A 180 ghz differential colpitts vco in 65 nm cmos is presented. Colpitts oscillator is another type of oscillator design used to produce an oscillation at a certain frequency. The open loop gain will be set by the gm of the device, by rp and the capacitive divider. Negative resistance osc, differential osc, and vcos. Oscillation in a circuit is undesirable if the circuit is an amplifier or part of a control system which needs to be stable without oscillation. Colpitts oscillator a typical colpitts oscillator and its equivalent circuit is shown in fig. He specifically looked at a colpitts oscillator with automatic gain control. Bjt differential pair osc a bjt version of the oscillator has limited voltage swing determined by the differential pair nonlinearity. The main part of the voltage controlled oscillator is the ring oscillator. To analyze the open loop gain, lets open the loop l rp c. It was observed that the oscillator circuit generates antiphase dual output chaotic carrier and this circuit. Also, the differential complementary colpitts oscillator 300 couples the source nodes n1 and n2 by using the source coupling inductor ls.
Combination of inductor and capacitors determine frequency of oscillator. The circuit is realized by stacking one pmos common drain colpitts oscillator on top on a nmos common drain colpitts oscillators. This enables the colpitts oscillator to operate in lowpower consumption. Frequency tuning is achieved by the onchip varactor and coupling capacitance. The choice and placement of the varactors are analyzed with the y parameters looking into the oscillation loop. Voltage controlled oscillators are electronic circuits designed to produce a periodic sinusoidal signal whose frequency is dependent on the voltage applied at the input 1. Based on this analysis, the varactors are placed close to the source terminal of the transistors to minimize their load effect on the oscillator. A noiseshifting differential colpitts vco roberto aparicio, student member, ieee, and ali hajimiri, member, ieee abstract a novel noiseshifting differential colpitts vco is presented. Another oscillator topology that can be widely used for highfrequency applications and particularly in the application of bipolar oscillators, is the colpitts oscillator see figure 1b. A negative resistance cell is added to the circuit to get a high q value.
To evaluate the design, a conventional crosscoupled differential lc vco, a conventional differential colpitts vco and the proposed vco are simulated using 1. Parallel feedback oscillator topology the feedback arrangement shown in figure 3b is the standard feedback oscillator topology using parallel elements. A bandwidthenhanced differential lcvoltage controlled. Hey guys, ive been asked to design a colpitts oscillator in a common collector configuration using a single bjt.
Cmos implementation of voltage controlled oscillator. Originally, r4 wasnt part of the simulation i added it after i built the circuit and measured the frequency on the scope. The proposed topology increases the negative resistant and enhances the startup difficulty of the conventional colpitts oscillator. Because of high frequencies, small inductance can be used for the radio frequency of oscillation. We can increase the voltage swing by emitter degeneration. A kband differential colpitts crosscoupled vco in 0. The colpitts configuration can be recognized by its use of a tapped capacitor divider c 1 and c 2 in figure 1. Hartley oscillator from wikipedia, the free encyclopedia the hartley oscillator is an electronic oscillator circuit in which the oscillation frequency is determined by a tuned circuit consisting of capacitors and inductors, that is, an lc oscillator. Positive feedback amplifiers oscillators lc and crystal. A new complementary colpitts structure was adopted in a 0. The differential oscillator may also be adapted to form a voltage controlled oscillator. Aug 21, 2015 a colpitts oscillator consists of two capacitive reactances and one inductive reactance in the tank circuit or feedback network.
Take note that the oscillator is a nonlinear circuit, initially. Originally, r4 wasnt part of the simulation i added it after i built the. Colpitts family if we remove the explicit ground connection on the oscillator, we have the template for a generic oscillator. In lab you will have a chance to consider both a sinusoidal oscillator the socalled colpitts oscillator, named after its inventor and a relaxationtype oscillator. Oscillators circuit ideas for designers schematic no. A colpitts oscillator is a discrete lc oscillator that uses a pair of tapped capacitors and an inductor to produce regenerative feedback. The frequency of oscillation is determined by the resonator as in the previous examples. Inser ted in b is the large signal equivalent circuit of a differential pair from chap.
