delabs Circuits

Tuesday, March 17, 2015

Digital Programmable Gain Amplifier

I read your post which is about, Digital gain control of Op-amp.  I have some questions to ask, if possible.  Please reply ASAP.

Precision Amplifier with Digital Control  (only for DC and low audio frequency)

Mail from KAM of UAE

Reply by delabs - Ask, i will try to reply.

I am student and I have a lab project to work on. It is about a digitally controlled variable gain amplifier. So, is your post relates to my topic. If you know a simple way of design, help me please. I will appreciate it.

KAM

See these links and tell me if this is what you are looking for. These are for Communications.

LMH6517 Digital Controlled Variable Gain Amplifier Evaluation Board

LMH6517 Digital Controlled Variable Gain Amplifier Evaluation Board

The LMH6517EVAL evaluation board is designed to aid in the characterization of TI`s High Speed LMH6517 Digital Controlled Variable Gain Amplifier

MAX2027 IF Digitally Controlled Variable-Gain Amplifier

The MAX2027 high-performance, digitally controlled variable-gain amplifier is designed for use from 50MHz to 400MHz.

The circuit i have on my site  is for low frequency and DC. used in instruments.  What you may need is for RF.  What is the Application DC, AC, or RF ?

Reply by delabs

My input is an AC signal, and I want to have changeable gains, I mean that one time the gain should  be 50,  100, 150, and 200.  However, this changeable gain should be controlled by digital inputs.  So, I think this is what the circuit do.

KAM

Gain of 200 means you may need more than one stage of amplification.The circuit of mine can be used for DC and Lower Audio Frequencies.  

If you go above 2K Hz the Slew Rate and The bandwidth of the Amp IC must be chosen carefully. These are the areas you have to study and choose. Then this circuit with fast opamps can cover Audio Frequency. 

At each stage you must study the Bandwidth response and plot a curve and use compensating caps if required. In case you want a uniform gain over a wide range over a wide range 

TDA9901 Digital programmable gain amplifier

If this is for a Very Wide bandwidth measuring instrument, it is very difficult. You may have to use special low capacitance switching elements. I can only give you ideas and links, i cannot design a circuit for you. You have to figure that out, that is how you learn. Use the internet more and study the circuits and concepts and ask me the doubts you have.

Reply by delabs

I really do not want you to design it for me. I want to learn.  The good news is that is i manage to design everything, but, I got confused when it comes to control the variable gain amplifier digitally.  I tried to use decoder and multiplexer, but, it does not work.  Can you give me some advice.  Sorry for annoying you, and thank you for your gentle help.

KAM

See this

LTC6910 - Digitally Controlled Programmable Gain Amplifiers

The LTC6910 family are low noise digitally programmable gain amplifiers (PGAs) that are easy to use and occupy very little PC board space.


Low Noise AC Amplifier with Programmable Gain and Bandwidth

Two LTC6910 programmable gain amplifiers can be combined to provide independent gain and bandwidth control using two 3 bit digital words. The Gain Control PGA simply varies the circuit gain from 1 to 100. T