KR19990038102A - Digital automatic gain control circuit - Google Patents

Abstract

The present invention relates to a digital automatic gain control circuit for converting a received signal into a digital signal and automatically controlling the gain of the received signal using the converted digital signal to obtain a more constant and stable output signal. The received signal is attenuated by a voltage controlled attenuator. The attenuated signal is mixed with the local oscillation frequency, demodulated into baseband signals of I and Q, and then converted into a digital baseband signal. The converted I. Q digital baseband signal is used as an address in the program ROM to draw a control voltage for digital automatic gain control, convert the extracted digital automatic gain control voltage into an analog signal, and then perform low pass filtering. The resultant voltage is applied to the voltage control attenuator as a control voltage for automatic gain control to obtain a more stable and constant received signal.

Description

Digital automatic gain control circuit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital automatic gain control circuit. In particular, a digital automatic gain is obtained by converting a received signal into a digital signal and automatically controlling the gain of the received signal using the converted digital signal. It relates to a control circuit.

In general, an automatic gain control circuit is a circuit that automatically controls the gain so that the output remains substantially constant even if the level of the input signal changes in the wireless receiver or amplifier.

A conventional analog automatic gain control circuit for performing such a function is shown in FIG. 1.

As shown therein, a first amplifier 1 for amplifying an input analog wireless signal to a predetermined level, a signal amplified by the first amplifier 1 and a local oscillation frequency generated by the local oscillator 2 are mixed. A mixer (3) for outputting an intermediate frequency, a second amplifier (4) for amplifying the intermediate frequency output from the mixer (3) to a predetermined level, and an intermediate frequency output from the second amplifier (4). A first band filter section 5 for filtering into a band, a voltage control attenuator 6 for attenuating a signal output from the first band filter section 5 by a voltage output from a phase equalizer, and the voltage control Third and fourth amplifiers 7 and 8 for sequentially amplifying the analog signal output from the attenuator 6 and a second band filter unit for filtering the analog signal output from the fourth amplifier 8 to a predetermined band. (9), in the second band filter section (9) A fifth amplifier 10 for amplifying the output analog signal to a predetermined level and outputting the received analog signal; a signal strength detector 11 detecting the strength of the analog signal output from the fifth amplifier 10; A loop filter 12 for converting an AC component of a signal output from the intensity detector 11 into a DC component, a DC component output from the loop filter 12, and a signal output from the fifth amplifier 10. It consists of a phase equalizer 13 which outputs an automatic gain control voltage so as to maintain its linearity and transmits it to the voltage controlled attenuator 6.

Referring to the operation of the conventional analog automatic gain control circuit configured as described above is as follows.

First, the received analog radio signal is amplified to a predetermined level by the first amplifier 1, and the mixing unit 3 is output from the analog radio signal amplified by the first amplifier 1 and the local oscillator 2 The intermediate frequency is extracted by mixing the reference local oscillation frequency.

The intermediate frequency thus extracted is once again amplified to a predetermined level by the second amplifier 4 and filtered by the first band filter section 5 to the set band.

The voltage control attenuator 6 attenuates the signal filtered by the first band filter unit 5 with the control voltage initially set by the phase equalizer 13, and the attenuated analog received signals are converted into the third and fourth signals. It is sequentially amplified by the amplifiers 7 and 8 and transferred to the second band filter section 9.

The second band filter unit 9 filters the transmitted analog received signal to a predetermined band, and the filtered received signal is amplified to a predetermined level in the fifth amplifier 10 and then output as a received signal.

The signal strength detector 11 detects the strength of the signal output from the fifth amplifier 10, and the loop filter 12 performs the AC component (high frequency) of the analog signal detected by the signal strength detector 11. Component) into a direct current component.

The analog signal of the DC component thus converted is input to the phase equalizer 13, and the phase equalizer 13 linearly changes the input signal strength and the change ratio of the DC component output from the loop filter unit 12. The control voltage for gain control is outputted to the voltage control attenuator 6 so as to be maintained.

The voltage controlled attenuator 6 then controls the gain by controlling the attenuation of the signal output from the first band filter section 5 with the control voltage.

