A widely tunable continuous-time LPF for a direct conversion DBS Tuner تهیه و تنظیم : امین قرداشخانی
direct conversion DBS tuner <ul><li>In a direct conversion DBS tuner (Fig. 1), I/Q </li></ul><ul><li>broadband mixers down...
The baseband LPF specification from system requirements , A: <ul><li>moderate pass band ripple + sharp transition band </l...
The baseband LPF specification from system requirements,  B: <ul><li>Since there is no filtering until the baseband LPF, t...
2. System design considerations <ul><li>2.1 About the main filter topology </li></ul><ul><li>2.2 About corner frequency pr...
2.1 About the main filter topology <ul><li>a 7th-order Butterworth leapfrog Gm-C filter topology: </li></ul><ul><li>A leap...
2.2 About on chip automatic tuning   <ul><li>System specifications requires that the -3dB cutoff </li></ul><ul><li>frequen...
<ul><li>To guarantee  accurate and stable filtering  characteristic, </li></ul><ul><li>on-chip automatic frequency tuning ...
3. Circuit design <ul><li>Gm cell </li></ul><ul><li>Main filter </li></ul><ul><li>the biquad ICF </li></ul><ul><li>the DAC...
Gm cell <ul><li>Gm </li></ul>
Gm cell <ul><li>1.most critical for the whole filter and tuning system design </li></ul><ul><li>2. should have large enoug...
<ul><li>(a)  input range:96mv peak-to-peak differential +(THD) greater than 1 percent (-40dB). </li></ul><ul><li>(b)  inpu...
Main  filter: <ul><li>The structure and the component values of the  7th-order </li></ul><ul><li>Butterworth leapfrog Gm-C...
the biquad ICF: <ul><li>The low-pass transfer functions are (1) </li></ul><ul><li>The pole frequency wo, the filter qualit...
the DAC: <ul><li>The 7-bit DAC is a current-steering type linear DAC </li></ul><ul><li>IDACh and IDACI are the DAC's high ...
the phase-detector: <ul><li>A current-output Gilbert multiplier type phase detector </li></ul><ul><li>followed by two on-c...
Simulation result <ul><li>When its control current I_filter from the 7-bit </li></ul><ul><li>DAC is swept from 10 uA to 10...
Simulation result <ul><li>a </li></ul>
Conclusion <ul><li>A  high frequency and widely tunable continuous-time </li></ul><ul><li>low pass filter  has been implem...
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  1. 1. A widely tunable continuous-time LPF for a direct conversion DBS Tuner تهیه و تنظیم : امین قرداشخانی
  2. 2. direct conversion DBS tuner <ul><li>In a direct conversion DBS tuner (Fig. 1), I/Q </li></ul><ul><li>broadband mixers down-convert a cluster of channels from </li></ul><ul><li>the L-band (950MHz-2150MHz) directly to baseband. The </li></ul><ul><li>baseband I/Q LPFs select the desired channel signal, which </li></ul><ul><li>is then converted to digital bits through ADCs in the digital </li></ul><ul><li>demodulator chip for further processing </li></ul>
  3. 3. The baseband LPF specification from system requirements , A: <ul><li>moderate pass band ripple + sharp transition band </li></ul><ul><li>large stop band attenuation + moderate group delay ripple </li></ul><ul><li>3. Since the DBS channel date rate can vary from 1 to 45Msps, the cutoff frequency of the channel selection LPF should be tunable from 4MHz to 40MHz to cut off the closely spaced unwanted neighbor channel interferences. </li></ul><ul><li>4. An automatic tuning system is needed to maintain the precise filtering characteristics against process variation, temperature drift and aging. </li></ul>
  4. 4. The baseband LPF specification from system requirements, B: <ul><li>Since there is no filtering until the baseband LPF, the LPF itself should be very linear </li></ul><ul><li>the blocker signals can be only 20 dB stronger than the desired channel </li></ul><ul><li>3. System simulations indicate that a baseband VGA </li></ul><ul><li>should be placed in front of the LPF to optimal noise and linearity line-up </li></ul><ul><li>4 . So the noise specification of the LPF is </li></ul><ul><li>not so challenge and can be compromised for lower power consumption. </li></ul>
  5. 5. 2. System design considerations <ul><li>2.1 About the main filter topology </li></ul><ul><li>2.2 About corner frequency programmability and on chip automatic tuning </li></ul>
  6. 6. 2.1 About the main filter topology <ul><li>a 7th-order Butterworth leapfrog Gm-C filter topology: </li></ul><ul><li>A leapfrog realization of a low pass filter has lower </li></ul><ul><li>sensitivities of the pass band frequency response to </li></ul><ul><li>individual element values than a cascaded biquads realization </li></ul><ul><li>The Gm-C topology is usually preferred at high </li></ul><ul><li>frequency for its lower power consumption relative to </li></ul><ul><li>active-RC or MOSFET-C structures. </li></ul><ul><li>If implemented in bipolar or BiCMOS technology, the </li></ul><ul><li>Gm cells can be accurate tuned through bias current </li></ul><ul><li>variation as they depend directly on a linear gm-Ic </li></ul><ul><li>relationship, the fundamental translinear behavior of the </li></ul><ul><li>bipolar junction transistor. As a result, Gm-C filter's cutoff </li></ul><ul><li>frequency, which is proportional to GmlC, can have a wide </li></ul><ul><li>tuning range </li></ul>
