JP7636855B2 - Receiver - Google Patents

Description

This invention relates to a receiver that extracts a desired audio frequency signal from a received signal and reproduces the audio.

Receivers that play back audio have traditionally been equipped with an automatic gain control circuit (internal AGC) that adjusts the gain and output audio to an appropriate range depending on the received signal level. However, if there is an excessive input to the receiver's antenna input, devices such as the power amplifier section may be damaged or saturated. For this reason, a separate automatic gain control circuit (external AGC) is required to monitor the received power on the input side and attenuate the received signal. In this case, for example, as shown in Figure 2, a possible configuration is to monitor the received power in the digital section and attenuate the received signal in the stage before the digital section.

However, because it has two automatic gain control circuits and exhibits an operation and behavior in which the subsequent internal AGC converges after the previous external AGC converges, it takes time for convergence, resulting in a decrease and deterioration of response performance. In particular, with the above configuration, when the received power increases instantaneously, the signal captured by the RF_ADC (analog/digital converter) saturates and overflows before the external AGC converges, causing the power detection value in the external AGC to be estimated too low, resulting in gradual attenuation of the received signal. As a result, the convergence and response of the subsequent internal AGC slows down, and responsiveness deteriorates.

To solve this problem, a technique is known in which the time constants of the internal AGC and the external AGC are set to different values (see, for example, Patent Document 1). For example, by setting the time constant of the internal AGC large and the time constant of the external AGC small, overshoot and undershoot of the output signal are suppressed.

Japanese Unexamined Patent Publication No. 53-72441

However, the technology in Patent Document 1 only sets the time constants of the internal AGC and the external AGC to different values, which is insufficient to suppress the effect of the external AGC in the previous stage on the internal AGC in the subsequent stage, and this may result in reduced responsiveness.

The present invention aims to provide a receiver that can prevent damage to devices caused by excessive input and has good responsiveness.

In order to solve the above problem, the invention of claim 1 is a receiver comprising: a first automatic gain control circuit that attenuates a gain of a received signal before digital conversion in accordance with a signal level of the digitally converted received signal; a gain correction unit that corrects the gain of the received signal to a value before attenuation by multiplying the attenuated and digitally converted received signal by the reciprocal of the amount of attenuation by the first automatic gain control circuit at a timing to cancel out the attenuation; a channel filter that removes unnecessary frequency components of the corrected received signal; and a second automatic gain control circuit that adjusts the gain of the received signal that has passed through the channel filter within a predetermined range, wherein the gain correction unit cancels out the attenuation by adjusting a delay and multiplying the reciprocal so that the influence of the first automatic gain control circuit is suppressed in the second automatic gain control circuit.

According to the invention of claim 1, since the gain of the received signal is attenuated by the first automatic gain control circuit, it is possible to prevent damage to the device even if there is an excessive input. In addition, since the gain of the received signal attenuated by the first automatic gain control circuit in the preceding stage is corrected to the gain before attenuation by the gain correction unit, the influence of the first automatic gain control circuit in the subsequent stage is suppressed and reduced. Moreover, since the correction is performed at a timing that cancels the attenuation, it is possible to further suppress and reduce the influence of the first automatic gain control circuit. As a result, the convergence time in the second automatic gain control circuit becomes faster independently without depending on the first automatic gain control circuit, and responsiveness is improved.

In addition, the gain correction unit multiplies the attenuated received signal by the inverse of the amount of attenuation by the first automatic gain control circuit, making it possible to correct the attenuation of the received signal. Moreover, since it only requires multiplication by the inverse of the amount of attenuation, it can be configured simply.

According to the invention of claim 2, the delay is adjusted and the reciprocal is multiplied, making it possible to more appropriately cancel out attenuation.

1 is a schematic block diagram showing a receiver according to an embodiment of the present invention; FIG. 1 is a schematic block diagram showing a conventional receiver equipped with an internal AGC and an external AGC.

The present invention will be described below based on the illustrated embodiment.

Figure 1 is a schematic block diagram showing a receiver 1 according to an embodiment of the present invention. This receiver 1 is a device that extracts a desired audio frequency signal from a received signal and reproduces audio, and mainly comprises an A/D conversion unit (RF_ADC) 2, an external AGC (first automatic gain control circuit) 3, a digital down-converter (DDC) 4, an external AGC correction unit (gain correction unit) 5, a channel filter 6, an internal AGC (second automatic gain control circuit) 7, and a demodulation unit 8.

The A/D conversion unit 2 is an analog/digital converter that converts the analog received signal received by the antenna and input into a digital signal.

The external AGC 3 is an automatic gain control circuit that attenuates the gain of the received signal before digital conversion according to the signal level of the received signal digitally converted by the A/D conversion unit 2, and is equipped with an analog variable attenuator 31 arranged upstream of the A/D conversion unit 2. That is, it detects the signal level and strength of the received signal output from the A/D conversion unit 2, and outputs an attenuation amount according to this signal level to the variable attenuator 31. The received signal received by the antenna is then attenuated by this attenuation amount by the variable attenuator 31 and input to the A/D conversion unit 2, thereby preventing the output signal from becoming saturated. Here, the attenuation amount output from the external AGC 3 to the variable attenuator 31 is also output to the external AGC correction unit 5, which will be described later.

