A low-pass filter of the frequency synthesizer

Abstract

The invention relates to a low-pass filter of a frequency synthesizer. The filter includes a first capacitor, a sixth resistor, a sixth capacitor, one end of the first capacitor is used as a circuit input end; the other end is connected with the ground; one end of the sixth resistor is connected with the circuit input end; the other end of the sixth resistor is connected with one end of the sixthcapacitor; the other end of the sixth capacitor is grounded; The circuit is characterized by further comprising a differential amplification circuit, the anode input end of the differential amplification circuit is connected with the other end of the sixth resistor, the cathode input end of the differential amplification circuit is connected with the output end of the sixth resistor, the output end of the differential amplification circuit is further connected with one end of the fifth resistor, and the other end of the fifth resistor is connected with the input end of the circuit. For an application scenario where the LPF is integrated on a chip, the capacitance value of C2 in the LPF is further reduced through the capacitance multiplication technology, the LPF area is reduced, and therefore the chip cost is reduced.

Description

technical field [0001] The invention belongs to the field of wireless communication, in particular to a low-pass filter of a frequency synthesizer. Background technique [0002] With the development of wireless communication technology, the requirements for wireless communication chips are getting higher and higher. On the one hand, the integration of wireless communication chips is required, and on the other hand, higher requirements are placed on the area and power consumption of wireless communication chips, thereby improving the competitive advantage of chips. . [0003] Frequency synthesizer (Frequency synthesizer) is one of the most important applications of phase-locked loop, and it is the core module of wireless communication chip. Such as figure 1 As shown, a radio frequency transceiver usually consists of three main subsystems, namely a receiver, a transmitter, and a frequency synthesizer. The function of the frequency synthesizer is to provide the required loca...

AI Technical Summary

Problems solved by technology

[0008] Due to the limitation of integrated circuit technology, the capacitance density of the capacitor integrated on the chip is not large. Due to the limitation of the loop bandwidth of the frequency synthesizer, the value of the capacitor C2 in the LPF is very large, and the LPF occupies a large part of the area of ​​the frequency synthesizer. Integrated LPF will increase chip area and chip cost

For frequency synthesizers in some special application scenarios, the loop bandwidth value is very low, which leads to a large LPF capacitor area and cannot be integrated on-chip. It is generally realized by off-chip devices, which will bring adverse effects in three aspects. :

[0009] 1) The off-chip device implements LPF, which increases the system application cost;

[0010] 2) To implement LPF with off-chip devices, the chip needs to add two additional packaging pins, which increases packaging cost and complexity;

[0011] 3) The implementation of LPF by off-chip devices increases the complexity of application debugging;

Images