Tuned oscillator is a circuit that generates a radio frequency output by using lc tuned resonant circuit. The colpitts oscillator is a particularly good circuit for producing fairly low distortion sine wave signals in the rf range, 30khz to 30mhz. The differential complementary colpitts oscillator 300 in fig. A more popular alternative is to provide feedback capacitors. A novel complementary colpitts differential cmos vco with low. Moreover, the differential and balanced structure helps limit evenorder harmonics and degrades the common mode noise effects in output. Theoretically the grounded base configuration can be rotated to be the colpitts circuit. The design of differential bipolar chaotic colpitts oscillator was presented in 21. The main difference between colpitts differential oscillator 1100 and colpitts differential oscillator is that in the oscillator 1100, the transistors 1114 and 1116 are added to combine the current sources 1014 and 1016 into one current source 1140. Receiver with colpitts differential oscillator, colpitts. Vco circuit suitable for low phase noise oscillation at the sub1v sup ply voltage.
Circuit model for colpitts a typical fully differential colpitts oscillator is shown in fig. Figure 1 shows a typical colpitts oscillator with a tank circuit in which an inductor l is connected in parallel to the serial combination of capacitors c 1 and c 2 shown by the red enclosure. In this tutorial, we are going to explain colpitts oscillator circuit, basics in brief. Wideband voltage controlled oscillator vco for rf applications. A differential complementary colpitts oscillator based on. Lc oscillator, where the source inductor is sized to pro vide high impedance at two times the oscillation. However, oscillation is desirable in many applications such as sinusoidal signal generator, carrier signal generation is broadcast transmission radio and tv, clock signal in digital systems, etc. An optimized grounded base oscillator design for vhfuhf.
To design and develop hartley, colpitts and differential. Vcc 12v frequency has to be 4k hz vout 3v now i know that the formula for frequency is. The differential amplifier is used in this project for noise immunity since the double ended configuration removes the common mode noise. Physical processes of phase noise differential lc oscillators. The colpitts oscillator is a singletransistor implementation of a sinusoidal oscillator which is widely used in electronic devices and communication systems. The tank inductors engaged in the oscillator are each designed with a quality factor of 9. In our previous articles, we explain about oscillator circuit and hartley oscillator in detail. Lecture 25 negative resistance view, oscillator circuits. It uses current switching to lower phase noise by cyclostationary noise alignment and improve the startup condition. A differential oscillator based on a first colpitts oscillator and a mirror image colpitts oscillator that is coupled to the first colpitts oscillator. The oscillation amplitude is an important parameter for low phase.
Colpitts oscillator was invented by american scientist edwin colpitts in 1918. The circuit was invented in 1915 by american engineer ralph hartley. A study of phase noise in colpitts and lctank cmos oscillators. The circuit of colpitts oscillator is similar to that of hartley oscillator except the difference that rather than making tapped connection at the inductor junctions, it is made at the capacitor junction. The circuit is realized by stacking one pmos common drain colpitts oscillator on top on a nmos common drain colpitts. Us7420429b2 source coupled differential complementary. A kband differential colpitts voltagecontrolled oscillator vco is designed and implemented in a 0.
Im really new to this so help is greatly appreciated. Oscillator is an amplifier with the positive feedback and it converts dc input signal into ac output waveform with certain variable frequency drive and certain shape of output waveform like sine wave or square wave, etc by using the positive feedback instead of input signal. Common collector colpitts oscillator all about circuits. In this paper, we consider the colpitts oscillator as a typical t 4 lc sinusoidal oscillator. I built a transistor based colpitts oscillator and ive been confused by the difference between the standard formulas and circuit behaviour both real and simulated. A source coupled differential cmos complementary colpitts.
