PMODIA_RM [ETC]

Digilent PmodIAâ¢ Impedance Analyzer Reference Manual; Digilent的PmodIAâ ?? ¢阻抗分析仪参考手册


型号：	PMODIA_RM
厂家：	ETC
描述：	Digilent PmodIAâ¢ Impedance Analyzer Reference Manual Digilent的PmodIAâ ?? ¢阻抗分析仪参考手册
文件：	总3页 (文件大小：200K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

Digilent PmodIA™ Impedance

Analyzer Reference Manual

1300 Henley Court | Pullman, WA 99163

(509) 334 6306 Voice and Fax

Revision: November 01, 2012

Note: This document applies to REV A of the board

Overview

The PmodIA is an impedance analyzer built

around the Analog Devices AD5933

Impedance Converter Network Analyzer.

Features include:

•

I²C communication interface

capable of measuring impedances

ranging from 100Ω to 10 MΩ.

programmable frequency sweep: start

frequency, step increment, and number

of steps.

•

clock (SCL) respectively on the PmodIA. (See

Table 1.) The following instructions explain

how to read and write to the device.

•

programmable gain amplifier

external clock generation optional

You must consider two protocols when writing

to the PmodIA: the write byte/command byte

and the block write. Writing a single byte from

the master to the slave requires the master to

initiate a start condition and send the 7-bit

slave address. You must hold the read/write bit

low to write to the slave device successfully.

The PmodIA should set the slave address as

0001101 (0x0D) upon startup. After the slave

acknowledges it’s address, the master must

send the address of the register it wants to

write to. Once the slave acknowledges receipt

of this address, the master will send a single

data byte that the slave should acknowledge

with a return bit. The master should then issue

a stop condition.

Functional Description

The PmodIA uses an 8-pin connector that

allows for I²C communication. There is also a

1-pin connector that allows you to select either

a high or low impedance measurement.

The PmodIA measures impedance by emitting

an AC voltage at a known frequency and

sampling the frequency response to identify

the unknown impedance value. You can

access the voltage output via the SMA

connector J3. SMA connector J4 captures the

response.

Please see the AD5933 data sheet, available

from www.analog.com, for more detailed

information on controlling the analyzer.

You can also use this protocol to set a pointer

for a register address. After the master sends

the slave address and write bit, and the slave

responds with an acknowledge bit, the master

sends a pointer command byte (10110000, or,

0xB0). The slave will assert an acknowledge

bit and then the master will send the address

of the register to point to in memory. The next

time the device reads from or writes data to a

I²C Interface

The PmodIA acts as a slave device using I²C

communication protocol. The I²C interface

standard uses two signal lines. These are I²C

data and I²C clock. These signals map to the

serial data (SDA) and serial

Doc: 502-246

page 1 of 3

PmodIA Reference Manual

Note: The pointer must be set prior to using

block write or block read protocols.

number of steps in the sweep, and the

frequency increment after each step. The

starting frequency and the increment per step

parameters are stored as 24-bit words. The

number of steps parameter is stored as a 9-bit

word.

You can perform a block write protocol in a

similar fashion to setting a pointer. Send the

block write command (10100000, or, 0xA0) in

place of the pointer command, and the number

of bytes being sent (represented as a byte) will

take the place of the register address with

subsequent data bytes being zero indexed.

Use the same two protocols when reading data

from the PmodIA: receive byte and block read.

You can program the peak-to-peak voltage of

the output frequency in the sweep by setting

bits 10 and 9 in the control register.

Once the circuit has been excited, it takes

some time to reach its steady state. You can

program a settling time for each point in the

frequency sweep by writing a value to register

addresses 0x8A and 0x8B. This value

represents the number of output frequency

periods that the analog-to-digital converter will

ignore before it starts sampling the frequency

response. (See Table 2 for a list of registers

and their corresponding parameters.)

Connector J1 – I²C Communications

Pin Signal Description

1, 2 SCL

3, 4 SDA

5, 6 GND

7, 8 VCC

I²C clock

I²C data

Power supply Ground

Power supply (3.3V/5V)

Table 1. Interface Connector Signal Description

Frequency Sweep Parameter Storage Registers

Clock Source

Control register (Bit-10

and Bit-9 set peak-to-

peak voltage for the

output frequency).

Start frequency (Hz)

The PmodIA has an internal oscillator that

generates a 16.776MHz clock to run the

device. You can use an external clock by

loading IC4 on the PmodIA and setting bit 3 in

the control register (register address 0x80 and

0x81).

