Zero-intermediate-frequency receiver and communication equipment

Abstract

The invention discloses a zero intermediate frequency receiver and communication equipment, the zero intermediate frequency receiver comprises an antenna, a low noise amplifier and a power limiting circuit, and the antenna is used for receiving a radio frequency signal; the low-noise amplifier is connected with the antenna and is used for amplifying the radio frequency signal; and the power limiting circuit is connected with the low-noise amplifier and is used for controlling the output power of the low-noise amplifier according to the power of the radio frequency signal, so that the power ofan interference signal in the demodulated signal is smaller than a first preset power. By means of the mode, the output power of the low-noise amplifier can be controlled, so that the power of interference signals in signals output by the demodulation circuit is smaller than the power of bottom noise, and the receiving quality of a receiver is improved.

Description

technical field [0001] The present application relates to the technical field of communication, in particular to a zero-IF receiver and communication equipment. Background technique [0002] The RF part of the zero-IF receiver (ZIF, Zero Intermediate Frequency) only includes a high-frequency low-noise amplifier and a mixer, the gain is not high, it is easy to meet the requirements of linear dynamic range, and there is no image frequency interference; When using the analog channel of the receiver, if the input signal power is large enough, even a continuous signal will produce a noise that is not needed by the user. The energy is only a little bigger than the background noise (background noise), but under the amplification of the audio power amplifier, obvious sounds can be heard in the speaker, which affects the user's use. Under normal circumstances, only "noisy" white noise should be heard the sound of. [0003] When two walkie-talkies communicate at close range, the use...

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Problems solved by technology

[0002] The RF part of the zero-IF receiver (ZIF, Zero Intermediate Frequency) only includes a high-frequency low-noise amplifier and a mixer, the gain is not high, it is easy to meet the requirements of linear dynamic range, and there is no image frequency interference; When using the analog channel of the receiver, if the input signal power is large enough, even a continuous signal will produce a noise that is not needed by the user. The energy is only a little bigger than the background noise (background noise), but under the amplification of the audio power amplifier, obvious sounds can be heard in the speaker, which affects the user's use. Under normal circumstances, only "noisy" white noise should be heard the sound of

[0003] When two walkie-talkies communicate at close range, the user of one of the walkie-talkies just presses Push to Talk (PTT, Push to Talk) and does not speak. It is relatively small, and it can only be heard when the ear is close to the speaker; when the zero-IF walkie-talkie receives an in-band signal, the local oscillator signal of the zero-IF walkie-talkie should theoretically have the same frequency as the in-band signal, but because of the difference in the crystal oscillator frequency of different walkie-talkies, Under normal circumstances, it is impossible to achieve completely the same frequency, and there will always be a frequency difference of tens to hundreds of HZ. After the frequency difference is mixed and demodulated by the mixer, a single frequency twice the difference frequency will be generated. frequency, the single frequency is the noise that people do not want, and the noise cannot be filtered out by the audio filter; the generation of the noise is related to the input equivalent second-order intercept point (IIP2, Second Order Input Intercept Point) of the mixer. The problem is inherent in the development of zero-IF intercoms

[0004] The inventors of the present application have found in the long-term research and development that there are generally two means to solve this problem in the prior art. One is the low-intermediate frequency scheme, which makes the frequency of the local oscillator signal shifted by several KHZ, and the generated noise is doubled. After down-converting, the noise will be far away from the useful signal, and then the noise will be filtered out through the audio filter; however, the bandwidth of the useful signal will increase. The other is that when the input power is greater than -25dBm, the receiving system will automatically switch to the low-IF state. If the input power is less than -25dBm, the receiving system will maintain the zero-IF state. When the input signal is small, this solution will not Affects sensitivity, but when switching, another noise will be generated, which cannot achieve the purpose of eliminating noise

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