[sdiy] IC design books as a source of discrete OTA schematics?

[Magnus Danielson]

Hi Justin,

On 09/17/2012 02:48 PM, Justin Owen wrote:
> Hi Magnus,
>
>> A good warm-up is for instance this article:
> http://www.idea2ic.com/LM13600/UsingOTAs2.pdf
>
>> It can be a good exercise to get and read datasheets for the classics,
> and see how their topology changes over time.
>
> That, a couple of other articles and the 'simplified schematic' pages of a few select OTA data sheets has been my entire OTA library for the last year or so - which is why I wanted to take a step up.
>
>> Essentially, you have a diff-pair and 4 current mirrors.
>
> This was one of the specific questions I had - why/how does increasing the number of current mirrors improve the performance? You can make an OTA with a single current mirror on top of the diff-pair but I've seen versions with 2 and versions with 4 current mirrors (plus the output stages). The type of current mirror can change as well - most of the time it's a 2x transistor mirror - but I've seen versions using a 4x transistor mirror.

Consider the current mirrors as buffer amps. They assist to separate 
voltages from currents. This will isolate the voltage of the diff-pair 
from the output and ensures that the output has high impedance (a good 
thing for a current source) as well as keeping the input voltage to 
output voltage low. All good things you want.

>> You can then
> learn more on current mirrors and how good various variants performs.
> Current mirrors is a design which re-occurs over and over again in IC
> design, so it's well covered in the Gray&  Meyer book. It also covers
> linearization and Gilbert cells.
>
> That sounds like what I'm after. alibris.co.uk had a copy for a fiver which I grabbed along with the Delton Horn book Dan suggested - thanks to you both.

Great.

Cheers,
Magnus