temperature, which is measured by the temperature measurement means and is used as a reference, a TOP value compensated for by a value, which is increased by a predetermined value from the reference TOP value below the lowest value of the first reference temperature, and a TOP value compensated for by a value, which is decreased by a predetermined value from the reference TOP value below the highest value of the first reference temperature.  
         [0020]     The first reference temperature may be set to be within a range of −15° C. to 50° C. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0022]      FIG. 1  shows the construction of a tuner according to the related art;  
         [0023]      FIG. 2  is a block diagram of a tuner for compensating for TOP according to a temperature according to an embodiment of the present invention;  
         [0024]      FIG. 3  shows a RF gain curve according to the present invention;  
         [0025]      FIG. 4  is a graph for illustrating the relation between TOP and SNR depending on variation in gain;  
         [0026]      FIG. 5  shows a TOP conversion procedure according to the present invention; and  
         [0027]      FIG. 6  shows a characteristic curve of a temperature sensor according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     The present invention will now be described in detail in connection with preferred embodiments with reference to the accompanying drawings.  
         [0029]      FIG. 2  is a block diagram of a tuner for compensating for TOP according to a temperature according to an embodiment of the present invention.  
         [0030]     As shown in  FIG. 2 , the tuner  200  includes a receive unit  210  and a gain compensation unit  220 .  
         [0031]     The receive unit  210  includes a Low Noise Amplifier (LNA)  211 , a Programmable Gain Amplifier (PGA)  212 , an Image-Rejection Mixer (IRM)  213 , a Low Pass Filter (LPF)  214  and an Intermediate Frequency Variable Gain Amplifier (IF VGA)  215 .  
         [0032]     The gain compensation unit  220  includes a gain controller  221 , a compensation unit  222 , a temperature sensor  223  and a RSSI  224 .  
         [0033]     The LNA  211  of the receive unit  210  functions to amplify a received signal while decrease noise signal included in the received signal. The PGA  212  of the receive unit  210  amplifies the signal with improved linearity within a predetermined range, which has been amplified by the LNA  201 .  
         [0034]     The IRM  213  rejects parasitic frequency from the signal, which has been amplified by the LNA  211  and the PGA  212  by filtering an image frequency so that the signal can be subjected to image-rejection down-conversion. The IRM  213  separates a RF stage and an IF stage and can secure stability of the receive unit  210 .  
         [0035]     The LPF  214  of the receive unit  210  allows a specific low pass frequency band to pass through it. The filtered signal is again amplified by the IF VGA  215 .  
         [0036]     In this case, since a weak received signal cannot be sufficiently amplified to become a desired signal only by the LNA  211  of the receive unit  210 , the IF VGA  215  for fine power control is used to amplify a signal with a predetermined gain.  
         [0037]     The gain control unit  221  of the gain compensation unit  220  outputs a control signal in order to compensate for respective gains of the LNA  211 , the PGA  212  and the IRM  213 .  
         [0038]     The compensation unit  222  of the gain compensation unit  220  compensates for a TOP value depending on a temperature based on an initial TOP value and a temperature, which is measured by the temperature sensor  223 , and transmits the compensated TOP value to the gain controller  221 .  
         [0039]     The temperature sensor  223  of the gain compensation unit  220  can be a sensor that can sense a temperature up to +100° C. on the basis of −50° C.  
         [0040]     The RSSI  224  of the gain compensation unit  220  measures a strength of a signal output from the LPF  214  of the receive unit.  
         [0041]     In the tuner  200 , a gain of each of the LNA  211 , the PGA  212  and the IRM  213  of the RF stage is changed depending on a temperature. A TOP is changed depending on variation in gain. As the TOP is varied, the SNR is changed.  
         [0042]     As a result, a constant SNR can be obtained by compensating for a TOP in consideration of a gain value that is varied depending on a temperature.  
         [0043]     A TOP value, which will be compensated for in the compensation unit  222 , is generated based on the initial TOP value and a temperature detected by the temperature sensor  223  and is then applied to the gain control unit  221 .  
         [0044]     The gain control unit  221  sends a control signal to the LNA  211 , the PGA  212  and the IRM  213  of the RF stage so that a value of an output signal of the LPF  214  can be kept constant on the basis of the strength of the signal measured by the RSSI  224  and the TOP value compensated for by the compensation unit  222 .  
         [0045]     If the TOP value is compensated for as described above, a SNR can be kept constant. This will be described in detail with reference to  FIGS. 3 and 4 .  
         [0046]      FIG. 3  shows a RF gain curve according to the present invention.  
         [0047]     The RF gain curve shown in  FIG. 3  indicates a RF AGC value with respect to RF input as a graph.  