0x80, 0x81

0x82, 0x83, 0x84

0x85, 0x86, 0x87

0x88, 0x89

Increment per step (Hz)

Number of steps in sweep

Settling time (Number of

output frequency periods)

The PmodIA schematic provides a list of

recommended oscillators. The schematic is

available from the PmodIA product page at

www.digilentinc.com.

0x8A, 0x8B

You can calculate the 24-bit word to store at

the register addresses for the start frequency

and the increment per step parameters using

the start frequency code and frequency

increment code equations below. You can

also find these equations and more information

in the AD5933 data sheet.

Setting up a Frequency Sweep

The electrical impedance, ꢀ, of a circuit can

vary over a range of frequencies. The PmodIA

allows you to easily set up a frequency sweep

to find the impedance characteristics of a

circuit.

ꢁꢂꢃꢄꢂꢅꢆꢄꢇꢈꢉꢇꢊꢋꢌꢅꢍꢎꢏꢇ:

ꢑꢒꢓꢔꢕꢖꢒꢗꢅꢘꢔꢙꢚꢔꢙꢅꢛꢙꢜꢖꢙꢅꢝꢖꢒꢓꢔꢒꢞꢟꢠ

First, you must set up an I²C interface between

the host board and the PmodIA. The PmodIA

requires three pieces of information to perform

a frequency sweep: a starting frequency, the

= ꢐ

ꢧ ∗ 2^ꢨꢩ

ꢢꢣꢤꢥ

ꢡ

ꢦ

www.digilentinc.com

page 2 of 3

PmodIA Reference Manual

ꢲ ꢲ

ꢆꢄꢇꢈꢉꢇꢊꢋꢌꢅꢪꢊꢋꢄꢇꢫꢇꢊꢂꢅꢍꢎꢏꢇ:

ꢑꢒꢓꢔꢕꢖꢒꢗꢅꢝꢖꢒꢓꢔꢒꢞꢟꢠꢅꢬꢞꢟꢖꢒꢭꢒꢞꢙ

Where Z is the magnitude and ∠θ is the

phase angle:

= ꢐ

ꢧ ∗ 2^ꢨꢩ

ꢢꢣꢤꢥ

ꢨ

ꢡ

ꢦ

ꢲ ꢲ

ꢴ

ꢀ =ꢅ ꢑꢒꢜꢮ + ꢬꢭꢜꢰꢕꢞꢜꢖꢠ

ꢬꢭꢜꢰꢕꢞꢜꢖꢠ

∠ꢳ =ꢅꢙꢜꢞ^ꢵꢶ

ꢑꢒꢜꢮ

Once you have set these parameters, perform

the following steps to start the frequency

sweep (paraphrased from the AD5933 data

sheet):

The PmodIA does not perform any

calculations. After each DFT, the master

device must read the values in the Real and

Imaginary registers.

1) Enter standby mode by sending the

standby command to the control

2) Enter the initialize mode by sending an

initialize with start frequency command

to the control register. This allows the

circuit being measured to reach its

steady state.

In order to calculate the true impedance you

must take into account the gain. You can find

an example gain factor calculation in the

AD9533 data sheet.

Temperature Readings

3) Start the frequency sweep by sending

the start frequency sweep command to

the control register.

The PmodIA has a self-contained, 13-bit

temperature sensor to monitor device

temperature. Please refer to the AD5933 data

sheet for more information on controlling this

module.

Impedance Calculations

The analog-to-digital converter samples the

frequency response from unknown

impedances at up to 1MSPS with 12-bit

resolution for every point in the frequency

sweep. Before storing the measurements, the

PmodIA performs a Discrete Fourier Transform

(DFT) on the sampled data (1,024 samples for

each frequency step). Two registers store the

DFT result: the Real Register, and the

Imaginary Register.

The AD5933 data sheet has a complete table

of register addresses.

Electrical impedance contains both real and

imaginary numbers. In Cartesian form, you can

express impedance with the equation:

ꢀ = ꢅꢑꢒꢜꢮ + ꢯ ∗ ꢬꢭꢜꢰꢕꢞꢜꢖꢠ

Where Real is the real component, Imaginary is

the imaginary component, and ꢯ is an

imaginary number (equivalent to ꢕ =ꢅ −1, in

ꢱ

mathematics). You can also represent

impedance in polar form:

ꢲ ꢲ

ꢬꢭꢚꢒꢗꢜꢞꢟꢒ =ꢅ ꢀ ∠ꢳ

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page 3 of 3

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