With the continuous advancement of GNSS (Global Navigation Satellite System) and the rapid development of China's Beidou second-generation satellite navigation system, the application of satellite navigation and positioning systems is becoming more widespread and deeply integrated into various industries. As a result, there is growing interest in developing low-power, low-noise, and cost-effective satellite receiver chips. Among these components, the mixer plays a crucial role in RF front-end circuits by enabling frequency conversion. This paper focuses on the design of a low-noise mixer suitable for wideband GNSS applications.
**1. Design Specifications**
The primary objective of this mixer design is to develop a low-noise, wideband mixer that covers all GNSS frequency bands, ranging from 1 GHz to 1.6 GHz. The key specifications include:
- Input RF frequency: 1–1.6 GHz
- IF output frequency: 46 MHz
- RF input power: -120 to -30 dBm
- Local oscillator (LO) power: -10 dBm
- Operating voltage: 3.3 V
- Conversion gain: 10 dB
- Noise figure: 4 dB
- 1 dB compression point: -17 dBm
These parameters ensure the mixer can operate effectively in a wide range of GNSS applications while maintaining high performance and stability.
**2. Mixer Circuit Design**
The circuit design of the mixer is illustrated in Figure 1. The load circuit consists of R1, C1, R2, and C2, forming two first-order RC low-pass filters to suppress unwanted high-frequency signals such as LO and RF leakage at the mixer output.
At the transconductance stage, Q8, R9, Q5, R7, Q6, and R8 form a current mirror configuration. The base resistors R7 and R8 are carefully chosen to ensure proper injection of the RF signal into Q5 and Q6 without causing interference. However, they must not be too large, as this could reduce the base current and affect the operating point, leading to lower gain. Since the input is differential, R7 and R8 must be equal, and Q5 and Q6 should have the same size.
In the switching stage, Q7 is connected as a diode to provide a bias voltage for the switching transistor. Q1 to Q4 are identical transistors, and R5 and R6 are matched to ensure effective injection of the LO signal into the switch. R4 and R3 are used to set the bias current and voltage for the switching stage, respectively. Their values are optimized to maintain stable operation and good linearity.
Capacitors C1 and C2 are both 2 pF, and the bias transistors Q7 and Q8 are selected with smaller sizes to save power. Their models are N05005011SH. The resistor values are listed in Table 1.
**3. Simulation Results**
To evaluate the performance of the mixer, we used the “MixConvGainNF Schematic Template†environment in ADS for simulation. When the RF input frequency was 1.575 GHz, the input power was -85 dBm, and the LO power was -10 dBm, the measured conversion gain was 15.79 dB, and the single-sideband noise figure was 4 dB, as shown in Figure 2.
The mixer was also tested across the entire 1–1.6 GHz frequency range to ensure it meets the requirements of a GNSS receiver. The results show a consistent gain of over 15 dB with less than 2 dB variation across the 600 MHz bandwidth, demonstrating excellent performance and reliability. Additionally, the noise figure remains stable, confirming the design’s ability to deliver low noise over a wide frequency range.
Linearity is another critical factor for mixers, especially in GNSS applications where the RF signal power typically ranges from -110 dBm to -55 dBm. After amplification by a low-noise amplifier, the RF power entering the mixer ranges from -100 dBm to -40 dBm. The simulation results in Figure 4 show that the mixer achieves a 1 dB compression point of -17 dBm, indicating a sufficient linear range for practical use.
**4. Performance Analysis**
Based on the simulation results in Figure 3, the mixer maintains a gain of over 15 dB with less than 2 dB variation across the 1–1.6 GHz band, meeting the design requirements. The noise figure also shows minimal variation, confirming the mixer’s capability to deliver broadband low-noise performance.
Furthermore, the 1 dB compression point of -17 dBm, as shown in Figure 4, ensures that the mixer operates within the required linear range for GNSS applications. These results validate the effectiveness of the design and its suitability for integration into future GNSS receivers.
Neoprene Zipper Cable Sleeve,Neoprene Cable Management Sleeve,Zipper Sleeve Cable Wrap,Neoprene Wire Sleeve
Shenzhen Huiyunhai Tech.Co., Ltd. , https://www.cablesleevefactory.com