         [0048]     A gain from a point “a” to a point “b” indicates a gain part in the PGA having a gain value that is varied depending on a temperature. This part is a part whose TOP value varied depending on a temperature should be compensated for. Points “c”, “d”, “e” and “f” are parts whose gain is compensated for by correcting a gain of the LNA  211  or the IRM  213 .  
         [0049]     A gain value of initial Rfin is amplified to have the highest value of RF AGC[8:0] having a 9-bit control value up to −78 dBm.  
         [0050]     If an input value is lower than TOP value −78 dBm, RFAGC[8:0] has the highest value. If the input value becomes high, the SNR is increased as much as the input value is increased.  
         [0051]     If the input value becomes higher than TOP value −78 dBm, the RF gain is reduced while RFAGC[8:0] is reduced. The SNR has a constant value while the signal is increased.  
         [0052]     TOP compensation depending on variation in temperature according to the present invention is a part from the point “a” to the point “b”. The relation between the TOP and the SNR depending on variation in temperature in a part from the point “a” to the point “b” will be described below with reference to  FIG. 4 .  
         [0053]      FIG. 4  is a graph for illustrating the relation between TOP and SNR depending on variation in gain.  FIG. 4   a  shows the relation between the TOP and the SNR before TOP compensation and  FIG. 4   b  shows the relation between the TOP and the SNR after TOP compensation.  
         [0054]     In addition, in the graph of  FIGS. 4   a  and  4   b , solid line indicates the relation between the TOP and the SNR in a standard temperature, chain dashed line indicates the relation between the TOP and the SNR when a temperature falls from the standard temperature, and chain double-dashed line indicates the relation between the TOP and the SNR when a temperature rises from the standard temperature.  
         [0055]     As shown in  FIG. 4   a , in the case where there is no TOP compensation, if a temperature falls (chain dashed line), a RF gain rises (A→A′). A value of an output signal keeps constant by the RF RSSI  224  and the gain control unit  221 . Therefore, a falling point of the RF gain is decided at TOP′ and the SNR value is lowered accordingly.  
         [0056]     On the other hand, as shown in  FIG. 4   b , in the case where there is TOP compensation, if a temperature falls (chain dashed line), the RF gain rises (A→A′). Although a value of an output signal is kept constant by the RF RSSI  224  and the gain control unit  221 , TOP′ has to be compensated for as much as TOP. Therefore, while the RF gain maintains the same value as the gain value before TOP compensation, the falling point of the RF gain is decided to have the same point as that of the standard temperature. The SNR value becomes the same as that in the standard temperature. The SNR value can be kept constant.  
         [0057]     A case where a temperature rises (chain double-dashed line) is the same as a case where the temperature falls.  
         [0058]     For example, in a tuner or device in which the highest gain of RF is 48 dB and the TOP is −78 dBm at 25° C., if the temperature falls to −40° C., the gain is increased by 10 dB compared with a normal temperature 48 dB, resulting in 58 dB. Therefore, a value of the LPF output, i.e., the input of RF RSSI is increased by 10 dB and RFAGC[8:0] of the tuner is reduced at −78 dBm. The TOP is changed to −88 dBm.  
         [0059]     Therefore, the SNR is increased up to the TOP value. Since the TOP is reduced by 10 dB, a problem arises because the SNR is also reduced by 10 dB.  
         [0060]     That is, in the case of a device whose TOP is changed from −78 dBm at 25° C. to −88 dBm at −40° C., if the TOP value is kept to −78 dBm by compensating for the TOP value by −10 dB, the SNR has a constant value. Therefore, even if the temperature and the input are changed, the output is constant.  
         [0061]     In this case, −10 dB is controlled using a TOP control value. Decision of the control value will be described below in detail with reference to  FIG. 5 .  
         [0062]      FIG. 5  shows a TOP conversion procedure according to the present invention.  
         [0063]      FIG. 5  shows a TOP compensation Take-over point Offset (TOPOFS)[3:0] conversion value depending on a temperature TMP[4:0]. There is shown variation in a TOPOFS value depending on an operating temperature TMP[4:0] value of a device.  
         [0064]     Terms used in the graph shown in  FIG. 5  and the following Equation can be defined as follows.  
         [0065]     TMP (Temperature)[4:0] indicates a digital value of a temperature. Since 5-bit is used, TMP has a total of 32 states.  
         [0066]     TOPI2C (Take-over point Inter IC bus) indicates a TOP value that is initially set.  
         [0067]     TOPOFS (Take-over point Offset)[3:0] indicates a 4-bit value of a TOP that should be compensated for according to TMP.  
         [0068]     RMTMP (Room Temperature)[4:0] indicates a 5-bit value of TMP[4:0] at normal temperature.  
         [0069]     TOPHST (Take-over point Hysteresis)[4:0] indicates a difference in the 5-bit value of the TMP[4:0] when the TOP falls and rises.  
         [0070]     TOPCH (Take-over point Change)[4:0] indicates a difference between RMTMP in which the TOP falls and the 5-bit value of TMP[4:0].  
         [0071]     TOP compensation control depending on variation in temperature according to the present invention can be performed as follows.  
         [0072]     A gain generated in the region ranging from the point “c” to the point “f” shown in  FIG. 3  is compensated for through control of other compensation circuit. This can be expressed in the following Equation 1. 
 
