CN-116505880-B - VCO amplitude calibration circuit

CN116505880BCN 116505880 BCN116505880 BCN 116505880BCN-116505880-B

Abstract

The invention discloses a VCO amplitude calibration circuit, which belongs to the field of integrated circuit chips and comprises a selector, an amplitude detection module, an amplitude comparator, a digital state machine, a numerical control current source and an amplitude control module, wherein the selector, the amplitude detection module, the amplitude comparator, the digital state machine, the numerical control current source and the amplitude control module are sequentially connected to form the amplitude calibration circuit, the input of the selector is connected to the output end of the VCO, and the output of the amplitude control module is connected to the base electrode of a cross coupling tube of a voltage-controlled oscillator to form a whole loop. The invention replaces the traditional tail current tube current control strategy, adopts a current replication mode to control the current of the resonant cavity, eliminates the limit of the tail current tube on the output amplitude, and avoids Q value degradation and phase noise degradation caused by the energy loss of the second harmonic at the second harmonic frequency by the resonance of the tail inductance and the tail capacitance, so the invention can realize the rapid stable calibration under the conditions of better phase noise level and larger output swing.

Inventors

YANG JUNHAO
ZHAO ZILU
QIN ZHANMING
ZHANG QINFENG

Assignees

中国电子科技集团公司第五十八研究所

Dates

Publication Date: 20260512
Application Date: 20230420

Claims (5)