However, the conventional analog automatic gain control circuit as described above requires a complicated detection circuit, an integrator, and a linear circuit for linearly changing the output of the integrator in order to detect an analog signal. There was a problem.

In addition, since the automatic gain control by the analog signal, it also acted as a factor to reduce the call quality.

Accordingly, the present invention has been proposed to solve all the problems of the conventional analog gain control circuit as described above.

An object of the present invention is to provide a digital automatic gain control circuit which converts a received signal into a digital signal and automatically controls the gain of the received signal using the converted digital signal to obtain a more constant and stable output signal. .

The present invention for achieving the above object,

Voltage control attenuation means for attenuating the input intermediate frequency signal according to the control voltage and dividing the attenuated signal into I and Q signals and outputting them;

Demodulating means for mixing the I, Q signals outputted from the voltage controlled attenuation means and the local oscillation frequency, demodulating them into baseband signals, and amplifying the signals to a predetermined level;

Analog / digital conversion means for converting the I and Q baseband signals demodulated by the demodulation means into digital baseband signals, respectively;

A programmable ROM for outputting data for automatic gain control in accordance with the digital baseband signal obtained from the analog / digital converting means;

Digital / analog conversion means for converting automatic gain control data generated in the programmable ROM into an analog signal corresponding thereto;

And a low pass filtering means for low pass filtering the analog automatic gain control signal output from the digital / analog converting means and transferring the result as an automatic gain control voltage to the voltage control attenuation means.

In the above, the demodulation means comprises: a first mixer for mixing the analog Q signal obtained from the voltage controlled attenuation means with the local frequency output from the local oscillator; A phase shifter for shifting the phase of the local oscillation frequency output from the local oscillator by 90 degrees; A second mixer for mixing the 90 ° phase shifted local oscillation frequency obtained by the phase shifter and the I signal obtained by the voltage controlled attenuation means; And first and second amplifiers for amplifying the baseband signals obtained by the first and second mixers, respectively, to a predetermined level.

The analog / digital converting means may further include: a first analog / digital converter for converting the baseband I signal obtained from the demodulation means into a corresponding digital signal; And a second analog-to-digital converter for converting the baseband Q signal obtained from the demodulation means into a digital signal corresponding thereto.

The low pass filtering means includes: a first low pass filter for low pass filtering the analog baseband signal obtained from the digital / analog conversion means; A second low pass filter for low pass filtering the inverted signal of the analog baseband signal obtained by the digital / analog conversion means; And an operational amplifier which amplifies the voltage difference of the signals obtained from the first and second low pass filters to a predetermined level and transfers the result to the voltage control attenuation means as a control voltage for automatic gain control.

In addition, the technical means for achieving the object of the present invention,

And a latch means for transmitting the digital I and Q signals output from the analog / digital converting means to the channel card, respectively.

Hereinafter, described in detail with reference to the accompanying drawings the operation of the preferred embodiment of the present invention.

1 is a conventional analog automatic gain control circuit diagram,

2 is a block diagram of a digital automatic gain control circuit according to the present invention;

3 is a detailed configuration diagram of the low pass filter of FIG.

<Explanation of symbols for main parts of the drawings>

20: voltage control attenuator 30: demodulator

40: Analog-to-digital converter 50: Programmable ROM

60: Digital / analog conversion part 70: Low pass filter part

80: latch 90: channel card

2 is a block diagram of a digital automatic gain control circuit according to the present invention.

Here, reference numeral 20 denotes a voltage control attenuator for attenuating the input intermediate frequency signal according to the control voltage and dividing the attenuated signal into I and Q signals. The reference numeral 30 denotes the voltage control attenuation unit 20. A demodulator for mixing the I, Q signals and the local oscillation frequency, respectively, and demodulating the baseband signal and amplifying the signal to a predetermined level.

Further, reference numeral 40 denotes an analog / digital converter for converting the demodulated I and Q baseband signals into digital baseband signals, respectively, and reference numeral 50 denotes the analog / digital converter 40. Programmable ROM outputs data for automatic gain control according to the digital baseband signal obtained by the reference numeral 60 denotes a digital / analog for converting automatic gain control data generated in the programmable ROM 50 into a corresponding analog signal. It is a conversion unit.

