| name | amp-copilot |
| description | Amplifier design copilot — topology selection, sizing via gm/Id lookup tables, PVT corner validation, and process-portable design. Use when designing amplifiers (OTA, opamp, comparator), selecting topology from specs, sizing transistors, or characterizing a new process node. Also triggers on keywords like amplifier, OTA, opamp, gain-bandwidth, CMRR, PSRR, slew rate. |
| argument-hint | ["circuit type and specs","e.g. \"two-stage OTA GBW=50MHz CL=10pF\""] |
| allowed-tools | Bash(virtuoso *) Read Write |
Amplifier Copilot
Systematic amplifier design flow: specs → topology → gm/Id sizing → simulation → PVT validation.
Inspired by Amplifier-Copilot (25 topologies, 7400+ pre-characterized designs, 4 process nodes).
Design Flow Overview
┌─────────────────────────────────────────────┐
│ 1. SPEC CAPTURE │
│ Gain, GBW, CL, VDD, PM, CMRR, ... │
├─────────────────────────────────────────────┤
│ 2. TOPOLOGY SELECTION │
│ Match specs → best topology │
├─────────────────────────────────────────────┤
│ 3. PROCESS CHARACTERIZATION (gm/Id) │
│ Sweep VGS × L → lookup tables │
│ Store in process_data/<pdk>/ │
├─────────────────────────────────────────────┤
│ 4. TRANSISTOR SIZING │
│ Role-based gm/Id → W/L per device │
├─────────────────────────────────────────────┤
│ 5. SIMULATION & VERIFICATION │
│ DC → AC → tran → PVT corners │
└─────────────────────────────────────────────┘
1. Spec Capture
Gather design requirements in structured format:
{
"name": "bandgap_ota",
"topology": null,
"process": "smic13mmrf",
"vdd": 1.2,
"specs": {
"gain_db": {"min": 60, "target": 70},
"gbw_mhz": {"min": 5, "target": 10},
"phase_margin_deg": {"min": 60},
"cl_pf": 5,
"cmrr_db": {"min": 60},
"psrr_db": {"min": 50},
"slew_rate_Vus": {"min": 5},
"power_uw": {"max": 200},
"input_range": "rail-to-rail",
"output_range": {"min_headroom_mv": 200}
}
}
2. Topology Selection
25 Amplifier Topologies (from Amplifier-Copilot database)
Single-stage:
| Topology | Gain | Speed | Area | Use case |
|---|
| Telescopic | 40-60dB | High | Small | High-speed, limited swing |
| Folded-Cascode | 50-70dB | Med-High | Med | General purpose |
| Recycling FC | 60-80dB | High | Med | Enhanced speed |
| Current-Mirror | 40-50dB | Med | Small | Simple loads |
Two-stage:
| Topology | Gain | Speed | Area | Use case |
|---|
| Miller OTA | 60-80dB | Med | Med | General purpose |
| Ahuja Comp | 70-90dB | Med-High | Med | Better PSRR |
| Indirect Comp | 70-90dB | High | Med | High speed two-stage |
Multi-stage / Special:
| Topology | Gain | Speed | Area | Use case |
|---|
| 3-stage NMC | 80-120dB | Low | Large | Ultra-high gain |
| Rail-to-Rail | 50-70dB | Med | Large | Full swing I/O |
| Class-AB | 50-70dB | Med | Med | High drive |
| Comparator | - | Very High | Small | Decision circuit |
Selection Logic
IF gain > 80dB → multi-stage (Miller, NMC)
IF gain 50-80dB AND gbw > 100MHz → recycling FC / indirect comp
IF gain 50-80dB AND gbw < 100MHz → folded-cascode / Miller
IF gain < 50dB → telescopic / current-mirror
IF input_range == "rail-to-rail" → rail-to-rail topology
IF output swing > VDD-400mV → class-AB output
IF power < 10µW → subthreshold (gm/Id > 20)
3. Process Characterization (gm/Id Lookup Tables)
Process Data Directory Structure
Store per-process characterization data for reuse across designs:
process_data/
├── smic13mmrf/
│ ├── config.json # Process metadata
│ ├── nmos_lookup.json # NMOS gm/Id tables
│ ├── pmos_lookup.json # PMOS gm/Id tables
│ └── corners.json # PVT corner definitions
├── tsmc22ull/
│ ├── config.json
│ ├── nmos_lookup.json
│ ├── pmos_lookup.json
│ └── corners.json
└── tsmc65/
└── ...
