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Digital or Analog? How Ought to I and Q Combining and Separation Be Finished? – Technical Articles


Analog IQ Modulators (for transmitters) and IQ Demodulators (for receivers) have been used for many years ([1] to [3]).

the Not too long ago, new A/D and D/A Converters have been launched, which may instantly pattern an IF at from 1 to 4 GHz; sampling within the 2nd, third, and 4th Nyquist zones ([4] to [7]). These, mixed with increased pace digital logic, enable the combining (for A/D) and separation (for D/A) do be completed digitally ([8] to [21]). That is illustrated in Determine 1(a) (for a modulator) and Determine 1(b) (for a demodulator) with the Knowledge Converter (DAC or ADC) in place “D”.


Determine 1(a). Modulator


Determine 1(b). Demodulator


Then again, built-in analog I, Q combiners and separators have superb matching between the I and Q paths, fixing a number of the objections to doing these processes analogly. The analog approach additionally requires twice the info converters (A/Ds or D/As) than direct sampling at IF, however they run at decrease sampling charges; so they’re cheaper and require much less energy. That is illustrated in Determine 1(a) (for a modulator) and Determine 1(b) (for a demodulator) with the Knowledge Converter (DAC or ADC) in place “A”.

The creator beginning desirous about this query. He requested for opinions on a number of LinkedIn teams, and obtained useful solutions. With the approval of the acknowledgees, they’re acknowledged under. He additionally came upon no matter data he might on the properties of up to date Built-in Circuits (ICs) for these capabilities, and the outcomes of no matter efficiency necessities had been decided for these ICs. From this, he tried to generate no matter common conclusions could possibly be drawn to reply the query; “Ought to IQ Modulation and Demodulation be completed Analogly or Digitally?”


Analog IQ Strategy

The analog IQ method has been round for many years ([1] to [3]). Any IF or RF sign might be represented by


R(t) = I(t)cos(2πft) +Q(t)sin(2πft)


the place f is the provider frequency, I(t) known as the In-Part part, and Q(t) known as the Quadrature part. An analog IQ modulator takes the baseband indicators I(t) and Q(t) and varieties R(t). That is proven in Determine 1(a) with the DACs in place A. An analog IQ demodulator takes as enter R(t), and varieties I(t) and Q(t). That is proven in Determine 1(b) with the DACs in place A.

A crucial downside with the analog method is sustaining the good points via the 2 paths to be equivalent, and the section distinction to be precisely 90º. Generally uncared for for these necessities are the 2 Low Cross Filters. They need to be precisely acquire and phase-matched for all frequencies the place there may be vital sign vitality. Extra precise quantification of those necessities, and the impairments attributable to deviations from them, are proven in a later article.


Digital IQ Strategy

Latest developments in high-speed information converters (DACs and ADCs), have lead individuals to keep away from the IQ imbalance downside mentioned within the Analog IQ Strategy part by implementing the IQ Modulator and Demodulator capabilities digitally, the place the acquire and section might be produced with no error ([5], [8] to [21]). For the modulator case, there’s a high-speed DAC on the output, as proven in Determine 1(a) with the DAC in place D. For the demodulator case, there’s a high-speed ADC on the enter, as proven in Determine 1(b) with the ADC in place B.

Typically these digital approaches benefit from the aliasing impact, utilizing what known as bandpass sampling ([22] to [24]. [24A], [24B]). Determine 2(a) exhibits a waveform sampled in time. Determine 2(b) exhibits the spectra of the unsampled and sampled sign. The pattern clock of the ADC is performing the identical operate because the Native Oscillator in an RF mixer. For an ADC, an analog filter can enable solely a sign in a single Nyquist zone to move, and this mixing motion can be utilized to downconvert a sign in that Nyquist zone to baseband. 


Determine 2(a). Sampling in Time Area


Determine 2(b). The spectra of the unsampled and sampled sign


For DACs, the output might be formed in time to enhance the efficiency at increased frequencies.


Determine 3(a) exhibits a “Regular” or “Non-Return to Zero” (NRZ) DAC output. After every pattern, the output stays fixed till the subsequent pattern. The analog spectrum is proven in Determine 3(b).


Determine 3(a). Sampling in Time Area


Determine 3(b).


Determine 4(a) exhibits a “Return to Zero” (RZ) DAC output. After every pattern, the output stays fixed for half a pattern interval, after which goes to zero. This has the impact of accelerating the amplitude within the second Nyquist zone, as proven in Determine 4(b).


Determine 4(a). Sampling in Time Area


Determine 4(b).


