The network divides Vin → Vfb with a frequency-dependent ratio. Three regimes (as in the hand sketch):
Low f — all caps open: Vfb/Vin = R3/(R1+R2+R3) (lowest gain).
Mid f — Cz shorts R2 → gain rises to R3/(R1+R3) (the zero, then a pole levels it into a plateau).
High f — Cp shorts R3 → gain rolls off toward 0 (the HF pole).
This gives a band-pass-like boost: exactly the shape in your sketch — flat low, a bump/plateau in the middle, roll-off at high frequency. In DC-DC feedback this is a feed-forward zero (Cz) used to add phase lead near crossover, with Cp filtering switching noise.
2 · Transfer function & corner frequencies
With Z2 = R2‖Cz = R2/(1+sR2Cz) and bottom leg Zb = R3‖Cp = R3/(1+sR3Cp), the exact transfer function is H(s) = Zb/(R1+Z2+Zb):
One zero and two poles (matching the sketch's 3 corners). Symbolically verified. The standard first-order corner labels:
#
Singularity
Sketch label
Exact expression
Note
1
Zero (boost starts)
R2·Cz
f_z = 1/(2π·R2·Cz)
✅ exact
2
Pole (levels the boost)
R3·Cz
≈ 1/(2π · Cz·R2(R1+R3)/(R1+R2+R3))
approx.; R3·Cz only in special case
3
Pole (HF roll-off)
(R1+R3)·Cp
f_p = 1/(2π·(R1‖R3)·Cp)
⚠️ exact uses R1‖R3, not R1+R3
🔎 Finding: the HF pole sits at R1‖R3 = R1·R3/(R1+R3), matching TI's feed-forward pole 1/(2π·(R1‖R2)·Cff) (SLVA289B). The sketch's (R1+R3) is a labeling approximation. The tool below always solves the exact quadratic, so plots are correct regardless.
3 · Interactive component values
Ω
Ω
Ω
pF
pF
R in ohms, C in picofarads. Everything recomputes live.
4 · Poles / zeros & resistance split
DC gain –
Plateau gain (R2 shorted) –
Peak boost –
Vout est. @ Vref=0.8 V –
Rank
Type
Frequency
Relative position
Bars are log-scaled across the plotted band (10 Hz – 10 MHz).
5 · Bode plots
Magnitude |H| (dB)
Phase ∠H (degrees)
6 · 🔗 One-click shareable preload link
This link encodes the current values in the URL. Opening it reproduces this exact analysis (all fields prefilled):
Format: …/index.html?R1=10000&R2=100000&R3=10000&Cz=1000&Cp=1000 — R in Ω, C in pF.