Dual frequency receiver radio frequency front end circuit
By employing a frequency synthesizer and a mixer unit with combining functions in the RF front-end circuit of the dual-frequency receiver, the problems of poor chip integration and high cost are solved, and independent automatic gain control and signal-to-noise ratio improvement are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ALLYSTAR TECH (BEIJING) CO LTD
- Filing Date
- 2023-07-18
- Publication Date
- 2026-06-26
AI Technical Summary
Existing dual-frequency receiver RF front-end circuits suffer from poor chip integration, high cost, high circuit complexity, and lack of independent automatic gain control.
A mixer unit with frequency synthesizer and synthesis functions is used to achieve internal image suppression of dual-frequency signals by designing a specific local oscillator signal frequency relationship, and to independently control the automatic gain in each channel.
It reduces circuit cost and complexity, improves chip integration, ensures that automatic gain control of each channel operates independently, and enhances the signal-to-noise ratio.
Smart Images
Figure CN116996084B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of radio frequency technology, and in particular to a radio frequency front-end circuit for a dual-frequency receiver. Background Technology
[0002] Traditional dual-band receiver RF front-end circuits consist of two independent RF channels, each containing an independent low-noise amplifier (LNA), mixer, filter (LPF), variable gain amplifier (PGA), analog-to-digital converter (ADC), and frequency synthesizer (PLL). Thus, the cost of circuitry for receiving dual-band signals is twice that of a single-band receiver. Figure 1 As shown.
[0003] Some improvements, such as the "single-chip dual-frequency global satellite navigation receiver" disclosed in patent CN201010620937.0, are as follows: Figure 2 Patent CN201010620937.0 contains two independent radio frequency channels, and... Figure 1 In comparison, patent CN201010620937.0 can be configured with two receiving modes: the first is a low-IF / zero-IF receiving mode, because the signals of receiving channel A and receiving channel B are mirror images of each other, so when receiving channel A is turned on, the signal of receiving channel B will be suppressed, realizing single-frequency reception; the second is a superheterodyne receiving mode, where the dual-frequency signals enter the two receiving channels 41 and 42 respectively. At this time, the off-chip filter LC BPF 406 / 425 is turned on, and the two frequency synthesizers are a radio frequency synthesizer (1.1GHz-1.6GHz) and an intermediate frequency synthesizer (150MHz-220MHz), which can reduce the mutual interference between the two frequency synthesizers. However, the use of an off-chip intermediate frequency filter is not conducive to chip integration and increases costs.
[0004] Patent CN201010206235.8 proposes "a dual-system dual-frequency navigation receiver radio frequency front-end device", such as Figure 3 Similar to patent CN201010620937.0, it also uses a double downconversion technology. The first downconversion produces a high-frequency signal of 110MHz-220MHz, which needs to be filtered by four external filters to suppress image signals, which is also not conducive to chip integration.
[0005] The practice disclosed in patent CN201510404289.8 is as follows Figure 4This invention makes good use of the characteristic that different frequency bands are mirror images of each other, and achieves image suppression without the use of an external intermediate frequency filter, using only the internal circuit of the chip. It only requires one frequency synthesizer and cleverly designs the frequency generated by the frequency synthesizer to achieve dual-frequency reception. However, this invention has three problems: First, module 40 is a filter with signal synthesis function. This filter is more difficult to design than a general filter, and requires more components and a larger area, which increases the design complexity and circuit cost. Second, in order to receive GNSS navigation satellite signals of 1150MHz-1510MHz, module 10 is a broadband low-noise amplifier. While receiving signals, it will also receive more interference signals, reducing the circuit signal-to-noise ratio. Third, radio frequency receivers are generally designed with automatic gain control (AGC) circuits so that when the input energy changes, the AGC can adjust the overall gain of the radio frequency receiver to ensure that the analog-to-digital converter (ADC) outputs relatively stable energy for baseband processing. However, in patent CN201510404289.8, channel one and channel two share a broadband low-noise amplifier. When there is interference frequency in one channel, the AGC will adjust the gain of both channel one and channel two at the same time, so that the signal-to-noise ratio of the other receiving channel cannot be maximized.
[0006] The practices disclosed in patents CN201010620937.0 and CN201010206235.8 require the use of off-chip intermediate frequency filters, which is not conducive to chip integration and has a high cost.
[0007] The approach disclosed in patent CN201510404289.8 is difficult to design for the synthesis function filter, the broadband LNA will capture more interference energy, and the approach of sharing an LNA is not conducive to the receiver's automatic gain control. Summary of the Invention
[0008] The technical problem to be solved by the embodiments of the present invention is to provide a dual-frequency receiver RF front-end circuit, so as to reduce design cost and circuit cost, and enable the automatic gain control of each channel to operate independently.
