KR19990058821A - Receiving circuit and receiving method for wireless subscriber network system terminal - Google Patents

Abstract

The present invention relates to a receiving circuit and a receiving method for a wireless subscriber network system terminal, and more particularly, to a method for automatic gain adjustment of a transceiver for a system terminal in a wireless subscriber network system using a wideband code division multiple access scheme.

The present invention provides a first low noise amplifier for low noise amplifying a high frequency input signal; A high frequency band pass filter connected to the low noise amplifier to increase selectivity of a received signal; A second low noise amplifier connected to the high frequency band pass filter and configured to low noise amplify the filtered signal; A mixer connected to the second low noise amplifier, the mixer downconverting a high frequency signal to an intermediate frequency; An intermediate frequency band pass filter connected to the mixer and configured to remove unwanted waves generated by the mixer with respect to the down-converted intermediate frequency signal and increase selectivity of the receiver; A first automatic gain adjusting circuit connected to the intermediate frequency band pass filter, the first automatic gain adjusting circuit maintaining a constant level of a received signal; A demodulator coupled to the primary automatic gain control circuit for demodulating a received signal into a baseband I / Q signal; A low pass filter connected to the demodulator for selecting a baseband I / Q signal; And a second automatic gain adjustment circuit coupled to the low pass filter, the second automatic gain adjusting circuit maintaining a constant level of a received signal.

As described above, the present invention is configured by dividing the automatic gain control circuit into primary and secondary, so that the weak circuit portion is not overwhelmed and consequently improves performance of adjacent channel selectivity and linearity of the receiver.

Description

Receiving circuit and receiving method for wireless subscriber network system terminal

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving circuit and a receiving method for a wireless local loop (WLL) system terminal, and in particular, uses a broadband code division multiple access (CDMA) scheme. The present invention relates to an automatic gain control (AGC) method of a transceiver for a system terminal in a wireless subscriber network system.

A base station system that provides a communication service to a terminal moving in an arbitrary area typically modulates and demodulates a signal in an intermediate frequency band and a high frequency unit that processes a radio signal. It consists of a digital signal processing unit (Digital Unit) to convert to RF.

The base station and the terminal transceiver for transmitting and receiving wireless signals have a gain adjustment function for adjusting the level of the transmitted and received signals as well as up and down frequency conversion functions for the transmitted and received signals. Conventional receiver circuits are configured in a double super heterodyne scheme or a single super heterodyne scheme.

The heterodyne method is the most basic method used for converting a signal spectrum having a baseband to a higher frequency at a low frequency band. The basic principle of the heterodyne method is to perform modulation using a specific intermediate frequency (IF) rather than the low frequency (RF) or voice signal used in actual wireless communication. Therefore, the heterodyne method has an advantage that the amplification and filtering operations can be performed at a fixed center frequency regardless of the received frequency.

The receiver circuit amplifies the high frequency signal received from the antenna with a low noise amplifier (LNA). The amplified signal is first removed by a band pass filter (BPF) and down-converted to a first intermediate frequency by a mixer. The mixer generates a first intermediate frequency signal by combining a local oscillation frequency signal and an input frequency signal generated from a separate stable local oscillator (LO). The down-converted primary intermediate frequency signal is adjusted by the automatic gain control (AGC) circuit, and then converted into a received baseband signal (I / Q signal) through a demodulator.

The received signal converted into the baseband signal is sent to the digital signal processing unit to perform analog / digital conversion. In some cases, the first intermediate frequency is fed back into the mixer, downconverted to the second intermediate frequency, and then automatically adjusted.

The terminal receiver configured as described above performs automatic gain adjustment only in the primary or secondary intermediate frequency band. The gain adjusted signal is down converted to a baseband signal and then sent to a digital signal processor for analog / digital conversion. However, since the maximum allowable input level of automatic gain control circuits and demodulators is on the low side, automatic gain control circuits must adjust the gain by 60 to 70 dB or more in the very low signal range.

When the gain of the automatic gain control circuit is high, the interference signal introduced into the adjacent channel band is excessively amplified and exceeds the allowable input level range of the demodulator. Therefore, the demodulator is forced to operate in the nonlinear region. When operating in the nonlinear region, the output of the demodulator is not constant. Then, the signal transmission to the digital signal processor is not performed smoothly, and the performance of the receiver is degraded.

For example, assume that the level of the signal received from the base station is low. The automatic gain adjustment circuit then operates at maximum gain to increase the gain of the received signal. However, if there is a device generating an interference signal near the terminal, the interference signal may be introduced very high in the adjacent channel of the reception band of the terminal receiver. In this case, in order to sufficiently remove signals other than the desired reception band, a surface acoustic wave (SAW) filter is usually used.