Determine 5(a) exhibits a “Combine” or “RF” DAC output. After every pattern, the output stays fixed for half a pattern interval, after which goes to detrimental that worth. That is similar operation as a mixer which makes use of each polarities of the Native Oscillator waveform. The analog spectrum, proven in Determine 5(b), has an excellent bigger amplitude within the second Nyquist zone. After a waveform is created through any of the above strategies, the specified frequencies have to be filtered out with a Low-Cross or Band-Cross filter, to take away no matter undesired alias and spurious responses there could be.


Determine 5(a). Sampling in Time Area


Determine 5(b).


The digital method avoids any issues with quadrature imbalance. Nevertheless, all information converters have their very own undesired impartments, as a result of quantization and sampling results. A few of these results shall be proven within the subsequent article. The associated fee and energy necessities of those high-speed information converters are additionally usually excessive, in comparison with analog IQ networks.



When the questions addressed on this report first appeared within the creator’s thoughts, he solicited feedback via some LinkedIn teams. A number of helpful responses have been obtained. Those that gave permission for his or her private data for use are; Gary Kaatz, Khaled Sayed (Consultix-Egypt), Dieter Joos (ON Semiconductor), and Jaideep Bose (Asmaitha Wi-fi Applied sciences). The creator additionally thanks his spouse, Elizabeth, who in all probability puzzled what her husband was as much as; secluded in his house workplace, doing work he was apparently not being paid to do.



The next references shall be used for every of the articles on this sequence.


Analog IQ Modulators and Demodulators: Normal Descriptions

[1] Shou-Hsien Weng; Che-Hao Shen; Hong-Yeh Chang, “A large modulation bandwidth bidirectional CMOS IQ modulator/demodulator for microwave and millimeter-wave gigabit functions,” Microwave Built-in Circuits Convention (EuMIC), 2012 seventh European , vol., no., pp.8,11, 29-30 Oct. 2012

[2] Eamon Nash; “Correcting Imperfections in IQ Modulators to Enhance RF Sign Constancy “; Analog Units Utility Notice AN-1039; 2009

[3] Anon; “An IQ Demodulator-Primarily based IF-to-Baseband Receiver with IF and Baseband Variable Acquire and Programmable Baseband Filtering “; Analog Units Circuit Notice CN-0320; 2013


Excessive Velocity Knowledge Converters (DACs and ADCs); Normal Info

[4] Justin Munson; “Understanding Excessive Velocity DAC Testing and Analysis”; Analog Units Utility Notice AN-928; 2013

[5] Engel, G.; Fague, D.E.; Toledano, A, “RF digital-to-analog converters allow direct synthesis of communications indicators,” Communications Journal, IEEE, vol.50, no.10, pp.108, 116, October 2012

[6] Chris Pearson; “Excessive Velocity, Digital to Analog Converters Fundamentals”; Texas Devices Utility Report SLAA523A; 2012

[7] Alex Arrants, Brad Brannon and Rob Reeder; “Understanding Excessive Velocity ADC Testing and Analysis”; Analog Units Utility Notice AN-835, 2010.


Digital IQ Modulators and Demodulators

[8] Samueli, H.; Wong, B.C., “A VLSI structure for a high-speed all-digital quadrature modulator and demodulator for digital radio functions,” Chosen Areas in Communications, IEEE Journal on, vol.8, no.8, pp.1512,1519, Oct 1990

[9] Wong, B.C.; Samueli, H., “A 200-MHz all-digital QAM modulator and demodulator in 1.2-nm CMOS for digital radio functions,” Strong-State Circuits, IEEE Journal of, vol.26, no.12, pp.1970, 1980, Dec 1991

[10] Ken Gentile; “Digital Quadrature Modulator Acquire “; Analog Units Utility Notice AN-924; 2009

[11] Lou, J. H.; Kuo, J.B., “A 1.5-V CMOS all-N-logic true-single-phase bootstrapped dynamic-logic circuit appropriate for low provide voltage and high-speed pipelined system operation,” Circuits and Programs II: Analog and Digital Sign Processing, IEEE Transactions on, vol.46, no.5, pp.628,631, Might 1999

[12] Vankka, J.; Sommarek, J.; Ketola, J.; Teikari, I; Halonen, Okay. A I, “A digital quadrature modulator with on-chip D/A converter,” Strong-State Circuits, IEEE Journal of, vol.38, no.10, pp.1635, 1642, Oct. 2003

[13] Yanlin Wu; Dengwei Fu; Willson, A, “A 415 MHz direct digital quadrature modulator in 0.25-nm CMOS”, Customized Built-in Circuits Convention, Proceedings of the IEEE 2003, vol., no., pp.287,290, 21-24 Sept. 2003

