Programmable Analog Array

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Chapter 4

• Programmable Analog Array

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The Field Programmable Analog Array (FPAA)

• What is a field-programmable analog array (FPAA)?
• A field-programmable analog array is an
  integrated circuit which can be configured to
  implement various analog functions using a set of
  configurable analog blocks (CAB) and a
  programmable interconnection network, and is
  programmed with the use of on-chip memories.

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The Field Programmable Analog Array (FPAA)

• A FPAA (Field Programmable Analog Array) is
  designed a freely programmable similar circuit,
  after the model of the FPGAs.
• A FPAA consists of a matrix of configurable
  similar blocks.
• Such a block is called CAB (Configurable similar
  to block).
• With a CAB different similar basic circuits can
  be realized such as filters or amplifiers.
• A logical circuit serves for manufacturing the
  necessary connections within and between the
  CABs.
• Similar entrances and exits make the connection
  to the external world.
• The configuration is made by digital entrances
  and exits, which can be attached to memory
  modules or microprocessors

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The Field Programmable Analog Array (FPAA)
Example of FPAA block
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The Field Programmable Analog Array (FPAA)

• A conceptual FPAA is shown in Figure 1. Included
  are the CABs, interconnection network, I/O
  blocks, and configuration bit string.

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The Field Programmable Analog Array (FPAA)
Figure 1 Generic FPAA Diagram
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The Field Programmable Analog Array (FPAA)

• Each CAB can implement a number of analog signal
• processing functions such as amplification,
  integration,
• differentiation, addition, subtraction,
  multiplication,
• comparison, log, and exponential.
• The interconnection network routes signals from
  one
• CAB to another, and to and from the I/O
  blocks.
• A configuration bit string stores the information
  used to
• configure the FPAA.

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The Field Programmable Analog Array (FPAA)
Why ANALOG ?
Real-world signals are in analog.

• Processing these signals in the analog domain has
  a few key advantages.
• First, there is no need for A/D and D/A
  converters, saving resources.
• Second, analog designs generally consume lower
  power than their digital counterparts. This is
  important in wireless applications where low
  power consumption is important.
• Third, analog designs potentially use less die
  area than their digital counterparts.

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The Field Programmable Analog Array (FPAA)
What are some FPAA design issues ?

• FPAAs are designed in both the continuous-time
  and discrete-time domains.
• A discrete-time FPAA, designed with
  switched-capacitor or switched-current technology
  has advantages in terms of programmability and
  insensitivity to resistance in programming
  switches, but is limited to signal frequencies
  significantly lower than the clock frequency.
• A continuous-time FPAA, usually designed using
  transconductors, has advantages in terms of
  bandwidth, but has a narrower programming range
  for its parameters, and its performance is prone
  to degradation from circuit parasitics.

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The Field Programmable Analog Array (FPAA)
What limits the frequency response of a given
FPAA ?

• Factors limiting the frequency performance of
  FPAAs include
• the bandwidth of op-amps used on the FPAA, and
• number of CABs to be cascaded.
• Discrete-time designs (switched-capacitor and
  switched-current) are limited by the maximum
  clocking frequency, which further limits the
  signal frequencies due to the Nyquist theorem.
• Also limiting FPAA frequencies are maximum
  comparator and transconductor frequencies. The
  above factors are illustrated in Figure 2

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The Field Programmable Analog Array (FPAA)
Figure 2 Factors Limiting FPAA Bandwidths
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The Field Programmable Analog Array (FPAA)
Figure 2 Factors Limiting FPAA Bandwidths
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The Field Programmable Analog Array (FPAA)

• The new FPAA technology provides an elegant way
  of implementing these designs with the added
  benefit of reconfiguration.
• The key benefits of an FPAA over a fixed-function
  solution are
• a greatly simplified design process
• a one-component solution for multiple designs,
  greatly simplifying inventory management
• an integrated design solutiondesign
  specifications are immune to temperature,
  process, and component aging and
• precision operation and increased system
  reliability