However, in a system using wideband code division multiple access technology, the SAW filter introduces a large group delay, which degrades the system performance. Therefore, there is a limit to the use of the SAW filter. As a result, when the automatic gain control circuit operates at the maximum gain state without sufficiently removing the interference signal, the demodulator has a problem in that it operates in the nonlinear region by the interference signal.

Therefore, in order to solve the above problems, the present invention divides the gain control function between the intermediate frequency band and the baseband in the receiving circuit of the wireless subscriber network terminal using the wideband code division multiple access technology, thereby selecting adjacent channels. An object of the present invention is to provide a receiving method and apparatus for a wireless subscriber network system terminal having improved linearity and input third order intercept point 3 (IIP3).

1 is a block diagram showing a receiving circuit of a system terminal according to the present invention.

One preferred embodiment of the method according to the invention devised to achieve the object as described above is

Low noise amplifying the high frequency input signal;

Selectively passing only a high frequency band for increasing selectivity of a received signal; Low noise amplifying the selected signal;

Down converting the high frequency signal to an intermediate frequency;

Removing the unwanted wave generated in the mixer for the downconverted intermediate frequency signal;

Adjusting gain to keep the received signal level constant;

Demodulating the received signal into a baseband I / Q signal; Passing only lowpass signals to select only baseband I / Q signals; And

Adjusting gain to maintain a constant received signal level.

In addition, a preferred embodiment of the device according to the present invention for achieving the above object,

A first low noise amplifier (LNA) for low noise amplifying the high frequency input signal;

A high frequency band pass filter (RF BPF) connected to the low noise amplifier to increase selectivity of a received signal;

A second low noise amplifier connected to the high frequency band pass filter and configured to low noise amplify the filtered signal;

A mixer connected to the second low noise amplifier, the mixer downconverting a high frequency signal to an intermediate frequency;

An intermediate frequency band pass filter connected to the mixer and configured to remove unwanted waves generated by the mixer with respect to the down-converted intermediate frequency signal and increase selectivity of the receiver;

A first automatic gain adjusting circuit connected to the intermediate frequency band pass filter, the first automatic gain adjusting circuit maintaining a constant level of a received signal;

A demodulator coupled to the primary automatic gain control circuit for demodulating a received signal into a baseband I / Q signal;

A low pass filter (LPF) connected to the demodulator and configured to select a baseband I / Q signal; And

It is connected to the low pass filter and includes a second automatic gain adjustment circuit that maintains a constant level of the received signal.

In the present invention, it is preferable that the receiving circuit further includes a transmission upconversion circuit in the same board.

The receiving circuit preferably further comprises a phase locked loop (PLL) synthesizer, which is a local oscillator,

Preferably, the first low noise amplifier determines a noise figure and a gain of a receiver.

Preferably, the first and second low noise amplifiers have a high 1 dB compression point.

The mixer is preferably a double balance mixer,

The intermediate frequency band pass filter is preferably a surface acoustic wave (SAW) filter,

In order to overcome the high insertion loss caused by the SAW filter and to maintain a low noise figure, it is preferable to add an intermediate frequency amplifier to the output of the SAW filter,

Preferably, the primary automatic gain adjustment circuit has a gain adjustment value of about 30 dB,

Preferably, the gain of the first automatic gain adjustment circuit is adjustable within the gain range of the entire circuit.

Preferably, the secondary automatic gain adjustment circuit has a gain adjustment value of about 40 dB,

The gain of the secondary automatic gain adjustment circuit is preferably adjustable within the gain range of the entire circuit.

The present invention relates to a receiver circuit of a terminal transceiver used in a wireless subscriber network system using a wideband code division multiple access technology, and converts a signal introduced into an antenna of a terminal into a baseband signal and then converts the signal into a digital signal processor. The present invention relates to a configuration of a receiving circuit up to transmission and an automatic gain adjusting method.

1 is a block diagram showing a receiving circuit of a system terminal according to the present invention. As shown, a low noise amplifier (LNA) for low noise amplification of a high frequency input signal, a high frequency band pass filter (RF BPF) for increasing selectivity of a received signal, and a double balance mixer for downconverting a high frequency signal to an intermediate frequency ( Double Balance Mixer), an intermediate frequency band pass filter (SAW filter) that removes unwanted waves generated by the mixer for down-converted intermediate frequency signals and increases receiver selectivity, and a first-order automatic gain that keeps the received signal level constant. A regulating circuit, a demodulator for demodulating the received signal into baseband I / Q signals, a low pass filter (LPF) for selecting the baseband I / Q signals, and two to keep the received signal level constant. Includes a car automatic gain control circuit. Also included in the same board is a Phase Locked Loop Synthesizer, which is used as a local oscillator for the transmit up-frequency conversion circuit and the transmit / receive circuit.