[14] Sommarek, J.; Vankka, J.; Ketola, J.; Lindeberg, J.; Halonen, Okay., “A digital modulator with bandpass delta-sigma modulator,” Strong-State Circuits Convention, 2004. ESSCIRC 2004. Continuing of the thirtieth European, pp.159, 162, 21-23 Sept. 2004

[15] Lin, P.F.; Lou, J. H.; Kuo, J.B., “A CMOS quadrature modulator for wi-fi communication IC,” Circuits and Programs I: Elementary Principle and Purposes, IEEE Transactions on, vol.44, no.6, pp.559, 561, Jun 1997

[16] Parikh, V.Okay.; Balsara, P.T.; Eliezer, O.E., “All Digital-Quadrature-Modulator Primarily based Wideband Wi-fi Transmitters,” Circuits and Programs I: Common Papers, IEEE Transactions on, vol.56, no.11, pp.2487, 2497, Nov. 2009

[17] Alavi, M.S.; Staszewski, R.B.; de Vreede, L.C.N.; Lengthy, J.R., “A Wideband13-bit All-Digital I/Q RF-DAC,” Microwave Principle and Strategies, IEEE Transactions on, vol.62, no.4, pp.732, 752, April 2014

[18] Inkol, Robert and Saper, Ron; “Digital Quadrature Modulator for Radar ESM Purposes” Canadian DEFENCE RESEARCH ESTABLISHMENT OTTAWA TECHNICAL NOTE 92-10; 1992

[19] Ziomek, C.; Corredoura, P., “Digital I/Q demodulator,” Particle Accelerator Convention, 1995., Proceedings of the 1995 , vol.4, no., pp.2663,2665 vol.4,1-5 Might 1995

[20] Ho, Okay.C.; Chan, Y.T.; Inkol, R., “A digital quadrature demodulation system,” Aerospace and Digital Programs, IEEE Transactions on , vol.32, no.4,pp.1218,1227, Oct 1996

[21] Bravo, A; Cruz-Roldan, F., “Digital quadrature demodulator with 4 phases mixing for digital radio receivers,” Circuits and Programs II: Analog and Digital Sign Processing, IEEE Transactions on, vol.50, no.12, pp.1011,1015, Dec. 2003


Bandpass sampling (Rev .04 modified “subharmonic sampling” to “bandpass sampling)

[22] Parssinen, A; Magoon, R.; Lengthy, S.I; Porra, Veikko, “A 2-GHz subharmonic sampler for sign downconversion,” Microwave Principle and Strategies, IEEE Transactions on, vol.45, no.12, pp.2344, 2351, Dec 1997

[23] Jensen, B.S.; Schmidl Sobjaerg, S.; Skou, N.; Krozer, V., “Compact front-end prototype for subsequent technology RFI-rejecting polarimetric L-band radiometer,” Microwave Convention, 2009. EuMC 2009. European, vol., no., pp.1626, 1629, Sept. 29 2009-Oct. 1 2009

[24] Ahmed, S.; Saad El Dine, M.; Reveyrand, T.; Neveux, G.; Barataud, D.; Nebus, J. M., “Time-domain measurement system utilizing Observe & Maintain Amplifier utilized to pulsed RF characterization of excessive energy GaN gadgets,” Microwave Symposium Digest (MTT), 2011 IEEE MTT-S Worldwide , vol., no., pp.1,4, 5-10 June 2011

[24A] Akos, D.M.; Stockmaster, M.; Tsui, J. B Y; Caschera, J., “Direct bandpass sampling of a number of distinct RF indicators,” Communications, IEEE Transactions on , vol.47, no.7, pp.983,988, Jul 1999

[24B] Ching-Hsiang Tseng; Solar-Chung Chou, “Direct downconversion of a number of RF indicators utilizing bandpass sampling,” Communications, 2003. ICC ’03. IEEE Worldwide Convention on , vol.3, no., pp.2003,2007 vol.3, 11-15 Might 2003


Results of IQ Imbalance, no compensation or exploitation proposed

[25] Lopez-Martinez, F.J.; Martos-Naya, E.; Paris, J.F.; Entrambasaguas, J.T., “Actual Closed-Kind BER Evaluation of OFDM Programs within the Presence of IQ Imbalances and ICSI,” Wi-fi Communications, IEEE Transactions on, vol.10, no.6, pp.1914, 1922, June 2011

[26] Yaning Zou; Valkama, M.; Renfors, M., “Efficiency Evaluation of Area-Time Coded MIMO-OFDM Programs Underneath I/Q Imbalance,” Acoustics, Speech and Sign Processing, 2007. ICASSP 2007. IEEE Worldwide Convention on, vol.3, no., pp.III-341, III-344, 15-20 April 2007