The digital downconverter 4 is a converter that reduces the frequency and sampling rate of the received signal output from the A/D conversion unit 2, thereby ensuring processing time in the channel filter 6, etc.

The external AGC correction unit 5 is a circuit unit that corrects the gain of the received signal to the value before attenuation by multiplying the attenuated received signal by the reciprocal of the amount of attenuation by the external AGC 3 at the timing to cancel out the attenuation by the external AGC 3. In other words, it references a correction value that is the reciprocal of the amount of attenuation transmitted from the external AGC 3 from the inverse table 51 in chronological order and transmission order. For example, if the amount of attenuation from the external AGC 3 is -1 dB, it outputs an amplitude correction value of 1.122, which corresponds to +1 dB, from the inverse table 51.

Then, the received signal output from the digital down-converter 4 is sequentially multiplied by the correction value output from the inverse table 51 by the multiplier 53, thereby amplifying the level of the received signal from the digital down-converter 4 and correcting the attenuation. At this time, the correction value is multiplied while delaying by the delay circuit 52 so that the signal is amplified at a timing that cancels out the attenuation caused by the external AGC 3. In other words, the correction value is multiplied so that the timing and signal part attenuated by the external AGC 3 is amplified and corrected while delaying and adjusting only the control delay of the variable attenuator 31 and the signal delay caused by the A/D conversion unit 2 and the digital down-converter 4. In this way, the reciprocal of the attenuation amount is multiplied at a timing that cancels out the attenuation caused by the external AGC 3, thereby returning the gain of the received signal to the state before attenuation.

The channel filter 6 is a filter that removes unnecessary frequency components of the received signal that has been corrected by the external AGC correction unit 5. For example, by configuring it with a filter that has a characteristic in which the gain drops sharply in the high and low frequency bands, unnecessary frequency components are removed from the received signal, leaving only the frequency components necessary for reception.

The internal AGC 7 is an automatic gain control circuit that adjusts the gain of the received signal that has passed through the channel filter 6 to a predetermined range. That is, in order to stabilize the level of the sound reproduced from the speaker (not shown), the output level is increased or decreased according to the signal level from the channel filter 6. Specifically, like a conventional automatic gain control circuit, the signal level and strength of the received signal output from the channel filter 6 is detected, and the level of the received signal from the channel filter 6 is adjusted by an attenuator (multiplier) according to this signal level.

The demodulation unit 8 is a demodulator that demodulates the received signal output from the internal AGC 7 into an audio signal, and the audio signal demodulated by this demodulation unit 8 is output and played from a speaker via a digital/analog converter (not shown) or the like.

With a receiver 1 configured in this way, the gain of the received signal is attenuated by the external AGC 3, making it possible to prevent damage to the device even if there is excessive input. In addition, the level of the received signal attenuated by the external AGC 3 in the previous stage is corrected by the external AGC correction unit 5 to cancel out the attenuation, so that the influence of the external AGC 3 in the subsequent internal AGC 7 is suppressed and reduced. Moreover, by adjusting the timing of the correction, it is possible to further suppress and reduce the influence of the external AGC 3. As a result, the convergence time of the internal AGC 7 becomes faster independently without depending on the external AGC 3, improving responsiveness.

In addition, in the external AGC correction unit 5, the level of the received signal can be corrected by multiplying the received signal attenuated by the external AGC 3 by the inverse of the attenuation amount. Since it only requires multiplication by the inverse of the attenuation amount, it can be configured simply.

Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there are design changes within the scope of the invention that do not deviate from the gist of the invention, they are included in the invention.

1 Receiver 2 A/D conversion section 3 External AGC (first automatic gain control circuit)
4 Digital down converter 5 External AGC correction section (gain correction section)
51 Inverse table 52 Delay circuit 6 Channel filter 7 Internal AGC (second automatic gain control circuit)
8 Demodulation section

Claims (1)

a first automatic gain control circuit for attenuating a gain of a received signal before digital conversion in accordance with a signal level of the digitally converted received signal;
a gain correction unit that corrects the gain of the received signal to a value before attenuation by multiplying the attenuated and digitally converted received signal by the reciprocal of the amount of attenuation by the first automatic gain control circuit at a timing to cancel the attenuation;
a channel filter for removing unnecessary frequency components of the corrected received signal;
a second automatic gain control circuit that adjusts the gain of the received signal that has passed through the channel filter within a predetermined range;
Equipped with
the gain correction unit cancels the attenuation by adjusting a delay and multiplying the reciprocal so that an effect of the first automatic gain control circuit is suppressed in the second automatic gain control circuit;
23. A receiver comprising: