A kind of DC deviation bearing calibration of wireless intermediate frequency receiver circuit system
Technical field
The present invention relates in the semiconductor technology and circuit design technique in electronic engineering, particularly radio frequency (RF) circuit
Intermediate frequency (IF) receiving circuit system, and the complex bandpass filters that included and amplifier circuit module.
Background technology
Antenna (Antenna), low-noise amplifier (LNA), frequency mixer is generally included in radio frequency (RF) receiving circuit
(Mixer) modules such as, low pass filter (LPF), signal amplifier (VGA), analog-digital converter (ADC).If take directly turned
The mode of (Direct Conversion) is changed, and signal path is received in the frequency mixer stage and oscillator (LO) clock path is easy
Intercouple leakage, so causes self mixing and produces DC deviation.In order to avoid this problem, in being much designed with
Frequently the mode of (IF) circuit, that is, be divided into two stages to isolate original signal from RF signals.First stage is made in frequency mixer
It is mixed with the frequency for being slightly less than transmitting LO clocks, at this moment will be used complex bandpass filters (BPF) and amplifier (VGA)
To replace low pass filter (LPF) and amplifier (VGA) in directly conversion (Direct Conversion) circuit;Second-order
Section digitally decodes original signal in base band.The DC deviation that the frequency mixer of so intermediate frequency I/F circuit is caused drops significantly
Low, and the main source of DC deviation is no longer self mixing of mixer module, but other factors, such as difference channel are not right
Claim, process deviation etc., the gain of particularly circuit is especially apparent when big.
The difficult point of the DC deviation correction of wireless intermediate frequency receiver circuit system is:Due to intermediate-frequency circuit process is plural number
Frequency, so I passages and Q channel circuits have interaction feedback to act on.For detached I passages or Q passages, due to not feeding back to
The presence on road, DC deviation timing need to only sample output direct current biasing then carry out disposable current compensation just can be by direct current
Biasing drops to very low level.But for I passages and the interaction feedback of Q channel circuits, even if after I channel correctings, leading in correction Q
The direct current biasing of I passages may be allowed during road to return to very poor level.Even if being followed to I passages and Q passages repeatedly
Ring is corrected, and the direct current biasing of output end may not restrained, it is difficult to be reduced to preferable level.This is outstanding in the situation of high-gain
Its substantially, due to the sensitivity of at this moment circuit bigger.
A lot of at present wireless intermediate frequency receiver circuit systems are still adopted to complex bandpass filters (BPF) and amplifier
(VGA) I passages and the recirculation correction of Q passages, till then obtaining relatively small DC deviation (80mv-100mv),
Such that rear stage plural number band logical Δ ∑ analog-digital converter (ADC) of if bandpas filter (BPF) and amplifier (VGA)
Saturation is easy to, dynamic range of signals reduces, so as to reduce the performance of system;And this mode is inclined due to cannot ensure direct current
Difference arrives minimum of a value, so great DC deviation can be caused under the worst situation of technique, so will also result in chip yield
(Yield) decline.
Although some modes interfere with each other problem, such as high pass solving the DC deviation that I passages and Q passages are caused
(Qualcomm) United States Patent (USP)s US2011/0037506A1 in 2011, add out in the path that I passages and Q passages are coupled
Close control to separate the direct current biasing of sampling I passages and Q passages and be corrected, but this method has individual it is assumed that being exactly when I is logical
When road is identical with the direct current biasing level that the amplifier of Q passages is produced, adopts and direct current biasing can be dropped to extremely low level in this way.
But bandpass filter and amp DC biasing mechanism ability precisely due to some random factors, such as technique cause several
What size deviates, and symmetry is inadequate etc., so while direct current biasing can be reduced by this mode in most of situations, but
It is not a kind of reliable method.When I passages are different with the direct current biasing level of Q passages or during even opposite polarity, which school
Positive result is just undesirable.
Content of the invention
Based at present for wireless intermediate frequency receiver circuit system, including complex bandpass filters and the direct current biasing of amplifier
The integrity problem that circuit is present, the present invention is on the basis of strict theory analysis, it is proposed that a kind of reliable and stable including multiple
Count the correcting mode of bandpass filter and amplifier in the direct current biasing of interior wireless intermediate frequency receiver circuit system.
For the situation that I passages and Q passages in complex bandpass filters and amplifier intercouple, I passages are in wave filter
DC deviation with amplifier out is:
Wherein, Δ MIWith Δ MQBe I passages and Q passages complex bandpass filters and amplifier previous stage module produce straight
Stream bias, and Δ VIWith Δ VQIt is then that complex bandpass filters and amplifier sheet are produced in I passages and Q passage amplifiers input
Dc bias.Equally, Q passages in the Dc bias of wave filter and amplifier out are:
Above-mentioned analysis is based on, present invention design takes following manner inclined to reduce and offset direct current produced by intermediate-frequency circuit
Difference:
A. design R and R0 take same resistance come so thatThe DC deviation that item is generated is zero;This condition is easy to
Realize, because complex bandpass filters and amplifier circuit gain are determined by R/Ri, if R is fixed as R0 values, only can change
Ri is reaching the purpose (VGA) of variable gain;
B. increase I channel switch SWI, when such SWI is switched off Ri equivalent to ∞ so that DC deviation itemIt is zero;
C. increase Q channel switch SWQ, when such SWQ is switched off Ri equivalent to ∞ so that DC deviation item isZero;
Be based on above-mentioned analysis, the present invention design take following steps come realize reduce output end Dc bias to close to
Zero level:
A. when medium frequency reception and complex bandpass filters and amplifier system are designed using same resistance attenuated feedback
Resistance R and coupling frequency displacement resistance R0;So cause in I passages and Q passages output DC deviationIt is straight that item is generated
Stream deviation is zero;
B. I passages and Q channel signal input end switch SWI and SWQ are disconnected so that DC deviation itemWith
All it is zero;Iq1 current sources amplitude is adjusted using direct current biasing sampling feedback compensation circuit to compensate bias current
And I passages and Q channel DCs deviation are reduced to simultaneously close to zero;
C. disconnect Q channel signal input end switch to causeIt is zero, connects I path inputs switch, by sampling
Feedback circuit adjusts Ii2 current sources amplitude to compensate bias currentAnd I passages and Q channel DCs deviation are subtracted simultaneously
Little to close to zero;
D. I passages and Q path inputs switch is connected, and Iq2 current sources amplitude is adjusted by sampling feedback circuit to compensate
Bias currentAnd I passages and Q channel DCs deviation are reduced to simultaneously close to zero;
Above-mentioned analysis is based on, due to Δ MIWith Δ MQIt is the direct current produced by I passages and Q passages are exported in frequency mixer respectively
Deviation, so the correcting mode of the present invention includes DC deviation of the correction produced by low-noise amplifier and frequency mixer;
Above-mentioned analysis is based on, due to Δ VIWith Δ VQIt is complex bandpass filters and amplifier sheet respectively in I passages and Q
The Dc bias that passage amplifier input is produced, thus the correcting mode of the present invention include correction by complex bandpass filters and
The DC deviation that amplifier is produced;
Above-mentioned analysis is based on, the present invention is at plural band logical Δ ∑ analog-digital converter (Complex Band-pass Δ ∑ ADC)
Digital output end adopts baseband digitized direct current biasing sample averaging, calculates on the basis of many sub-sampling (1000-2000 time)
Go out the mean value of the DC deviation of the I passages and Q passages of last output, and pass through DC deviation feedback compensation circuit.So this
Invention correction result be so that whole intermediate-frequency circuit output DC deviation be reduced to the level close to zero, also include by
The DC deviation that plural band logical Δ ∑ analog-digital converter (ComplexBand-pass Δ ∑ ADC) is produced;
Though being not expressly mentioned, current source compensation way of the present invention can be single-ended or differential compensation.Lead in differential compensation
The electrode input end and negative input in road has compensating current element, and its amplitude is equal but opposite polarity.
The present invention is taken less than digital to analog converter (DAC) to the precision that the DC deviation of wireless intermediate frequency receiver circuit system is corrected
Lowest order (LSB) representated by DC deviation level.So the precision of D AC is higher, the precision of final DC deviation correction
Higher.
Description of the drawings
Fig. 1 is the built-up circuit module of wireless intermediate frequency receiver circuit system and signal path;
Fig. 2 is the access way of the circuit structure and DC offset correction current source of complex bandpass filters and amplifier;
Fig. 3 is the internal module figure of DC deviation feedback compensation circuit;
Fig. 4 is wireless intermediate frequency receiver circuit system dc correction for drift step;
Fig. 5 is the output waveform of DC deviation correcting process.
Following specific embodiment will be described with reference to the drawings.
