The study of oscillators has never stopped. From the early vacuum tube era when the late transistor era, both theoretical and circuit structure and performance, both volume and production costs have undoubtedly made a leap forward, but in a long period of time are in the stage of assembling with separate components, its performance is poor, the cost is relatively high, the volume is large and difficult to mass production. As the communications field continues to move forward, the end product more and more demanding light, thin, short, small, more and more demanding low-cost, high-performance, high-volume production, which will no longer be able to separate the components of the previous combination of modes, and put forward new requirements and challenges. The development of integrated circuit technology to meet these requirements, in particular, the mainstream CMOS process to provide solutions to the above requirements, the development of monolithic integrated oscillator has made great progress.
However, due to process constraints, RF circuits are mostly designed using GaAs, Bipolar, and BiCMOS processes, which are difficult to integrate with the mainstream standard CMOS processes. Therefore, the design of standard CMOS VCOs with superior performance has become a hot topic in RF circuit design in recent years.
In recent years, with the rapid development of the field of communication electronics, the requirements for electronic equipment are increasingly high, especially for such basic components as oscillators and so on. But over the years, China's research investment in this area, whether in the military or civilian are not enough attention, limited to the introduction and improvement of the state, has not reached a qualitative leap, no independent intellectual property rights (IP), but also the reason why the electronic communication class lagged behind the developed countries is an important reason. And most of our country is still utilizing the traditional bipolar process, resulting in products in the volume, weight, cost are larger, a variety of parameter performance is not superior, poor stability, difficult to integrate with the modern mainstream CMOS process and so on is the development of China's related areas of bottlenecks.
China's market potential in the field of electronic communications is very large, independent research on high-performance, high-quality, low-cost voltage-controlled oscillator market prospects, great significance.
1.2 The main performance indicators of VCO
The performance indicators of VCO[4] mainly include: frequency tuning range, output power, (long-term and short-term) frequency stability, phase noise, spectral purity, ESC speed, push frequency coefficients, frequency traction and so on.
Frequency tuning range is one of the main indicators of a VCO, and is related to the topology of the resonator and the circuit. Usually, the larger the tuning range, the smaller the resonator's Q. The Q of the resonator is related to the phase noise of the oscillator, and the smaller the Q, the worse the phase noise performance.
The frequency stability of an oscillator includes long-term stability and short-term stability, each of which includes amplitude stability and phase stability, respectively. Long-term phase stability and short-term amplitude stability are usually not considered in oscillators; long-term amplitude stability is mainly affected by the ambient temperature, and short-term phase stability mainly refers to phase noise. Phase noise is a major limiting factor in a variety of high-performance, wide dynamic range frequency conversion. In digital communication systems, the phase noise of the carrier signal also affects the carrier tracking accuracy.
Other indicators, the spectral purity of the oscillator indicates the ability to suppress harmonics and clutter in the output; the push factor indicates the change in oscillation frequency due to changes in the supply voltage; the frequency traction indicates the effect of changes in the load on the oscillation frequency; and the speed of the electric tuning indicates the ability of the oscillation frequency to change quickly or slowly with the tuning voltage.
In the voltage-controlled oscillator indicators, frequency tuning range and output power is a measure of the oscillator's primary indicators, the remaining indicators based on the specific application background and focus. For example, as part of the frequency synthesizer, the requirements of the VCO can be summarized in the following aspects: should meet the high phase noise requirements; to have a very fast tuning speed, frequency temperature characteristics and frequency drift performance should be good; power flatness is good; good electromagnetic compatibility.
1.3 Domestic and foreign status
At present, many domestic and foreign manufacturers have produced VCOs for different applications.
Table 1-1 are representative of the domestic thirteen and Agilent produced some of the voltage-controlled oscillator products of some of the indicators:
Table 1-1
Model Frequency range (GHz) FM Voltage (V) Operating Voltage/Current (V/mA) Output Power (dBm) Phase Noise (dBc/Hz)
HE487 3.0~3.7 0~15 12/30 +12 1.5
-90@10KHz
HE488 3.7~4.2 0~15 12/30 +10 1.5
-87@10KHz
VTO-8200 2.0~3.0 2~24 15/50 +10 1.5
-95@50KHz
VTO-8240 2.4~3.7 2~30 15/50 +10 1.5
-95@50KHz
VTO -8360 3.6~4.3 8~24 15/50 +10 1.5
-100@50KHz
The above products are packaged in TO-8 packages. For the circuit within the package is generally used in the transistor core and varactor diode core, which can reduce the pin distribution of inductance, capacitance, reduce the distribution of parameters to consider. However, the production of such packages require specialized equipment, complex production process, high threshold of entry, high product prices. When the frequency is high, the impact of these parameters on circuit performance is very significant. Careful consideration needs to be given to the design to select the appropriate circuit form and minimize the sensitivity of the circuit to the device parameters.
In addition, since the previous also used a ferrite device called YIG (yttrium iron right garnet) ferrite device as a resonator voltage-controlled oscillator, resonance frequency tuned with an external magnetic field, the tuning bandwidth can be very wide, because the YIG resonator can be a very high Q, the YIG oscillator has a very good performance of phase noise. However, due to the higher cost and more difficult to design, the current required is high and the tuning speed is slower than the varactor diode tuned VCO. This design only analyzes and designs the voltage controlled oscillator with varactor diode tuning.