1. The VCO amplitude calibration circuit is characterized by comprising a selector, an amplitude detection module, an amplitude comparator, a digital state machine, a numerical control current source and an amplitude control module; The system comprises a selector, an amplitude detection module, an amplitude comparator, a digital state machine, a numerical control current source and an amplitude control module, wherein the selector, the amplitude detection module, the amplitude comparator, the digital state machine, the numerical control current source and the amplitude control module are sequentially connected to form an amplitude calibration circuit; the selector selects and outputs an oscillation signal of an enabling VCO in the broadband multi-core VCO; the amplitude detection module converts the high-frequency oscillation signal output by the VCO into a direct-current amplitude detection signal in proportional relation with the amplitude; the amplitude comparator is used for comparing the direct current amplitude detection signal with the reference voltage and outputting high and low levels as comparison results; The digital state machine detects the output high-low level comparison result and adjusts the output current control word; The numerical control current source generates adjustable output current controlled by an input current control word; The amplitude control module copies the current proportion output by the numerical control current source into the VCO resonant cavity, and controls the current of the VCO so as to control the oscillation amplitude of the VCO; The amplitude control module comprises cross coupling tubes Q41 and Q42, base blocking capacitors C41 and C42, a current replication triode Q43, two tail inductors L TAIL , two tail capacitors C TAIL , a negative feedback tube Q44, a bias resistor Rb and a pair of bias resistors R41 and R42; One ends of bias resistors R41 and R42 are respectively connected with bases of cross coupling transistors Q41 and Q42, and the other ends of bias resistors R41 and R42 are connected with a base of a current replication triode Q43 and one end of a bias resistor Rb, a collector of the current replication triode Q43 is connected with an output of the numerical control current source and a base of a negative feedback tube Q44, an emitter of the current replication triode Q43 is connected with one end of a tail inductor L TAIL and one end of a tail capacitor C TAIL , and a collector of the negative feedback tube Q44 is connected with a power supply VCC; One ends of base blocking capacitors C41 and C42 are respectively connected with bases of cross coupling tubes Q42 and Q41, and the other ends are respectively connected with collectors of the cross coupling tubes Q41 and Q42, emitters of the cross coupling tubes Q41 and Q42 are connected with one end of the other tail inductor L TAIL and one end of the other tail capacitor C TAIL ; The other ends of the two tail inductors L TAIL and the two tail capacitors C TAIL are grounded; The current proportion of the numerical control current source is copied into the VCO resonant cavity by the current copying triode Q43 through the bias resistors R41 and R42, the tail inductance L TAIL and the tail capacitance C TAIL of the emitter of the current copying triode Q43 are used for matching the working voltage of the current copying triode Q43 and the working voltage of the VCO cross coupling tube to be consistent, the negative feedback tube Q44 forms a negative feedback path from the collector of the current copying triode Q43 to the base, the output current of the numerical control current source is increased, the base voltage of the negative feedback tube Q44 is increased, the output current is increased, and therefore the base current and the collector current of the current copying triode Q43 are changed, and the circuit reaches a balanced state again.
2. The VCO amplitude calibration circuit of claim 1, wherein the amplitude detection module comprises a pair of coupling capacitors C21 and C22, an amplitude modulation capacitor C23, a pair of bias resistors R21 and R22, a pair of detection transistors Q21 and Q22, a tail current tube M21, a filter capacitor Cout; The upper polar plates of the coupling capacitors C21 and C22 are respectively connected to the output ends VOUTN and VOUTP of the VCO, the lower polar plates are respectively connected with the bases of the detection triodes Q21 and Q22, the bias voltage Vb1 is respectively connected to the bases of the detection triodes Q21 and Q22 through the bias resistors R21 and R22 to provide direct current bias voltage, the amplitude modulation capacitor C23 is connected between the bases of the detection triodes Q21 and Q22, the emitters of the detection triodes Q21 and Q22 are connected with the drain electrode of the tail current tube M21 and the upper polar plate of the filter capacitor Cout, the collectors of the detection triodes Q21 and Q22 are both connected with the power supply VCC, the source electrode of the tail current tube M21 is grounded, and the grid electrode is connected with the fixed bias voltage Vb2.
3. The VCO amplitude calibration circuit of claim 2, wherein the coupling capacitors C21 and C22 couple the differential large signal output by the VCO into the amplitude detection module, the amplitudes of the base oscillation signals of the detection transistors Q21 and Q22 are adjusted by adjusting the proportional relationship between the coupling capacitor and the amplitude modulation capacitor C23, the bias resistors R21 and R22 are used for determining the base dc bias voltage of the detection transistors, the tail current tube M21 is used for determining the bias current of the detection transistors, the filter capacitor Cout filters the ac component in the dc signal output by the amplitude detection module, and the capacitance values of the coupling capacitors C21 and C22 are equal.
4. The VCO amplitude calibration circuit of claim 1, wherein the digitally controlled current source comprises a bias transistor M BIAS , a bias resistor R BIAS , a current transistor M0, nine adjustable current mirrors M1-M9, nine current mirror adjustment switching tubes M A1 -M A9 , nine pull-up tubes M B1 -M B9 , nine bias resistors R0-R9; The drain electrode of the bias transistor M BIAS is connected with the grid electrode of the bias transistor M BIAS to form a voltage bias structure, the source electrode of the bias transistor M BIAS is connected with the bias resistor R BIAS , and the bias current I BIAS is input from the drain electrode of the bias transistor M BIAS ; the grid electrode of the current transistor M0 is connected with the grid electrode of the bias transistor M BIAS , the source electrode is connected with the bias resistor R0, and the drain electrode is connected with the output node; The drains of the current mirror adjusting switch transistors M A1 -M A9 are connected with the grid of the bias transistor M BIAS , the sources of the pull-up transistors M B1 -M B9 are connected to a power supply, the control signals ADJ 1 -ADJ 9 are respectively connected with the grid of the current mirror adjusting switch transistors M A1 -M A9 , and the control signals ADJ 1 -ADJ 9 are respectively connected with the grid of the pull-up transistor M B1 -M B9 after being inverted by an inverter.
5. The VCO amplitude calibration circuit of claim 4 wherein the dimensions of the adjustable current mirrors M1-M9 are proportional to the magnitude of the output current weights, and the corresponding bias resistors R1-R9 are also correspondingly proportional to ensure that the source voltages of each adjustable current mirror M1-M9 are the same; The current transistor M0 and the bias transistor M BIAS provide a part of fixed current as a fixed current bias, and the nine current mirror adjusting switch transistors M A1 -M A9 and the nine pull-up transistors M B1 -M B9 form a control module of nine adjustable current mirrors M1-M9 to control whether the adjustable current mirrors are connected to the bias transistor M BIAS to provide adjustable current, and the total output current is the sum of the fixed current and the numerical control adjustable current.