[27] Chia-Liang Liu, “Impacts of I/Q imbalance on QPSK-OFDM-QAM detection,” Shopper Electronics, IEEE Transactions on, vol.44, no.3, pp.984, 989, Aug 1998

[28] Heung-Gyoon Ryu, “Range Impact of OFDM Communication with IQ Imbalance within the Rayleigh Fading Channel,” Communication Software program and Networks, 2010.ICCSN ’10. Second Worldwide Convention on, vol., no., pp.489, 493, 26-28 Feb. 2010

[29] Stroet, P.; “Measuring Part and Delay Errors Precisely in I/Q Modulators”; Linear Know-how Utility Notice 102; AN102-1; October 2005

7.6 Results of IQ Imbalance, compensation or exploitation proposed

[30] Tarighat, A; Sayed, AH, “Joint compensation of transmitter and receiver Impairments in OFDM techniques,” Wi-fi Communications, IEEE Transactions on, vol.6, no.1, pp.240, 247, Jan. 2007

[31] Marey, Mohamed; Steendam, Heidi, “Novel Knowledge Detection and Channel Estimation Algorithms for BICM-OFDMA Uplink Asynchronous Programs within the Presence of IQ Imbalance,” Wi-fi Communications, IEEE Transactions on , vol.13, no.5, pp.2706,2716, Might 2014

[32] Narasimhan, B.; Narayanan, S.; Minn, H.; Al-Dhahir, N., “Decreased-complexity baseband compensation of joint Tx/Rx I/Q imbalance in cellular MIMO-OFDM,” Wi-fi Communications, IEEE Transactions on , vol.9, no.5, pp.1720,1728, Might 2010

[33] Ozdemir, O.; Hamila, R.; Al-Dhahir, N., “I/Q Imbalance in A number of Beamforming {OFDM} Transceivers: SINR Evaluation and Digital Baseband Compensation,” Communications, IEEE Transactions on, vol.61, no.5, pp.1914, 1925, Might 2013

[34] Inamori, M.; Bostamam, AM.; Sanada, Y.; Minami, H., “IQ imbalance compensation scheme within the presence of frequency offset and dynamic DC offset for a direct conversion receiver,” Wi-fi Communications, IEEE Transactions on , vol.8, no.5, pp.2214,2220, Might 2009

[35] Tarighat, A; Sayed, AH., “MIMO OFDM Receivers for Programs With IQ Imbalances,” Sign Processing, IEEE Transactions on , vol.53, no.9, pp.35833596, Sept. 2005

[36] Hai Lin; Yamashita, Okay., “Subcarrier allocation based mostly compensation for provider frequency offset and I/Q imbalances in OFDM techniques,” Wi-fi Communications, IEEE Transactions on, vol.8, no.1, pp.18,23, Jan. 2009

7.7 Necessities for BaseBand DACs and ADCs

[37] Suno-Gained Chung; Seung-Yoon Lee; Kyu-Ho Park, “An energy-efficient OFDM ultra-wideband digital radio structure,” Sign Processing Programs, 2004. SIPS 2004. IEEE Workshop on, vol., no., pp.211, 216, 13-15 Oct. 2004


Necessities for RF DACS and ADCs; and for RF Non-linearities

[38] de Mateo Garcia, J.C.; Armada, AG., “Results of bandpass sigma-delta modulation on OFDM indicators,” Shopper Electronics, IEEE Transactions on , vol.45, no.2, pp.318,326, Might 1999

[39] Maurer, L.; Schelmbauer, W.; Pretl, H.; Springer, A; Adler, B.; Boos, Z.; Weigel, R., “Affect of receiver entrance finish nonlinearities on W-CDMA indicators,” Microwave Convention, 2000 Asia-Pacific, vol., no., pp.249, 252, 2000

[40] Kitaek Bae; Changyong Shin; Powers, E.J., “Efficiency Evaluation of OFDM Programs with Chosen Mapping within the Presence of Nonlinearity,” Wi-fi Communications, IEEE Transactions on , vol.12, no.5, pp.2314,2322, Might 2013

[41] Mahim Ranjan; Larson, L.E., “Distortion Evaluation of Extremely-Wideband OFDM Receiver Entrance-Ends,” Microwave Principle and Strategies, IEEE Transactions on, vol.54, no.12, pp.4422, 4431, Dec. 2006


7.9 Provider aggregation for LTE-advanced; Wideband spectral necessities.

[42] Pedersen, Okay.I; Frederiksen, F.; Rosa, C.; Nguyen, H.; Garcia, L.G.U.; Yuanye Wang, “Provider aggregation for LTE-advanced: performance and efficiency features,” Communications Journal, IEEE , vol.49, no.6, pp.89,95, June 2011


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