[0009] To address the aforementioned technical problems, this invention provides a dual-frequency receiver RF front-end circuit, comprising a first RF receiving channel and a second RF receiving channel, and a frequency synthesizer. Both the first and second RF receiving channels are composed of a low-noise amplifier, a mixer unit, a complex bandpass filter, an adjustable gain amplifier, and an analog-to-digital converter connected sequentially. Each mixer unit includes a first mixer, a second mixer, a third mixer, and a fourth mixer. The first and second mixers are connected in series, as are the third and fourth mixers. The first and third mixers receive signals from the low-noise amplifier, and the output signals from the second and fourth mixers are superimposed on the complex bandpass filter.
[0010] Furthermore, the frequency synthesizer outputs first local oscillator signals LO1_I and LO1_Q, and second local oscillator signals LO2_I and LO2_Q. LO1_I and LO1_Q have the same frequency but a 90-degree phase difference; LO2_I and LO2_Q have the same frequency but a 90-degree phase difference. The first and third mixers of the first RF receiving channel receive the first local oscillator signals LO1_Q and LO1_I, and the second and fourth mixers of the first RF receiving channel receive the second local oscillator signals LO2_Q and LO2_I. The first and third mixers of the second RF receiving channel receive the first local oscillator signals LO1_Q and LO1_I, and the second and fourth mixers of the second RF receiving channel receive the second local oscillator signals LO2_I and LO2_Q.
[0011] Furthermore, the angular frequency w1 of the first local oscillator signal satisfies:
[0012] w1=(w A +w B ) / 2;
[0013] Where w A and w B These are the angular frequencies of the signals entering the first and second radio frequency receiving channels, respectively.
[0014] The angular frequency w2 of the second local oscillator signal satisfies:
[0015] w2 = w1 / N;
[0016] N is greater than or equal to 1.
[0017] The beneficial effects of this invention are as follows:
[0018] 1. This invention uses only one frequency synthesizer to achieve dual-frequency signal reception; and the area and power consumption of the LNA can be made very small under current technological conditions, so the circuit cost of two LNAs does not increase much.
[0019] 2. This invention does not utilize an external intermediate frequency filter; instead, it achieves image suppression within the chip.
[0020] 3. This invention does not use complex signal synthesis filters, thus reducing design costs and circuit complexity;
[0021] 4. The automatic gain control of each channel in this invention can operate independently. Attached Figure Description
[0022] Figure 1 This is a schematic diagram of the radio frequency front-end circuit of a traditional dual-frequency receiver.
[0023] Figure 2This is a structural schematic diagram of patent CN201010620937.0.
[0024] Figure 3 This is a structural schematic diagram of patent CN201010206235.8.
[0025] Figure 4 This is a structural schematic diagram of patent CN201510404289.8.
[0026] Figure 5 This is a schematic diagram of the structure of the radio frequency front-end circuit of the dual-frequency receiver according to an embodiment of the present invention.
[0027] Explanation of icon numbers
[0028] The first RF receiving channel includes a low-noise amplifier 10, a mixer unit 20, a complex bandpass filter 30, an adjustable gain amplifier 40, and an analog-to-digital converter 50; the second RF receiving channel includes a low-noise amplifier 11, a mixer unit 21, a complex bandpass filter 31, an adjustable gain amplifier 41, and an analog-to-digital converter 51. Detailed Implementation
[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0030] In this embodiment of the invention, directional indicators (such as up, down, left, right, front, back, etc.) are only used to explain the relative positional relationship and movement of each component in a specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.
[0031] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.
[0032] Please refer to Figure 5 The dual-frequency receiver radio frequency front-end circuit of this invention includes a frequency synthesizer, a first radio frequency receiving channel, and a second radio frequency receiving channel.
[0033] like Figure 5The first radio frequency receiving channel consists of a low noise amplifier 10 (LNA), a mixer unit 20 (MIXER), a complex bandpass filter 30 (CBPF), an adjustable gain amplifier 40 (PGA), and an analog-to-digital converter 50 (ADC) connected in sequence. The second radio frequency receiving channel consists of a low noise amplifier 11 (LNA), a mixer unit 21 (MIXER), a complex bandpass filter 31 (CBPF), an adjustable gain amplifier 41 (PGA), and an analog-to-digital converter 51 (ADC) connected in sequence.
