Advanced Design System - 2002_Circuit Envelope Simulation

Topic 8:

Circuit Envelope Simulation

ADS 2002 Fundamentals - April, 2002

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What is Circuit Envelope ? Time samples the modulation envelope (not carrier) Compute the spectrum at each time sample Output a time-varying spectrum Use equations on the data Faster than HB or Spice in many cases Integrates with System Simulation & HP Ptolemy

Next, what tests can it perform?ADS 2002 Fundamentals - April, 2002

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Test circuits with realistic signalsGSM, CDMA, GMSK, pi/4DQPSK, QPSK, etc.Simulations can include:–– – – –

Example CE results:

32.8 kHz BW for NADC

Adjacent Channel Power Ratio Noise Power Ratio Error Vector Magnitude Power Added Efficiency Bit Error Rate

2-tone tests and linearized models do not predict this behavior as easily!Also, Envelope can be used for PLL simulations: lock time, spurious signals, modulation in the loop.

890 MHz

carrierNext, how it works...ADS 2002 Fundamentals - April, 2002

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Circuit Envelope TechnologyCircuit

Vout

V(t) * e j2 fott3Modulation

t2

t1

t4

Time sample the envelope and then perform Harmonic Balance on the samples!More...

Carrier

Periodic input signalNOTE: V(t) can be complex - am or fm or pmADS 2002 Fundamentals - April, 2002

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…more on CE Technology

Next, an example...

Captures time and frequency characteristics:

dBm (fs (Vout))

ADS 2002 Fundamentals - April, 2002

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Example: AMP with RF pulse

You will do this in the lab!Step time is critical for sampling the envelope: rise, fall, and modulation rate. Therefore, Step (sample time) is NOT the same as Transient.

mag of Vin [1]: envelope ts of Vout: signal mag of Vout [1]: envelope...where [1] is the carrier: Freq[1].

Next, the controller setup...

ADS 2002 Fundamentals - April, 2002

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Envelope Setup tab in the controllerExample: one tone with 3 harmonicsStop time – Determines resolution bandwidth of output spectrum – Large enough to resolve spectral components of interest Time step – Determines bandwidth of Circuit Envelope simulation – Small enough to capture highest modulation frequency

Stop Time Resolution BW

Time step

moreModulation BW

ADS 2002 Fundamentals - April, 2002

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Envelope Setup tab (continued)LAB

7 Harmonics of Fundamental: Freq [1] 3 Harmonics of Fundamental: Freq [2]Harmonic Balance

Example: multiple tones with mixing

t0 t1 t2 t3 t4

Multiple tone simulation requires more time and more data display memory.ADS 2002 Fundamentals - April, 2002

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What the lab is about ...

Lab 8:

Circuit Envelope Simulations

ADS 2002 Fundamentals - April, 2002

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Steps in the Design Process Design the RF sys behavioral model receiver Test conversion gain, spectrum, etc. Start amp_1900 design – subckt parasitics Simulate amp DC conditions & bias network Simulate amp AC response - verify gain Test amp noise contributions

– tune parameters Simulate amp S-parameter response Define amp matching topology and tune input Optimize the amp in & out matching networks Filter design – lumped 200MHz LPF Filter design – microstrip 1900 MHz BPF Transient and Momentum filter analysis Amp spectrum, delivered power, Zin - HB Test amp comp, distortion, two-tone, TOI CE basics for spectrum and baseband CE for amp_1900 with GSM source Replace amp and filters in rf_sys receiver Test conversion gain, NF, swept LO power Final CDMA system test CE with fancy DDS Co-simulation of behavioral system

You are here:

ADS 2002 Fundamentals - April, 2002

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First, simulate using an RF pulseUse a behavioral amp and different time steps:

1 nsec vs 10 ns

Add distortion: get odd harmonics out-of-phase!

Set behavioral Amp into compression.

ADS 2002 Fundamentals - April, 2002

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Next, use a GSM source and demodulatorsPlot:bits_out and fm_demod

Plot the GSM BW spectrum with with and without windowing.

Also, insert a filter at Vin to alter the phase. See the difference at fm_demods.

ADS 2002 Fundamentals - April, 2002

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Finally, use AMP_1900 with the GSM sourcevariable t_step = 1 / (5X BW of GSM)

Plot the GSM spectrum

Verify baseband integrity using an equation to demodulate the signal:

ADS 2002 Fundamentals - April, 2002

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Optional - channel power calculationOn a new page in DDS, write two equations: limits defines the bandwidth and channel_pwr calculates power in the channel.

No need to resimulate, simply use Vout[1] which is 1900 MHz!

Start the lab now!

ADS 2002 Fundamentals - April, 2002

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