This topology is exactly the same as the circuit analyzed by huang except the location of the ground node has been moved to the source. What causes the wave to become triangular and how can i make it more sinelike. Tunedinput and tunedoutput oscillator tunedoutput tunedinput feedback coupling ci rf output c 2 c 1 l 1 2 c co c l 2 1 2 0 2 1 1 l c f s. A colpitts oscillator consists of two capacitive reactances and one inductive reactance in the tank circuit or feedback network. A differential common drain colpitts vco circuit suitable. The colpitts oscillator does not appear to be an inherently better topology than the differential pair oscillator.
A new enhanced differential cmos colpitts oscillator request pdf. Simplified circuit schematic of a differential bipolar colpitts oscillator. A differential complementary colpitts oscillator based on common drain topology mehdi azadmehr, igor paprotny, yngvar berg abstractin this paper we present a new topology complementary differential colpitts oscillator. A comprehensive analysis of phase noise in bipolar colpitts oscillator as well as its comparison with classb oscillator is conducted in. Niknejad university of california, berkeley eecs 142 lecture 22 p. The colpitts oscillator can be realized using valves, transistors, fets or opamp.
This ring oscillator consists of an odd number of invertors which increases the delay and decreases the frequency. R represents total resistance in collector circuit, i. A comparison between the differential colpitts and the lctank oscillator is also carried out, which shows that the latter is capable of a 2db lower phasenoise figureofmerit fom when. Vcc 12v frequency has to be 4k hz vout 3v now i know that the formula for frequency is fo 12pisqrtlct and. Colpitts oscillator basic schematic emphasizing feedback emphasizing loop gain assumptions. It is another type of sinusoidal lc oscillator and is basically a harmonic oscillator, which has a lot of applications. Design of a differential chaotic colpitts oscillator. This statement is often found in the literature, see kotzebue and parrish5. May 25, 2019 colpitts oscillator is a type of lc oscillator which falls under the category of harmonic oscillator and was invented by edwin colpitts in 1918. The designed circuit topology consists of two singleended colpitts lctank vcos, and the differential vco is obtained by using a crosscoupled nmos pair and a transformer. This major qualifying project involves the design of a voltage controlled oscillator vco for radiofrequency rf applications.
A low phase noise kaband cmos voltagecontrolled oscillator is proposed in this paper. Lecture 25 negative resistance view, oscillator circuits ee142 fall 2010 nov. It can be shown that the colpitts family of oscillator never squegg. The negative conductance is decreased by the feedback factor. This letter proposes a differential common drain colpitts. Although both these oscillators oscillator use an lc tuned tank circuit to control the oscillator frequency, the hartley design can be recognised by its use of a tapped inductor l1 and l2 in fig. Colpitts oscillator in this configuration the active device is in a common base configuration. A new enhanced differential cmos colpitts oscillator. Colpitts oscillator is a type of lc oscillator which falls under the category of harmonic oscillator and was invented by edwin colpitts in 1918. For example, some of the current supplied by the transistor to overcome the loss in the resonator flows through c 2 making this topology less efficient than the differential lc oscillator. This differential oscillator outputs differential voltage signals that are about 180 degrees out of phase.
A colpitts oscillator is the electrical dual of a hartley oscillator, where the feedback signal is taken from an inductive voltage divider consisting of two coils in series or a tapped coil. Colpitts oscillator circuit diagram working and applications. Like most oscillator circuits, the colpitts oscillator exists in several forms, with the most common form being similar to the transistor circuit above. Then to summarise, the colpitts oscillator consists of a parallel lc resonator tank circuit whose feedback is achieved by way of a capacitive divider. The colpitts oscillator thus remains popular because it requires only a single pin to. It is type of feedback lc oscillator where feedback is supplied capacitively. Name equivalent circuit description 1 osc1 colpitts oscillator crystal connection. Cmos colpitts oscillator either singleended or differential, see fig.