[0034] Each mixer unit includes a first mixer, a second mixer, a third mixer, and a fourth mixer, such as... Figure 5 The first and second mixers in the first row are connected in series, and the third and fourth mixers in the second row are connected in series. The first and third mixers receive signals from the low-noise amplifier, and the output low-IF / zero-IF signals from the second and fourth mixers are superimposed on the complex bandpass filter.
[0035] This invention achieves the reception of the desired signal and the suppression of the mirror signal through a mixer unit with synthesis function.
[0036] The frequency synthesizer outputs the first local oscillator signals LO1_I and LO1_Q, and the second local oscillator signals LO2_I and LO2_Q. LO1_I and LO1_Q have the same frequency but a 90-degree phase difference; LO2_I and LO2_Q have the same frequency but a 90-degree phase difference.
[0037] The first and third mixers of the first RF receiving channel receive the first local oscillator signals LO1_Q and LO1_I, and the second and fourth mixers of the first RF receiving channel receive the second local oscillator signals LO2_Q and LO2_I; the first and third mixers of the second RF receiving channel receive the first local oscillator signals LO1_Q and LO1_I, and the second and fourth mixers of the second RF receiving channel receive the second local oscillator signals LO2_I and LO2_Q.
[0038] As one implementation method, the angular frequency w1 of the first local oscillator signal satisfies:
[0039] w1=(w A +w B ) / 2;
[0040] Where w A and w B These are the angular frequencies of the signals entering the first radio frequency receiving channel and the second radio frequency receiving channel (hereinafter referred to as frequency one signal and frequency two signal), respectively.
[0041] The angular frequency w2 of the second local oscillator signal satisfies:
[0042] w2 = w1 / N;
[0043] N is greater than or equal to 1. That is, the first local oscillator frequency is N times the second local oscillator frequency, N is greater than or equal to 1, and N is not limited to being an integer or a decimal.
[0044] This invention employs a frequency synthesizer to achieve dual-frequency reception by selecting the frequencies of the first local oscillator and the second local oscillator.
[0045] The working principle of the dual-frequency receiver RF front-end circuit in this embodiment of the invention is as follows:
[0046] 1. A dual-frequency signal w mirrored by the LO1 frequency. A and w B Simultaneously, signals enter the first radio frequency receiving channel (referred to as Channel 1) and the second radio frequency receiving channel (referred to as Channel 2). Assume the frequency of the first signal is w. A The frequency of the two signals is lower than the frequency w. B , where w A and w B These are the angular frequencies of the first and second frequency signals, respectively. Assume the dual-frequency input signal is expressed as A = cos(ω). A t)+cos(w B t).
[0047] 2. Channel 1 LNA 10 amplifies the frequency 1 signal and reduces the noise contribution of the subsequent modules at frequency 1. The frequency 2 signal, as a mirror signal, will also be amplified, but the amplification degree is not as great as that of frequency 1. Channel 2 LNA 11 amplifies the frequency 2 signal and reduces the noise contribution of the subsequent modules at frequency 2. The frequency 1 signal, as a mirror signal, will also be amplified, but the amplification degree is not as great as that of frequency 2.
[0048] 3. The amplified dual-frequency signals from both Channel 1 and Channel 2 enter a mixer unit with synthesis function.
[0049] 4. The principle of the mixer unit is as follows:
[0050] a) The first local oscillator signals LO1_I and LO1_Q can be represented by cos(w1t) and sin(w1t) respectively, and the second local oscillator signals LO2_I and LO2_Q can be represented by cos(w2t) and sin(w2t) respectively, where w1 and w2 are the angular frequencies of the first and second local oscillators, respectively. The frequency of the first local oscillator can be roughly set in the middle of the frequencies of the dual-frequency signals, and the frequency of the second local oscillator can be set to w1 / N, so that the frequency of the first frequency signal is approximately equal to w1 - w1 / N, and the frequency of the second frequency signal is approximately equal to w1 + w1 / N (for example, assuming the first frequency signal is 1.2GHz and the second frequency signal is 1.6GHz, then LO1 can be set around 1.4GHz, and LO2 can be set to satisfy LO1 + w1 / N). LO2 is around 1.6GHz, so LO1–LO2 will be around 1.2GHz. Different LO1 and LO2 values may be chosen depending on the design, but as long as this condition is met, it's acceptable. w1 and w2 represent the frequency; w1 can be set near the middle of the dual-band signal.