Specific embodiment
The be suitable for wireless intermediate frequency receiver circuit system of DC deviation correcting mode of the present invention is as shown in Figure 1.RF signals by
Antenna (101) is entered, through low-noise amplifier (LNA, 102) after divide two-way send into frequency mixer (Mixer, 103 and 104), point
Jin Ru not I passages and Q passages;Next I passages and Q channel signals enter complex bandpass filters and amplifier (Complex
BPF and VGA, 105), through plural band logical Δ ∑ analog-digital converter (Complex Band-pass Δ ∑ ADC, 107) after become
Baseband signal.Baseband digitized DC deviation sample averaging module is calculated on the basis of many sub-sampling (1000-2000 time)
The I passages for finally exporting and the mean value of the DC deviation of Q passages, and pass through DC deviation feedback compensation circuit, in three times so
The output for generating control electric current source afterwards enters the input of complex bandpass filters and amplifier.Due to complex bandpass filters and
Amplifier is located at centre, so its direct current biasing is also affected by above frequency mixer and low-noise amplifier.
Fig. 2 is circuit structure and the access way in DC deviation correcting current source of complex bandpass filters and amplifier.
Design of circuit system part includes:
A. when medium frequency reception and wave filter and amplifier system are designed using same resistance attenuated feedback resistance R and coupling
Sum of fundamental frequencies moves resistance R0;
B. DC deviation correcting current compensation point has at three:Ii2 was accessed before I passage input resistance Ri, to eliminate
Come from the DC deviation of previous stage frequency mixer I passages output;Iq2 was accessed before Q passage input resistance Ri, was come with eliminating
From the DC deviation exported in previous stage frequency mixer I passages;Iq1 be after passage input resistance Ri access, with eliminate from
DC deviation in Q channel operation amplifier ins;
C. why the DC deviation of I channel operation amplifier ins need not compensate for (without current source Ii1) be because
It is the attenuated feedback resistance R of same resistance used in claim 2a and coupling frequency displacement resistance R0, so putting in I channel operations
It is zero that big device DC deviation is offset in the effect that output end is produced.
The module of DC deviation feedback compensation circuit includes in figure 3:
A.I passages and the digitlization of Q channel DCs deviation average judge
B. successive approximation register algorithm logic and corresponding register (SAR)
C. multidigit high precision digital-to-analog converter (DAC)
D. controlled current source
Aligning step that medium frequency reception wave filter and amplifier circuit DC deviation are fixed as shown in figure 4, including:
A. electric on chip, system initialization, so register sets initial value 0;By the positive and negative defeated of low-noise amplifier (LNA)
Enter to hold short circuit;
B. I passages and Q channel signal input end switch is disconnected, Iq1 compensating current element width is adjusted by sampling feedback circuit
Degree;
C. adjust Iq1 compensating current element amplitudes number of times and depend on multidigit high accuracy digital-to-analogue in DC deviation feedback compensation circuit
The bit number of converter (DAC), connects until the DC deviation mean value of baseband digital parts I passages and Q passages is reduced to simultaneously
It is bordering on zero;
D. Q channel signal input end switch is disconnected, connects I path inputs switch, Ii2 is adjusted by sampling feedback circuit
Compensating current element amplitude;
E. adjust Ii2 compensating current element amplitudes number of times and depend on multidigit high accuracy digital-to-analogue in DC deviation feedback compensation circuit
The bit number of converter (DAC), connects until the DC deviation mean value of baseband digital parts I passages and Q passages is reduced to simultaneously
It is bordering on zero;
F. I passages and Q path inputs switch is connected, Iq2 is adjusted by DC deviation feedback compensation circuit and is compensated electric current
Source amplitude;
G. adjust Iq2 compensating current element amplitudes number of times and depend on multidigit high accuracy digital-to-analogue in DC deviation feedback compensation circuit
The bit number of converter (DAC), connects until the DC deviation mean value of baseband digital parts I passages and Q passages is reduced to simultaneously
It is bordering on zero;
H. the positive-negative input end short circuit of low-noise amplifier (LNA) is disconnected;Medium frequency reception wave filter and amplifier circuit
DC deviation trimming process terminates.
Fig. 5 is the oscillogram of DC deviation in continuous three trimming processes.The DC deviation of I and Q passage is corrected each time
All zero is reduced to almost simultaneously.But when switch switching, the DC deviation of I passages and Q passages is deteriorated, so school next time again
DC deviation is reduced to almost zero again just.Finally when all opening, direct current biasing is reduced to several by correcting process
When being zero, the state at this moment switching is also the state of normal circuit operation, so during normal work, corrected after circuit
DC deviation also almost nil.
Current source compensation way of the present invention can be single-ended or differential compensation.The electrode input end of passage in differential compensation
There is compensating current element with negative input, its amplitude is equal but opposite polarity.
Specific embodiment for the present invention illustrated above, but protection scope of the present invention is not limited thereto.Any ripe
The professional and technical personnel of the art is known in technical scope disclosed by the invention, the change or replacement for being readily occurred in, all
Should be included within the scope of the present invention.