In addition, reference numeral 70 denotes a low pass filter for low pass filtering the analog automatic gain control signal output from the digital / analog converter 60 and transmitting the result as an automatic gain control voltage to the voltage control attenuation unit 20. Reference numeral 80 denotes a latch unit for latching the digital baseband signal obtained from the analog / digital converting unit 40 and transmitting the latched digital baseband signal to the channel card 90.

In the above, the demodulator 30 includes: a first mixer 32 for mixing the analog Q signal obtained from the voltage controlled attenuator 20 with the local frequency output from the local oscillator 31; A phase shifter 33 for shifting the phase of the local oscillation frequency output from the local oscillator 31 by 90 degrees; A second mixer (34) for mixing the 90 ° phase shifted local oscillation frequency obtained from the phase shifter (33) and the I signal obtained from the voltage controlled attenuation section (20); And first and second amplifiers 35 and 36 which amplify the baseband signals respectively obtained by the first and second mixers 32 and 34 to a predetermined level.

In addition, the analog-to-digital converter 40 may include a first analog-to-digital converter 41 for converting the baseband I signal obtained from the demodulator 30 into a corresponding digital signal, and the demodulator 30. And a second analog-to-digital converter 42 for converting the baseband Q signal obtained at &lt; RTI ID = 0.0 &gt;

The low pass filter 70 may include: a first low pass filter 71 for low-pass filtering an analog baseband signal obtained by the digital / analog converter 60; A second low pass filter 72 for low-pass filtering an inverted signal of the analog baseband signal obtained by the digital / analog converter 60; Computation of amplifying the difference voltage of the signals obtained by the first and second low pass filters 71 and 72 to a predetermined level and transferring the result to the voltage control attenuation unit 20 as a control voltage for automatic gain control. It consists of an amplifier 73.

In FIG. 3, reference numerals R1 to R5 are resistors, and C1 and C2 are capacitors.

The operation of the digital automatic gain control circuit according to the present invention configured as described above is as follows.

First, when the intermediate frequency IF of the received analog radio signal is input to the voltage controlled attenuator 20, the voltage controlled attenuator 20 is a control voltage for automatic gain control obtained from the low pass filter unit 70. The intermediate frequency is attenuated, and separated into analog I and Q signals and transmitted to the demodulator 30 at the rear stage.

The demodulator 30 outputs the Q baseband signal by mixing the analog Q signal obtained from the voltage controlled attenuator 20 and the local oscillation frequency obtained from the local oscillator 31 with the first mixer 32. The second mixer 34 outputs an output signal of the phase shifter 33 for shifting the phase of the local oscillation frequency output from the local oscillator 31 by 90 ° and an analog I signal output from the voltage control attenuation unit 20. Is mixed to output the baseband I signal.

The output I and Q baseband signals are respectively amplified and demodulated in the first and second amplifiers 35 and 36 and transmitted to the analog / digital converter 40 at the rear stage.

The analog-to-digital converter 40 peak-to-peak analog I and Q signals obtained from the demodulator 30 to the first and second analog-to-digital converters 41 and 42, respectively, around -0.5V. Peak To Peak is sampled to 1V and converted into a digital signal. That is, the analog-to-digital converter 40 is 8-bit digital data (I signal 4 bits, Q that sampled the amplitude of the analog signal 4 bits according to a predetermined clock frequency (sampling frequency) of the analog signal varying from 0 to -1) Signal 4 bits) to the latch unit 80 and the programmable ROM 50, respectively.

Then, the latch unit 80 latches the 8-bit I and Q baseband signals obtained from the analog / digital converter 40 to transmit them to the channel card 90, and the programmable ROM 50 transmits the analog. According to the 8-bit baseband signal output from the / digital converter 40, digital data for automatic gain control as shown in the following table (1-1) is output.