Process Config (config.json)
{
"name": "smic13mmrf",
"node": "130nm",
"vdd_options": [1.2, 3.3],
"nmos_device": "n12",
"pmos_device": "p12",
"l_min": 120e-9,
"l_values": [200e-9, 300e-9, 500e-9, 1e-6, 2e-6],
"w_default": 1e-6,
"vgs_range": [0.2, 1.2],
"vgs_step": 0.05,
"model_file": "/foundry/smic/013mmrf/.../ms013_io33_v2p6_7p_spe.lib",
"model_sections": ["tt", "res_tt", "dio_tt", "bjt_tt", "mim_tt"],
"testbench": {
"lib": "FT0001A_SH",
"nmos_cell": "gmid",
"pmos_cell": "gmid_pmos",
"nmos_inst": "/NM0",
"pmos_inst": "/PM0"
}
}
Lookup Table Format (nmos_lookup.json)
{
"process": "smic13mmrf",
"device": "n12",
"w": 1e-6,
"data": [
{
"l": 500e-9,
"points": [
{"vgs":0.35, "gmid":20.68, "gain":184.4, "id":0.88e-6, "idw":0.88, "vov":-0.008, "ft":1.037e9, "vth":0.358, "gds":4.77e-9, "cgs":5.4e-14},
{"vgs":0.40, "gmid":17.38, "gain":179.5, "id":2.29e-6, "idw":2.29, "vov":0.042, "ft":1.793e9, "vth":0.358, "gds":12.8e-9, "cgs":6.2e-14},
{"vgs":0.45, "gmid":13.93, "gain":163.3, "id":5.01e-6, "idw":5.01, "vov":0.092, "ft":2.752e9, "vth":0.358, "gds":42.7e-9, "cgs":8.1e-14},
{"vgs":0.50, "gmid":11.00, "gain":140.1, "id":9.31e-6, "idw":9.31, "vov":0.142, "ft":3.765e9, "vth":0.358, "gds":66.4e-9, "cgs":12e-14},
{"vgs":0.60, "gmid":7.19, "gain":95.0, "id":22.64e-6, "idw":22.64,"vov":0.242, "ft":5.633e9, "vth":0.358, "gds":171e-9, "cgs":18e-14}
]
},
{
"l": 200e-9,
"points": [...]
}
]
}
Characterization Script (via virtuoso-cli)
To characterize a new process, run this automated flow:
virtuoso sim setup --lib <LIB> --cell <GMID_TB> --view schematic
virtuoso skill exec 'resultsDir("/tmp/process_char")'
virtuoso skill exec 'modelFile(list("<model_path>" "tt") ...)'
for L in 200e-9 300e-9 500e-9 1e-6 2e-6; do
for VGS in $(seq 0.20 0.05 1.20); do
virtuoso skill exec "desVar(\"L\" $L)"
virtuoso skill exec "desVar(\"VGS\" $VGS)"
virtuoso skill exec 'run()' --timeout 60
virtuoso sim measure --analysis dcOp \
--expr 'value(getData("/NM0:gm" ?result "dcOpInfo"))' \
--expr 'value(getData("/NM0:ids" ?result "dcOpInfo"))' \
--expr 'value(getData("/NM0:gds" ?result "dcOpInfo"))' \
--expr 'value(getData("/NM0:vth" ?result "dcOpInfo"))' \
--expr 'value(getData("/NM0:cgs" ?result "dcOpInfo"))' \
--format json
done
done
4. Transistor Sizing
Role-Based gm/Id Selection
Each transistor in the amplifier has a role that determines its optimal gm/Id:
def size_transistor(role, spec, lookup_table):
# Select gm/Id based on role
gmid_target = {
"input_pair": 12-15, # balance noise, gain, speed
"cascode": 8-12, # moderate Vov for headroom
"current_mirror": 5-8, # low gm → low noise contribution
"tail_source": 5-8, # matching > speed
"output_stage": 8-12, # balance swing and drive
"high_swing": 15-20, # minimize Vov for swing
"high_speed": 4-6, # maximize fT
}[role]
# Calculate Id from gm requirement
Id = gm_required / gmid_target
