Transimpedance amplifier
Keywords
electrical, unidirectional
Ports
| Name | Type |
|---|---|
| input | Electrical Signal |
| output | Electrical Signal |
Properties
General Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
name Defines the name of the element. |
Transimpedance Amplifier | - | - |
|
annotate Defines whether or not to display annotations on the schematic editor. |
true | - | [true, false] |
|
enabled Defines whether or not the element is enabled. |
true | - | [true, false] |
|
type Defines the element unique type (read only). |
Transimpedance Amplifier | - | - |
|
description A brief description of the elements functionality. |
Transimpedance amplifier | - | - |
|
prefix Defines the element name prefix. |
TIA | - | - |
|
model Defines the element model name. |
- | - | - |
|
library Defines the element location or source in the library (custom or design kit). |
- | - | - |
|
local path Defines the local path or working folder $LOCAL for the element. |
- | - | - |
|
url An optional URL address pointing to the element online help. |
- | - | - |
Standard Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
differential output Defines whether or not to the amplifier has differential output ports. |
false | - | [true, false] |
|
transimpedance Defines the transimpedance of the amplifier. |
5 |
kOhms* *std. unit is Ohms |
[0, +∞) |
|
normalized transimpedance gain Defines whether or not to use measured s-parameters or to use an analytical filter for the frequency dependent normalized gain. |
analytical | - | [analytical, measured |
|
cutoff frequency The 3-dB cutoff frequency of the equivalent filter (full with at half maximum, FWHM). |
0.75 * %bitrate% | Hz | (0, +∞) |
|
order Defines the equivalent filter order. |
4 | - | [1, 10] |
|
s parameters A matrix editor for users to read the element current s-parameters. |
<9> [0, 0, 0,...] | - | - |
|
load from file Defines whether or not to load s-parameters from an input file or to use the currently stored s-parameters. |
false | - | [true, false] |
|
s parameters filename The file containing the s-parameters. Refer to the Implementation Details section for the format expected. |
- | - | - |
|
equivalent input noise Defines the total input RMS noise. |
1 |
uA* *std. unit is A |
[0, +∞) |
|
equivalent noise bandwidth Defines the total input RMS noise. |
0.75 * %bitrate% | Hz | (0, +∞) |
Numerical Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
enable noise Defines whether or not to enable noise. |
true | - | [true, false] |
|
automatic seed Defines whether or not to automatically create an unique seed value for each instance of this element. The seed will be the same for each simulation run. |
true | - | [true, false] |
|
seed The value of the seed for the random number generator. A value zero recreates an unique seed for each simulation run. |
1 | - | [0, +∞) |
|
s parameters convention Defines whether the s-parameters use 'physics' or 'engineering' convention.To convert from 'engineering' to the default 'physics' convention, the element uses the complex conjugate of the s-parameters instead. |
engineering | - | [physics, engineering |
Numerical/Digital Filter Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
single tap filter Defines whether or not to use a single tap digital filter to represent the element transfer function in time domain. |
false | - | [true, false] |
|
number of taps estimation Defines the method used to estimate the number of taps of the digital filter. |
fit tolerance | - | [disabled, fit tolerance, group delay |
|
filter fit tolerance Defines the mean square error for the fitting function. |
0.001 | - | (0, 1) |
|
window function Defines the window type for the digital filter. |
rectangular | - | [rectangular, hamming, hanning |
|
number of fir taps Defines the number of coefficients for digital filter. |
256 | - | [1, +∞) |
|
maximum number of fir taps Defines the number of coefficients for digital filter. |
4096 | - | [1, +∞) |
|
filter delay Defines the time delay equivalent to a number of coefficients for digital filter. |
0 | s | [0, +∞) |
|
initialize filter taps Defines whether to use the initial input signal to initialize filter state values or to set them to zero values. |
false | - | [true, false] |
Diagnostic Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
run diagnostic Enables the frequency response of the designed filter implementation and the ideal frequency response to be generated as results. |
false | - | [true, false] |
|
diagnostic size The number of frequency points used when calculating the filter frequency response. |
1024 | - | [2, +∞) |
Results
| Name | Description |
|---|---|
| diagnostic/response #/transmission | The complex transmission vs. frequency corresponding to the ideal and designed filter. |
| diagnostic/response #/gain | The gain vs. frequency corresponding to the ideal and designed filter. |
| diagnostic/response #/error | Mean square error comparing the frequency response of the designed filter implementation with the ideal frequency response. |
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Implementation Details
The transimpedance amplifier (TIA) is often implemented using operational amplifiers with inverting configuration. It is a current to voltage converter and has two premises:
1. The current to the two input nodes (node 1 and 2) is zero;
2. The voltage difference between the two input nodes (node 1 and 2) is zero.
The following figure is a simplified transimpedance amplifier with a single output port in reference to the ground:
The DC gain is defined as
|
$$ - I_{p} = \frac{V_{out}}{R_{f}} $$ |
(1) |
The capacitance across the input terminals of the transimpedance amplifier introduces low-pass filter in the feedback path. One common type of transimpedance amplifier is in the form of an inverting integrator (also known as the Miller integrator) as shown below:
And the closed-loop gain is calculated as:
|
$$ \frac{V_{out}}{V_{in}} = - \frac{1}{\frac{R}{R_{f}}+s C R} $$ |
(2) |
The gain is the transfer function of a low-pass single-time-constant circuit. The low-pass filter in the model is defined by the parameters "cutoff frequency" and "order".
A differential output TIA has two output ports with the output voltages varying about the same DC center (typically 0 V) in opposite amplitudes.
The model allows user to load in a normalized transimpedance gain (normalized transfer function) file in TouchStone format. Theoretically, the normalized transimpedance gain defined in the file should be smaller than 1 and the gain spectrum defined in the file will re-shape the gain curve of the TIA.
The following figure shows the circuit in the example file transimpedance_amplifier.icp. The current output from the PIN photodiode is amplified by the TIA with a transimpedance gain of 5 kΩ. The TIA has an equivalent 4th order low-pass Bessel filter effect with a 18.75 GHz cutoff frequency.
The current output from the photodetector and the voltage output from the TIA are shown below:
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