Description

VCO amplitude calibration circuit Technical Field The invention relates to the technical field of integrated circuit chips, in particular to a VCO amplitude calibration circuit. Background The VCO (Voltage Controled Oscillator, voltage controlled oscillator) is located at the output end of the PLL system, and is the module with the highest operating frequency in the PLL loop, the input signal is the voltage controlled voltage signal generated by the loop filter, and the output signal is the periodic oscillating signal with the frequency f OUT. The output signal frequency of the VCO is regulated by an input voltage-controlled voltage and is essentially a nonlinear circuit that converts an input dc signal to an output ac signal. For an amplitude calibration circuit, an increase in the oscillation amplitude of the output signal of the VCO can reduce the phase noise, and thus the phase noise can be effectively reduced by increasing the current and thus the amplitude in the current limited region. However, when the VCO enters the voltage limiting region, the Q value of the resonant cavity is lowered due to the decrease in current efficiency, which may lead to deterioration of phase noise, since the amplitude is not much changed with the increase in current. Therefore, when the circuit is biased at the critical point Vopt of the current limited region and the voltage limited region, the circuit can ensure the highest current efficiency and the optimal phase noise performance. An automatic amplitude calibration (Automatic Amplitude Caliberation, AAC) circuit is typically designed in low phase noise VCO designs so that the oscillation amplitude of the VCO at PVT remains around an optimal value to optimize phase noise performance. The amplitude calibration circuit of a conventional VCO typically achieves current flow to the resonant cavity by controlling the VCO tail current flow to better determine the oscillation signal swing. The tail current tube has a simple structure and is suitable for both NMOS and CMOS negative resistance VCOs. Meanwhile, during alternating current equivalent analysis, the tail current source is equivalent to a high resistance and is regarded as an open circuit, so that circuit energy loss caused by the fact that a cross coupling tube enters a linear region in the VCO oscillation process can be avoided. However, the high resistance equivalent of the tail current source is only established when the current tube works in the saturation region, when the oscillation swing is large, so that one cross-coupled tube works in the linear region and is equivalent to one low resistance, the other cross-coupled tube works in the cut-off region, and the lower source voltage of the cross-coupled tube in the linear region forces the tail current tube to enter the linear region, so that a low resistance passage from the resonant cavity to the ground through the two linear tubes of the cross-coupled tube in the linear region and the tail current tube is formed, which is equivalent to connecting one low resistance to the ground in parallel with the LC resonant cavity, and the equivalent parallel impedance of the resonant cavity is reduced, thereby reducing the Q value and deteriorating the phase noise. However, the tail current tube may introduce phase noise into the cavity while the overdrive voltage of the tail current tube may reduce the output swing of the VCO. Disclosure of Invention The invention aims to provide a VCO amplitude calibration circuit to solve the problems in the background art. In order to solve the technical problems, the invention provides a VCO amplitude calibration circuit, which comprises a selector, an amplitude detection module, an amplitude comparator, a digital state machine, a numerical control current source and an amplitude control module; The system comprises a selector, an amplitude detection module, an amplitude comparator, a digital state machine, a numerical control current source and an amplitude control module, wherein the selector, the amplitude detection module, the amplitude comparator, the digital state machine, the numerical control current source and the amplitude control module are sequentially connected to form an amplitude calibration circuit; the selector selects and outputs an oscillation signal of an enabling VCO in the broadband multi-core VCO; The amplitude detection module converts the high-frequency oscillation signal output by the VCO into a direct current amplitude detection signal in proportional relation with the amplitude; the amplitude comparator is used for comparing the direct current amplitude detection signal with the reference voltage and outputting high and low levels as comparison results; The digital state machine detects the output high-low level comparison result and adjusts the output current control word; The numerical control current source generates adjustable output current controlled by an input current control word; the amplitude co