[0051] b) The signal obtained after the dual-frequency signal of channel one undergoes two frequency conversions can be expressed as: A*cos(w1t)*cos(w2t)+A*sin(w1t)*sin(w2t)=A*cos(w1t-w2t)=A*cos((w1-w1 / N)t)= (cos(w1t-w2t)) A t)+cos(w B t))*cos((w1-w1 / N)t)=(cos((w A -w1+w1 / N)t)+cos((w A +w1-w1 / N)t)+ cos((w B -w1+w1 / N)t)+cos((w B +w1-w1 / N)t)) / 2;
[0052] c) The signal obtained after the dual-frequency signal of channel two undergoes a second frequency conversion can be expressed as: A*cos(w1t)*sin(w2t)+A*sin(w1t)*cos(w2t)=A*sin(w1t+w2t)=A*sin((w1+w1 / N)t)= (cos(w1t+w2t)) A t)+cos(w B t))*cos((w1+w1 / N)t)=(cos((w A -w1-w1 / N)t)+cos((w A +w1+w1 / N)t)+ cos((w B -w1-w1 / N)t)+cos((w B +w1+w1 / N)t)) / 2;
[0053] d) Since the input signal A contains a lower frequency signal (frequency one) and a higher frequency signal (frequency two), the frequency of the first frequency signal is w. A It's right around the frequency (w1-w1 / N), where the frequency of the second signal is w. B At frequency (w1+w1 / N), after two down-conversions and signal synthesis, the frequency one signal of channel one falls near the zero frequency in the low-intermediate frequency range, as shown in the first item of step b, while the second, third, and fourth items are located in the higher intermediate frequency range. The frequency two signal of channel two will fall near the zero frequency in the low-intermediate frequency range, as shown in the third item of step c, while the first, second, and fourth items are all located in the higher intermediate frequency range. In this way, dual-frequency signals can be received simultaneously using only one frequency synthesizer, and only one signal located in the low-intermediate frequency range is received in each channel. The other frequency items are located in the higher intermediate frequency range and can be filtered out by the subsequent filter.
[0054] 5. After down-conversion, the signal passes through a complex bandpass filter. This serves two purposes: first, it filters out unwanted high-frequency signals and retains the required low-frequency signals; second, it filters out sideband energy that is opposite to the signal frequency, thereby improving the overall signal-to-noise ratio of the receiver.
[0055] 6. The two-channel variable gain amplifier and analog-to-digital converter complete the signal amplification and analog-to-digital conversion functions, and send the signal to the digital baseband for further signal processing, thus realizing the function of the entire RF front-end circuit.
[0056] The mixer unit of this invention operates in current mode, which can simply realize the function of current summation without the need for a combining filter, thus simplifying the design complexity. The chip of this invention implements image rejection internally, eliminating the need for an external LC bandpass filter, thereby improving chip integration and reducing circuit cost. The narrowband LNA of this invention reduces the received interference energy and improves the circuit signal-to-noise ratio. The two independently operating channels of this invention allow the system AGC to independently control the gain of each RF channel, resulting in a more rational system structure.
[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A dual-frequency receiver radio frequency front-end circuit, comprising a first radio frequency receiving channel and a second radio frequency receiving channel, characterized in that, It also includes a frequency synthesizer. The first and second radio frequency receiving channels are each composed of a low-noise amplifier, a mixer unit, a complex bandpass filter, an adjustable gain amplifier, and an analog-to-digital converter connected in sequence. Each mixer unit includes a first mixer, a second mixer, a third mixer, and a fourth mixer. The first and second mixers are connected in series, and the third and fourth mixers are connected in series. The first and third mixers receive the signal from the low-noise amplifier, and the output signals of the second and fourth mixers are superimposed on the complex bandpass filter. The frequency synthesizer outputs first local oscillator signals LO1_I and LO1_Q, and second local oscillator signals LO2_I and LO2_Q. LO1_I and LO1_Q have the same frequency but a 90-degree phase difference; LO2_I and LO2_Q have the same frequency but a 90-degree phase difference. The first and third mixers of the first RF receiving channel receive the first local oscillator signals LO1_Q and LO1_I, and the second and fourth mixers of the first RF receiving channel receive the second local oscillator signals LO2_Q and LO2_I. The first and third mixers of the second RF receiving channel receive the first local oscillator signals LO1_Q and LO1_I, and the second and fourth mixers of the second RF receiving channel receive the second local oscillator signals LO2_I and LO2_Q. The angular frequency w1 of the first local oscillator signal satisfies: w1=(w A +in B ) / 2; Where w A and w B These are the angular frequencies of the signals entering the first and second radio frequency receiving channels, respectively. The angular frequency w2 of the second local oscillator signal satisfies: w2 = w1 / N; N is greater than or equal to 1.