Referring to Figure 1 with respect to the operation of the receiver configured as described above are as follows.

The high frequency input signal from the high frequency input stage is amplified in a low noise amplifier with a high 1 dB compression point. The amplifier in the first amplifier stage determines the noise figure and gain of the receiver.

To increase the selectivity of the received signal, pass a high-frequency bandpass filter and then amplify the signal level in the second amplifier. The amplified signal is input to a double balanced mixer and downconverted to an intermediate frequency.

The downconverted intermediate frequency signal includes the unwanted wave generated in the downconverting mixer. An intermediate frequency bandpass filter (SAW filter) eliminates unwanted waves from the mixer, increasing receiver selectivity.

To overcome the high insertion loss caused by the SAW filter and to maintain a low noise figure, an intermediate frequency amplifier is used. The signal amplified in the intermediate frequency amplifier is adjusted by a first order automatic gain adjustment circuit with a gain adjustment range of about 30 dB. The gain-adjusted signal is input to a demodulator and converted into a baseband I / Q signal. The converted I / Q signal removes unwanted waves other than the low band I / Q signal by a low pass filter, and then adjusts the gain by about 40 dB by a second automatic gain adjustment circuit.

Through the above process, the overall dynamic range of 70 dB is maintained, and amplified to a predetermined level required for analog / digital conversion in the digital signal processing unit by a final operational amplifier. As a result, the demodulated baseband I / Q signal is output.

The present invention operating as described above,

By dividing the receiver's automatic gain control circuit into primary and secondary circuits, it prevents the weak circuit from becoming excessive and consequently improves the receiver's adjacent channel selectivity, linearity and IIP3.

Claims (13)

Low noise amplifying the high frequency input signal; Selectively passing only a high frequency band for increasing selectivity of a received signal; Low noise amplifying the selected signal; Down converting the high frequency signal to an intermediate frequency; Removing the unwanted wave generated in the mixer for the downconverted intermediate frequency signal; A first automatic gain adjustment step to keep the received signal level constant; Demodulating the received signal into a baseband I / Q signal; Passing only lowpass signals to select only baseband I / Q signals; And And a second automatic gain adjusting step of keeping the received signal level constant. A first low noise amplifier (LNA) for low noise amplifying the high frequency input signal; A high frequency band pass filter (RF BPF) connected to the low noise amplifier to increase selectivity of a received signal; A second low noise amplifier connected to the high frequency band pass filter and configured to low noise amplify the filtered signal; A mixer connected to the second low noise amplifier, the mixer downconverting a high frequency signal to an intermediate frequency; An intermediate frequency band pass filter connected to the mixer and configured to remove unwanted waves generated by the mixer with respect to the down-converted intermediate frequency signal and increase selectivity of the receiver; A first automatic gain adjusting circuit connected to the intermediate frequency band pass filter, the first automatic gain adjusting circuit maintaining a constant level of a received signal; A demodulator coupled to the primary automatic gain control circuit for demodulating a received signal into a baseband I / Q signal; A low pass filter (LPF) connected to the demodulator and configured to select a baseband I / Q signal; And And a secondary automatic gain adjustment circuit coupled to the low pass filter, the secondary automatic gain adjustment circuit maintaining a constant level of a received signal. 3. The receiving circuit of claim 2, wherein the receiving circuit further comprises a transmit upconversion circuit within the same board. 3. The receiving circuit of claim 2, wherein the receiving circuit further comprises a phase locked loop (PLL) synthesizer that is a local oscillator. 3. The receiving circuit of claim 2, wherein the first order low noise amplifier determines a noise figure and a gain of a receiver. 3. The receiving circuit of claim 2, wherein the primary and secondary low noise amplifiers have a high 1 dB compression point. 3. The receiving circuit of claim 2, wherein the mixer is a double balance mixer. 3. The receiving circuit of claim 2, wherein the intermediate frequency band pass filter is a Surface Acoustic Wave (SAW) filter. 3. The receiving circuit of claim 2, wherein an intermediate frequency amplifier is added at the output of the SAW filter to overcome the high insertion loss caused by the SAW filter and maintain a low noise figure. 3. The receiving circuit of claim 2, wherein the primary automatic gain adjustment circuit has a gain adjustment value of about 30 dB. 3. The receiving circuit of claim 2, wherein the gain of the primary automatic gain adjusting circuit is adjustable within the gain range of the entire circuit. 3. The receiving circuit of claim 2, wherein the secondary automatic gain adjustment circuit has a gain adjustment value of about 40 dB. 3. The receiving circuit of claim 2, wherein the gain of the secondary automatic gain adjusting circuit is adjustable within the gain range of the entire circuit.