TOP=TOPI2C  (1)
 
 where TOPI2C can be adjusted manually. 
 
         [0073]     In the region ranging from the point “a” to the point “b” shown in  FIG. 3 , the sum of the TOPI2C value that is initially set and the TOPOFS value, i.e., the compensation value of the TOP value depending on variation in temperature is derived. This can be expressed in the following Equation 2. 
 
 TOP=TOPI 2 C+TOPOFS   (2)
 
 where 0≦TOPI2C≧b. 
 
         [0074]     That is, the lowest value TOPmin of TOPOFS is “0” and the highest value TOPmax of TOPOFS is “b”.  
         [0075]     As a result, in the region of the points “c”, “d”, “e” and “f” shown in  FIG. 3 , the TOP has the same value as a TOPI2C value and the gain of TOPI2C is manually controlled. If the TOPI2C value is “0” or higher or “b” or less, however, TOP is the sum of the TOPI2C and TOPOFS values. The lowest value TOPmin of TOPOFS becomes “0” and the highest value TOPmax thereof becomes “b”.  
         [0076]     TOP correction of a device temperature in accordance with the present invention can be expressed in the following table.  
                                                                                           TABLE 1                                       RF Gain (dB)   TOP (dBm)   TOP            Item   Before TOP   After TOP   Before TOP   After TOP   Before TOP   After TOP       ° C.   correction   correction   correction   correction   correction   correction                    −40   58   58   −88   −79   5   8       25   48   48   −78   −78   5   5       85   38   38   −68   −77   5   2                  
 
         [0077]     Table 1 shows a transition of variation in RF gain (dB), TOP (dBm) and TOP depending on a temperature and TOP correction.  
         [0078]     That is, if an ambient temperature of a device is −40° C. before TOP correction, TOP (dBm) is −88 dBm. However, TOP (dBm) is −79 dBm after TOP correction.  
         [0079]     In addition, if an ambient temperature of a device is 85° C. before TOP correction, TOP (dBm) is −68 dBm. However, TOP (dBm) is −77 dBm after TOP correction.  
         [0080]     However, in the case of normal temperature of 25° C., there is no correction. Therefore, TOP (dBm) before and after correction is the same, i.e., −78 dBm.  
         [0081]     In this case, assuming that the TOP value before correction is 5 when a temperature is 5-bit and 32 state, the TOP has a constant value before correction. If there is TOP correction depending on variation in temperature, however, the TOP is 5 at −40° C., 5 at 25° C. and 2 at 85° C.  
         [0082]     A case where a temperature falls will be described with reference to FIGS.  4 ( a ),  4 ( b ) and  5 . In the case where a temperature falls, the gain rises and the SNR falls. In this case, if a TOP value is compensated for by a control signal for TOP compensation (TOP-&gt;TOP′ in  FIG. 4  and 88 dBm-&gt;−79 dBm in  FIG. 5 ), the SNR value is kept to a value at normal temperature, as shown in  FIG. 4 ( b ). That is, during the process in which a temperature of a device is changed to change the gain, and the gain is changed to change the TOP, if TOP that is changed according to a temperature is compensated for, the TOP value can be kept constant. As a result, it is possible to keep the SNR constant.  
         [0083]      FIG. 6  shows a characteristic curve of a temperature sensor according to the present invention.  
         [0084]     In  FIG. 6 , digital output values of the temperature sensor for control, which is related to TOP compensation depending on a temperature, are shows as a curve.  FIG. 6  shows control bit values depending on operating temperatures of the device from −50° C. to 100° C.  
         [0085]     That is, a temperature from −50° C. to 100° C. is divided into 5-bit 32-state(TMP[4:0]) step by step. Each control bit value has resolution of 5° C. per 1-state.  
         [0086]     In this case, the temperature is divided into [00000] to [11111] according to binary number.  
         [0087]     An operation relating to temperature compensation is performed based on the digital values output from the temperature sensor.  
         [0088]     The present invention can realize a tuner with less influence depending on variation in temperature by changing a TOP according to an operating temperature of the tuner.  
         [0089]     While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.