  7. 7. 2.2 About on chip automatic tuning <ul><li>System specifications requires that the -3dB cutoff </li></ul><ul><li>frequency fo of the LPF can be digital programmed from 4MHz to 40MHz </li></ul><ul><li>2. the switching step should be as fine </li></ul><ul><li>as possible to cut off the closely spaced unwanted neighbor </li></ul><ul><li>channel interferences. </li></ul><ul><li>3. we can use a linear current DAC to achieve digital programmability with a fine step. </li></ul><ul><li>4. cutoff frequency of the main filter can be programmed </li></ul><ul><li>within the DAC's resolution </li></ul>
  8. 8. <ul><li>To guarantee accurate and stable filtering characteristic, </li></ul><ul><li>on-chip automatic frequency tuning is needed. In the </li></ul><ul><li>proposed design, a master-slave tuning system locks the </li></ul><ul><li>main filter's frequency response to a reference clock signal. </li></ul><ul><li>The PLL-based on chip automatic tuning system is shown </li></ul><ul><li>in Fig.2 . </li></ul>
  9. 9. 3. Circuit design <ul><li>Gm cell </li></ul><ul><li>Main filter </li></ul><ul><li>the biquad ICF </li></ul><ul><li>the DAC </li></ul>
  10. 10. Gm cell <ul><li>Gm </li></ul>
  11. 11. Gm cell <ul><li>1.most critical for the whole filter and tuning system design </li></ul><ul><li>2. should have large enough linear input range, </li></ul><ul><li>3. reasonable low noise and wide bandwidth </li></ul><ul><li>4. easily tunable and low power consumption </li></ul><ul><li>5. able to operate with 3.3-V supply </li></ul>
  12. 12. <ul><li>(a) input range:96mv peak-to-peak differential +(THD) greater than 1 percent (-40dB). </li></ul><ul><li>(b) input signal of about 200 mVppd for better than (-40dB)THD +only suitable for operation with 5-V supply voltage. </li></ul><ul><li>(c) signal capacity of 300mVppd for better than (-40dB) THD. +can be operating with 3.3-V supply voltage. </li></ul>
  13. 13. Main filter: <ul><li>The structure and the component values of the 7th-order </li></ul><ul><li>Butterworth leapfrog Gm-C filter are derived from the </li></ul><ul><li>double terminated LC ladder LPF prototype by signal flow </li></ul><ul><li>graph transformation. </li></ul><ul><li>The control current is mirrored to the tail </li></ul><ul><li>currents of the Gm cells with different scaling ratios based </li></ul><ul><li>on their individual Gm values </li></ul><ul><li>Voltage routing techniques is used to improve the matching between the Gm cells, which requires a careful layout floor planning to properly </li></ul><ul><li>route the base voltage bias line Vtune </li></ul>
  14. 14. the biquad ICF: <ul><li>The low-pass transfer functions are (1) </li></ul><ul><li>The pole frequency wo, the filter quality factor Q and the </li></ul><ul><li>gain at the pole frequency of the biquad are (2) </li></ul><ul><li>At the pole frequency, the output of the ICF is </li></ul><ul><li>in quadrature to its input. </li></ul><ul><li>The proper functioning of the PLL requires us to choose Gm1=Gmin=0.5Gm2=6GmT to make a moderate Q=8.4 </li></ul>
  15. 15. the DAC: <ul><li>The 7-bit DAC is a current-steering type linear DAC </li></ul><ul><li>IDACh and IDACI are the DAC's high and low reference current, </li></ul><ul><li>its transfer characteristic independent of process variation and temperature drift, and depends only on elements matching </li></ul><ul><li>So a careful layout is also important here </li></ul>
  16. 16. the phase-detector: <ul><li>A current-output Gilbert multiplier type phase detector </li></ul><ul><li>followed by two on-chip anti-parallel integrating </li></ul><ul><li>capacitors to form an integrator </li></ul><ul><li>An OTA converts the differential output voltage of the integrator into a single end current signal which combines with a constant </li></ul><ul><li>bleeding current to derive the biquad ICF's control current </li></ul><ul><li>and the DAC's reference currents </li></ul>
  17. 17. Simulation result <ul><li>When its control current I_filter from the 7-bit </li></ul><ul><li>DAC is swept from 10 uA to 100 uA, the filter's cut off </li></ul><ul><li>frequency is swept from 4.02MHz to 39.8MHz </li></ul>
  18. 18. Simulation result <ul><li>a </li></ul>
  19. 19. Conclusion <ul><li>A high frequency and widely tunable continuous-time </li></ul><ul><li>low pass filter has been implemented in a 0.35um SiGe </li></ul><ul><li>BiCMOS technology. A novel on chip automatic tuning </li></ul><ul><li>scheme has been successfully realized. The simulation </li></ul><ul><li>results show that the filter system is well suited for a direct </li></ul><ul><li>conversion DBS tuner </li></ul>
  20. 20. thanks

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