Analog lockbox v2

Overview

This repository contains the design files for the analog lockboxes used in the B219 Cs cavity atom interferometer experiment. Like most of our PCBs, it is designed to be powered via JST connector from a dedicated regulated DC power supply board. The board, with mostly edge facing SMAs and POTs, has a narrow profile for space-efficient mounting in a 3U 19" subrack. Our front panels have outer holes to mount within a 3U subrack and inner holes for both the 12HP Vector Electronics EMB subrack modules and the 104x55 mm Hammond 1457 series enclosures.

Circuit

The circuit design, pictured below, is based on the so-called "Holger's World Famous Lockbox" commonly used in the Müller group. It is essentially just an analog PI loop with the addition of a Schmitt trigger looped in with the integrator in order to internally produce a triangle wave. N.B. The schematic shows very high resistor and potentiometer values. Do not use these high values if you want MHz bandwidth. Use only 1kR-10kR in the fast loop. One can add an optional external error bias (via SMA) and/or manual error bias (via trimpot) enabled by jumpers. The output bias for the fast and slow locks are also enabled by jumpers; usually just one output bias is needed, unless, e.g., you want to bias a piezo to a certain voltage using the slow lock. The internal triangle wave ramp has a variable amplitude and frequency whic is set by two trimpots RV5 (changes amplitude and frequency) and RV6 (changes frequency). Note that the I gain also affects the frequency of the ramp. Both the fast and slow outputs have optional shunt diodes for setting voltage limits. Most of the op amp rails have dual bypass caps--a ceramic cap at 100 nF, and a electrolytic cap at 10 μF (more lossy than ceramic to damp parasitic LC resonances between the caps)--though it is not neccessary to place the larger electrolytic caps at every op amp.

Board

PCB

Front Panel

If using an anodized/powder coated front panel (which looks a lot sexier than plain aluminum), one should countersink the mounting holes to ensure grounding to the main chassis.

Back Panel

The back panel is left unanodized for better grounding (since aesthetics don't matter as much).

BoM

Instructions for Assembly