I input signal Q input signal Programmable ROM Output 0000 0000 11000110 0001 0001 10111110 0010 0010 10101110 0011 0011 10010110 0100 0100 01110110 0101 0101 01001110 0110 0110 00011110 0111 0111 00000000 1000 1000 00000000 1001 1001 00011110 1010 1010 01001110 1011 1011 01110110 1100 1100 10010110 1101 1101 10101110 1110 1110 10111110 1111 1111 11000110

Meanwhile, as described above, the digital data for 8-bit automatic gain control output from the programmable ROM 50 is converted into an analog signal corresponding to the digital / analog converter 60, and the digital / analog converter ( 60 transmits the converted control voltage for the automatic gain control and the control voltage whose phase of the control voltage is inverted to the low pass filter unit 70.

The low pass filter 70 low-pass filters, amplifies, and amplifies the analog automatic gain control voltage and the phase inverted analog control voltage respectively obtained by the digital / analog converter 60 to output the result.

That is, as shown in FIG. 3, the low pass filter 70 converts the analog control voltage obtained from the digital / analog converter 60 into the first low pass filter 71 including the resistor R3 and the capacitor C1. The low-pass filtering is performed, and the inverted analog control voltage is low-pass filtered by the second low pass filter 72 including the resistor R4 and the capacitor C2.

The low-pass filtered control voltages are respectively input to the non-inverting terminal (+) and the inverting terminal (-) of the operational amplifier 73, and the operational amplifier 73 is input to the two terminals (+ and-), respectively. The voltage difference voltage is amplified to a predetermined level, and the result is transferred to the voltage control attenuation unit 20 as a control voltage so that the gain of the received signal is controlled.

As described above, the present invention has the effect of simplifying the configuration of the automatic gain control circuit since the control voltage for automatic gain control is extracted using the digital signal.

In addition, the digital automatic gain control circuit has fewer components compared to the analog automatic gain control circuit, thereby reducing the overall component number, thereby reducing the cost in circuit construction.

Claims (5)

In the automatic gain control circuit for automatically controlling the gain of the received radio signal, Voltage control attenuation means for attenuating the input intermediate frequency signal according to the control voltage and separating the attenuated signal into I and Q signals and outputting the separated signal; Demodulating means for mixing the I, Q signals outputted from the voltage controlled attenuation means and the local oscillation frequency, demodulating them into baseband signals, and amplifying the signals to a predetermined level; Analog / digital conversion means for converting the I and Q baseband signals demodulated by the demodulation means into digital baseband signals, respectively; A programmable ROM for outputting data for automatic gain control in accordance with the digital baseband signal obtained from the analog / digital converting means; Digital / analog conversion means for converting automatic gain control data generated in the programmable ROM into an analog signal corresponding thereto; And a low pass filtering means for low pass filtering the analog automatic gain control signal output from the digital / analog converting means and transmitting the result as an automatic gain control voltage to the voltage control attenuation means. 2. The apparatus of claim 1, wherein the demodulation means comprises: a first mixer for mixing an analog Q signal obtained from the voltage controlled attenuation means with a local frequency output from a local oscillator; A phase shifter for shifting the phase of the local oscillation frequency output from the local oscillator by 90 degrees; A second mixer for mixing the 90 ° phase shifted local oscillation frequency obtained by the phase shifter and the I signal obtained by the voltage controlled attenuation means; And a first and a second amplifier for amplifying the baseband signals respectively obtained by the first and second mixers to a predetermined level, respectively. 2. The apparatus of claim 1, wherein the analog / digital converting means comprises: a first analog / digital converter for converting a baseband I signal obtained from the demodulation means into a corresponding digital signal; And a second analog-to-digital converter for converting the baseband Q signal obtained from the demodulation means into a digital signal corresponding thereto. 2. The apparatus of claim 1, wherein the low pass filtering means comprises: a first low pass filter for low pass filtering an analog baseband signal obtained from the digital / analog conversion means; A second low pass filter for low pass filtering the inverted signal of the analog baseband signal obtained by the digital / analog conversion means; And an operational amplifier configured to amplify the difference voltage of the signals obtained from the first and second low pass filters to a predetermined level, and to transmit the result to the voltage control attenuation means as a control voltage for automatic gain control. Gain control circuit. The digital automatic gain control circuit according to claim 1, further comprising latching means for latching digital I and Q signals output from the analog / digital converting means and transferring the digital I and Q signals to the channel card.