# Lookup Id/W from table at chosen L
IdW = interpolate(lookup_table, gmid_target, L)
# Calculate W
W = Id / IdW
return W, L, Id, gmid_target
Two-Stage Miller OTA Sizing Example
Device Role gm/Id L W Id
─────────────────────────────────────────────────────
M1,M2 input_pair 14 500n 2.7µm 13.5µA
M3,M4 mirror_load 6 500n 1.0µm 13.5µA
M5 tail_source 6 1µm 2.0µm 27µA
M6 output_gm 10 300n 8.0µm 50µA
M7 output_load 6 1µm 3.0µm 50µA
Cc compensation - - 1.5pF -
Rc zero-nulling - - 2kΩ -
5. PVT Corner Validation
Standard Corner Set
{
"corners": [
{"name": "tt_25", "section": "tt", "temp": 25, "vdd_scale": 1.0},
{"name": "ss_125", "section": "ss", "temp": 125, "vdd_scale": 0.9},
{"name": "ff_m40", "section": "ff", "temp": -40, "vdd_scale": 1.1},
{"name": "sf_25", "section": "sf", "temp": 25, "vdd_scale": 1.0},
{"name": "fs_25", "section": "fs", "temp": 25, "vdd_scale": 1.0}
]
}
Validation Metrics (13 performance parameters)
virtuoso sim measure --analysis ac \
--expr 'dB20(value(VF("/OUT") 1))'
--expr 'cross(dB20(VF("/OUT")) 0 1 "falling")'
--expr 'value(phase(VF("/OUT")) <ugb>)+180'
virtuoso sim measure --analysis tran \
--expr 'slewRate(VT("/OUT") 10 90 "rising")'
--expr 'slewRate(VT("/OUT") 90 10 "falling")'
--expr 'settlingTime(VT("/OUT") <final> 0.1)'
Pass/Fail Report
tt_25 ss_125 ff_m40 sf_25 fs_25 SPEC
Gain (dB) 72.1 68.3 74.8 70.2 71.5 >60 ✓
GBW (MHz) 8.2 5.8 11.3 7.9 8.5 >5 ✓
PM (°) 65 71 58 63 67 >60 ⚠
SR+ (V/µs) 8.1 5.2 12.4 7.8 8.3 >5 ✓
Power (µW) 32 28 38 31 33 <50 ✓
Process Portability
Porting to a New Process
When switching to a new PDK (e.g., TSMC 22nm):
- Create testbench: Single NMOS + PMOS with VGS/L as design variables
- Run characterization:
virtuoso process char --lib myLib --cell gmid_n --inst /NM0 --type nmos --output process_data/tsmc22ull
- Save lookup tables: Auto-generated at
process_data/tsmc22ull/nmos_lookup.json
- Re-size:
virtuoso design size --gmid 14 --l 100e-9 --gm 188e-6 --pdk tsmc22ull
- Validate: Run PVT corners with new models
Quick Validation with Verilog-A Ideal Model
Before transistor-level design, validate specs with an ideal behavioral model.
Use the /veriloga skill to create an ideal opamp with target specs:
The gm/Id targets remain the same across processes — only the lookup tables (Id/W, gain, fT vs gm/Id) change. This is the core portability advantage.
Key Process-Dependent Parameters
| Parameter | Changes with process? | Impact |
|---|
| gm/Id target | No | Design intent unchanged |
| Id/W at given gm/Id | Yes | W changes |
| Self-gain at given gm/Id | Yes | May need different L |
| fT at given gm/Id | Yes | Speed limit changes |
| Vth | Yes | Bias point shifts |
| Min L | Yes | L floor changes |
Quick Reference: SKILL Oppoint Parameters
gm, gds, ids, vth, vdsat, cgs, cgd, cgg, gmbs
self_gain (= gm/gds), gmoverid (= gm/id), ft, region
Access via: getData("/INST:param" ?result "dcOpInfo")
Or: OS("/INST" "param") for waveform data
