A simple delta sigma converter using XSPICE
according to 
Schreier, Temes: Understanding Delta-Sigma Data Converters, 2005
Fig. 2.13, p. 31; Fig. 2.27, p.58


delta-sigma-1.cir
converter complete, tested against sine input

mod1-ct.cir
first order modulator
consists of analog continuous time integrator and
digitally latched comparator

count-latch-dac.cir
contains subcircuits of 
10 bit digital latch
10 bit counter, non-revolving, saturating
simple 10 bit DAC with analog B source

mod1-ct-test.cir
test of modulator with sine input, shows noise shaping 20dB/decade

counter-test.cir
simple test with reset
